Low compression CB750 engine teardown. Found the problem.

what's going on guys welcome back to classic octane i am taylor so in the last video you saw me get a classic cb750 running again at the end of that video i was kind of going back and forth of what to do because we discovered we had one cylinder of that engine that had low compression so my original plan was to just take one of my other cb750s get that running see if that engine was in good shape swap the engine in and be good to go but i listened to a lot of your comments and decided to do what you guys would do most people in this scenario are not gonna just have a spare cb750 laying around like i do to swap it in so we decided we're actually going to do a top end rebuild so i have the full top and rebuild kit including new piston rings um all the gaskets all the seals everything to do basically from this section all the way up so that's going to be the name of the game today this isn't going to be a how-to video on doing this process it's going to be more of an overview of me doing it and let's uh see if we can discover what's causing our low compression on the number four cylinder let's tear this thing apart before i get started i'll give you a quick rundown of all the parts we have here so this is a complete top and gasket set i'll throw a link to all this in the description below but it has all the head gaskets valve cover gaskets exhaust i mean everything we can think of four sets of new piston rings spark plugs and then i went ahead and got one of those stainless steel allen bolt kits this uh engine actually has all stainless steel allens already the main ones i like to replace are these on the valve cover just because these you know it needs to be a nice even like solid seal across here and it's a little bit difficult to do that with these jis screws so i like to just replace them with allens and then of course the whole engine will match now that it'll be allen's all the way across so that should be everything we need i'm going to go ahead and start to pull stuff apart i'm using my second lift here as a workbench to keep all my parts nice and organized [Music] got the valve train all removed it doesn't matter how many times you've done this it's never a bad idea to just have the manual just to keep your sanity keep you know the process down of each individual step and just you know make sure you're not getting ahead of yourself also it's very important to kind of meticulously lay everything out like your rocker shafts and everything to make sure that you're not losing any bolts you're not putting any bolts in the wrong place you know all the rocker shafts and rocker arms and everything are all going back where they came out so i like to just kind of methodically lay everything out that way it's very simple for me to just kind of reverse order so i'm to the point now where i'm going to be loosening all of the head bolts or nuts i should say and it's very very important that you do this slowly and what i'm going to do is just do reverse order of what the manual calls for for tightening them and it's going to be like a crisscross kind of pattern i don't remember what it is off hand again while i have the manual out but again it's very important to not just loosen all these in one go you want to just crack them loose in reverse order and keep loosening keep loosening until they're all nice and loose and what that does is evenly releases the pressure of this head if i just started from this side and started unbolting everything the head would start to lift on this side while being stuck down and that can actually warp the head so i can't stress this part enough to just go nice and slow reverse order from what's in the manual and then we'll pull all these off we'll be ready to pull our cylinder head off [Music] all the bolts are out enough should be ready to remove work it over all the studs we need to feed our there we go there she is definitely got some build up on the valves that's for sure i want to clean that up a little bit overall it doesn't look bad looks like i'm missing a little o-ring or two but luckily we got new ones okay let's put that like here so our number four is a little bit rusty which is what i was thinking was the problem in that last video if you remember i was thinking that some water probably got into this cylinder a little bit and either caused some rust issues on the valves or you know caused some rust on our piston rings something like that i believe i had it in time lapse mode so we may have missed me pulling the cylinders off but there's no more bolts or anything it literally just pulls off right after you pull the head off so looking down in here this is our number four cylinder it's definitely got a little bit of corrosion on it it's a little bit dirty but i don't i don't feel any like heavy scoring or anything like that so i truthfully believe that that will come right back with a hone i don't think we're going to need to do any kind of machining or you know boring it out a little bit it's nothing that's that kind of damage that we'll know for sure when we hone it but it looks pretty darn good i'm going to go ahead and run the home through all of them just to get a nice cross hatch and everything back in the rest of these but one thing i did notice and so okay number one cylinder right here the piston and the piston rings you can see the piston rings are loose uh in their ring lands they're kind of being they're able to float around they're springy a little bit so they actually spring out when it's in that cylinder push against the cylinder wall and give you good ceiling aka good compression and they're nice and free on all of these pistons except for number four which is our problem cylinder you can see the rings are completely stuck in their ring lands like they're not even pushing out anywhere which is exactly what i would hope to find for a engine that had just low compression not no compression so no compression we would expect to see a hole in a piston a bent or broken valve some like heavy damage but since it was low we're like okay it's probably not catastrophic and this is exactly what we're finding here is it looks like water probably just got on the cylinder ran down the side of the piston a little bit caused these rings to get seized tight close together and we're just not getting a good enough seal truthfully if you're just a little shade tree mechanic you probably free these up slap slap this thing back together and it would probably run perfect since i'm in here i'm not going to do that i'm going to go ahead and replace these with our new rings since i have them anyway i'll probably go ahead and replace all of them just so we have fresh rings throughout the whole thing what i do want to look into now is the best way for me to start cleaning all this stuff up the pistons themselves i can pull them out and truthfully i'll probably vapor blast them some old timers are going to get really mad if i do that but vapor blasters are not very aggressive and they will not take away metal which means we should be able to blast this carbon off and leave a nice clean finish vapor blasting is used on internal engine parts all day every day no problem that being said i don't want to vapor blast the head because these are really easy for me to clean afterwards i can clean all the glass bead out blow it with compressed air you know wash them off make sure there's absolutely no remnants of glass bead or anything on the piston itself that's not going to be easy for me to do on the cylinder head just because there's way too many cracks and crevices for glass speed to get stuck in so i'm going to try and figure out a different way to clean up this combustion chamber clean all this carbon build up and everything out but i'll bring you guys back when i figure that out you can see i've cleaned one side and all i'm doing is using a little bit of solvent spraying it in here letting it sit for a little bit then i'm using some scotch brite pad you can use a bunch of different stuff for this just don't use anything that's stronger than aluminum you know you don't want to get in here with a razor blade and start scraping too crazy or some heavy duty steel brush or something like that you just don't want to be able to scratch or gouge any part of this because you can create kind of a hot spot and some issues this is a very you know finely machined surface and you just don't want to introduce any extra kind of nicks or anything so i'm going through here again it's letting it sit for a little while scrubbing it i am using a little brass brush if you're gentle with that it's fine scotch brite's working well and cleaning it all up i'm also doing the same thing on the pistons as well i was curious of how deep that carbon buildup was but really spray with solvent rub with a scotch brite and it all came right off so i don't think we're going to have to vapor blast anything so i'm going to be doing that and then i'm also going to be working on mating surfaces for head gasket cylinder base gasket all that stuff we want to make sure everything is super clean we also want to make sure that all these little o-rings and everything are accounted for so that we can replace them with the new ones when everything you know is going all back together so i'm gonna keep scrubbing we're gonna move on to this side and i'll clean up the pistons and i'll bring you guys back when i have everything clean and we're ready to put our new piston rings on making some good progress here got all my surfaces cleaned up again just with some solvent some scotch brite and everything uh came out pretty darn nice i'm uh i'm happy with that so i went ahead and pulled out one of our pistons as well this is the one that had the stuck rings in there i was able to get them out very gingerly and they broke and they were definitely corroded in there but there doesn't seem to be any damage whatsoever to the ring lands or the piston itself so i have no reason to uh think that these need to be replaced everything seems to be good cleaned up nice there's a little bit of discoloration but this is very smooth which is what you're looking for you just don't want this to be pitted or any kind of you know big gouges anything like that that's just going to become a hot spot and could potentially become a problem so what i'm doing now is i'm going to go ahead and double check the ring gap on all of our new rings i'm also i already honed these two cylinders i'll show you guys the honing process on these two here in just a minute but while i was doing this i figured i'd turn on the camera so i don't get too far ahead of myself so there's three we'll call them sets of rings the top two are just individual rings the bottom is what's called an oil control ring which has this little kind of a springy corrugated looking piece in the middle and then two thin kind of retainers on each side so that makes a little sandwich and that's what actually keeps the oil on the bottom side of the piston scrapes it off the cylinder walls then you have these two which are very very similar but if you look at the profile one of them has just slightly rounded over corners and that's going to be your top ring so consider that number one now this one happens to be kind of a two-tone color it's got like the silver on the edge where it's a little bit closer to black on the surfaces this one is a solid black this is going to be our number two ring which is almost perfectly square on the edges and then also they have little markings these have little r's on them that goes up so that just kind of keeps you know it'll be in this configuration when it's on the piston itself we'll also want to make sure that we clock these gaps so that two gaps don't match up together because that come becomes a potential spot for compression to kind of leak by so we want them about 120 degrees apart from each other whenever we go to install them but what i'm doing now is double checking that ring gap and if you're not familiar with how to do that process i'm going to kind of just gingerly put it into the cylinder here i'm going to take our piston upside down and i'm going to push it down you know maybe about a third of the way i like to use the ring lands on the piston to make sure that i have this perfectly square in the bore just like that so i'm basically just pushing it down until the cylinder surface matches all the way around that bottom ring land then what i can do is take my feeler gauge and go in here and measure that little gap and what i'm personally shooting for is about 12 000 of an inch gap the spec in the manual is only it only tells you the maximum spec it says if it's bigger than 27 thousandths of an inch replace the rings there is a lot of speculation on the internet about what they should be set to when you're going in fresh i've seen as tight as eight as high as 18 i figure i'm going to meet in the middle and i'm gonna shoot for 12 thousands which surprisingly and luckily is exactly what these are measuring out at so i'm just sticking that in there 12 000 of an inch tells me that we don't have to do any filing on this if that was super tight say there was no gap or there was two thousandths of an inch or something they have you can file these rings and you just want to make sure you kind of evenly take off very small amounts and just work your way up to whatever spec you're shooting for i'm sure someone in the comments will tell me that 12 000 is the wrong thing but we going to do it anyway so i'm going to keep going and i'm going to just spec each piston ring to each cylinder so these will become this cylinder's rings and so on and so forth just in case there's little variances in bore size we don't throw ourselves off but that's how you check piston ring gap i'm going to show you guys quickly how i hone these cylinders so i'm gonna get a little bit of lubricant and then this is the hone that i have it's just a three stone kind of spring-loaded piece you put into a drill so that you can stick this in the cylinder it will evenly press out and then you can turn the drill on run this it does not take a lot we're not trying to remove a ton of material here all we're trying to do is clean up any little spots of corrosion and then introduce what they call a cross hatch pattern which is basically fine scratches in an x pattern that just help with compression they help with those rings to have something to kind of bite onto to seal nicely i'm just going to spray a little bit in there nothing crazy stick our honey in [Music] don't go too far wipe it out we'll see how that looks not sure if you'll be able to see and it probably looks a little more aggressive than it is in person we don't want to be able to feel any of those marks or anything we just want a nice light kind of x pattern scratches for lack of a better word down the cylinders make sure there's no heavy build up anything like that and that's it so you're literally talking about maybe 10 15 seconds tops on the honing process again less is more i'd rather go back and do it three or four times instead of do it too far and end up you know kind of boring the cylinder out unintentionally knock out the last one ready to keep going got number four with the new rings in place figure i'll show you here on number one just go through it one complete time for you guys i got my number one rings here we'll pull off the old ones again keep in mind piston rings are very brittle so if you bend them too far one way or the other i'll just show you on this one if you bend it too far it'll explode into a million pieces and i probably should have worn some eye protection before doing that but luckily we are good to go so keep that in mind do not go crazy when you bend these things to get them off you just get one edge work your way around just slow and steady and make sure again you're not gouging anything you're not scratching it up and you can just pull them off they're all going to be garbage these little oil control ones can be kind of a pain but you just find the area where it's the gap is and you can generally get a little nail in there and separate it out [Music] like that we'll find the gap on this corrugated piece which is right here and it's out you can pull the pistons out to do this if you want i'm just going to do it with them in the are on the connecting rod still just so that it kind of helps support it so when we're going back on we're going to do the oil control ring first slide it around get it in that very bottom slot and then we have our two little center rings that go on the top and bottom of that boom that one is in so kind of spin it around make sure everything's moving nice and free everything's where it should be and we can move on to the next one you remember from just a second ago it's the one with the perfectly square edges in this particular case it's the one that's one solid color we want to make sure our little mark is facing up work it around not bending it too much number two rings in place we're gonna set that gap right over here about the four o'clock position or so and we'll go for our top ring we're going to want to set that gap about 120 degrees off so i'm gonna shoot that for somewhere around this seven o'clock area seven eight o'clock something like that just you know a decent amount of distance you don't want the gaps right in the front or right in the back of the piston either not entirely sure why that is but the manual does say that and there we are so all of our rings are in place the gaps are staggered we're ready to move on rinse and repeat [Music] um now that all the piston rings are in place we are ready for reassembly i don't think i mentioned it earlier but uh my cam chain tensioner is in good condition this would be a good time to replace those wheels if they are heavily worn out or you know have any kind of issues they're like 15 dollars it's not a bad idea to do them uh mine like i said is in good condition i honestly think that this engine was a part not all of that long ago because almost every single gasket surface the gasket just came right off if it's like an original you know 40 plus year old engine that's never been opened before i have to do so much scraping and so much more cleaning to get the gaskets off this one the gaskets came off so i'm thinking probably i don't know last decade 15 years maybe this engine's probably been apart before so here's all of the o-rings and gaskets and everything that come in your top-end gasket kit they're all pretty self-explanatory um i'll just kind of go through really quick these are our four really thin o-rings those actually go on the bottom of the cylinders right around here you can actually see the old o-rings in those little grooves so that's where those four o-rings go next we'll just move on to these these are for our tappet covers so they replace the o-rings in here exhaust gaskets are the copper ones we have these kind of thicker more more like a cylinder type o-ring those go around here there's four of them right on the top of the cylinders and they meet up with a cylinder head and these four holes there four just actual o-rings that aren't you know as thick those go two of them go right here and right here you can see the little recess in there and then on the other side oh yeah on this on the block itself is where the other two go right here and right here so you can see where those two studs have kind of a little recessed area that's where those four o-rings go the four smaller o-rings go on the top side of the cylinder head and replace these little o-rings right here so there's one right there one right there there and there for oil passages these little hockey puck-looking discs are for covering up where our cylinder head uh actual nuts go through or bolts i should say so that's where those go and then of course you have your main cylinder head gasket and then bottom this greenish one that is your cylinder base gasket which goes between the block and the cylinders on this side cylinder head gasket of course goes between the cylinder and the head that's very obvious this one the thinner one is your valve cover gasket and then you have things for like the starter motor and your uh cam chain tensioner that kind of stuff so all that was probably self-explanatory but if anybody's never done this before can look a little intimidating but it's really not that many gaskets you just kind of look for where the same size is the same number of o-rings and swap it out so i'm going to go ahead and start to throw all those in i'll bring you guys back when we are placing the cylinder head back on here because it can be a little bit tricky to get all of the pistons into the cylinders at the same time making sure we don't catch and break any of our piston rings there's a bunch of different theories on the best way to do this i've done it a bunch of different ways i'm just gonna make sure that all my ring gaps are set again okay i've seen people put pieces of wood under here to support the pistons there's piston ring compressors you can put on here i find them more of a pain than that than helped on these engines if you think about like building a small block chevy or something these cylinders are built into the block so when you put the piston in you just compress it slide the piston in and then your piston ring compressor tool is just like on the top and just comes right off this the tool is kind of going to be stuck in the middle there so you got to use like a hose clamp or something anyway along with that explanation that i'm not going to use one i'm just going to kind of manually excuse me manually put them in there is a little taper on the bottom of each one of these cylinders that can kind of help you get the piston rings to slide up in there takes quite a bit of finessing and patience but it's really not too bad pull our cam chain through here make sure our tensioner and everything is in the hole and we'll just start to line these pistons up into each cylinder like so then we're just going to go cylinder by cylinder and [Music] so next up we make sure that all of our o-rings are in place we got our kind of cylinder o-rings and then our standard o-rings make sure you have your little dowels on the outside and chain tensioner all that's in the right spot we'll go through with our brand new cylinder head gasket making sure we don't bend this thing too much one direction or the other and these go on without any kind of copper spray or anything copper spray is for copper gaskets these are graphite i believe just gotta fit it over this little down like that should sit nice and flat and we are ready for our cylinder head so it's going to go on same way we just need to make sure we feed this cam chain all the way up through there surfaces clean no o-rings or anything left in place kind of hold it up while i feed this chain through the tongue here we're not pinching anything got a bunch of studs to line up just like that nice and flat seated around no issues got our cam chain through and then like here okay now we're ready for the four gis i'm going to call them uh bolts that go through these two holes these two holes and they do get those little hockey pucks as well there actually isn't any bolts through these center ones but we'll put the little blinking plugs in there as well just like this keep everything nice and sealed so we'll throw these in and they just get tightened down i don't actually know if there's a torque spec for this or not i'll have to look it up a really important torque spec is for all 16 of our head nuts that go through here and that's where we follow that sequence and we'll kind of hand tighten them all and then we'll lightly snug them all up and then we'll probably work through either one or two sequences of torque and i gotta look up what the setting is it's not a ton it's somewhere on like 15 18 foot-pounds something like that but what's most important is that we follow that pattern so that we get a nice even clamping load across the entire head [Music] little seals are in place everything's nice and torqued down so right now i want to double check that our cam will one that the engine turns over nicely too that our cam chain is still on the sprocket so yep it's moving seems moving nice and smooth it's not super easy to move so we know that seems to be having uh you know good contact with the sides of the cylinders as much as we can tell i'm also going to take this opportunity to go ahead and get the engine in the right spot to install the cam which is the t mark on the timing plate over here for the one and two cylinders so that's top dead center for one and four i mean so put it right on the t mark right there so that means number one and number four are at absolute top dead center which is where our cam needs to be installed we're ready to go for our cam retainers whatever these are officially called just slide down on their little studs you can do it ah i see our problem our old little seals are stuck on there we need those there we go now we slide around it goes much better see it just goes to show don't get ahead of yourself if something's not fitting right just take it off and double check it okay i don't know if i mentioned this when we took it apart or not but our cam bearings look to be in really good shape there's no scoring or any kind of excessive heat we'll kind of discolor them okay looking at my manual here slide these down rotate cylinder 104 in the timing mark okay now we're putting ready to put the cam back in so put it back in we need to slide it through the cam chain being careful not to neck any of the lobes here just work nice and slow go ahead and remove my welding wire hmm there okay so now let me show you on this side the little marks that you got to make sure are lined up so on the side of the can here you have this little keyway and then you have these two lines we want that keyway to be in the 12 o'clock position so straight up and then i'll have our two little lines matching with that cam retainer right there so that's exactly where we want the cam to stay and so you have to be very careful that it stays in that position and that you can get this cam sprocket installed without moving that cam too much so we'll put the cam chain on the sprocket we'll hold it up in place see i think because if i were to bolt the cam up i would have to move it just like that and that's a little bit off i think let's try to move this sprocket one one tooth boom right there so we were one tooth off and that can throw your timing way off on your bike so hopefully that all makes sense of what i just did of playing with that cam sprocket while you're installing it making sure the cam doesn't move and that you can put the chain on put the sprocket up onto the cam where we took out our two bolts earlier and that everything is nice and lined up no issues to report we're ready to throw those two 10 millimeter bolts back in here and actually bolt that sprocket to the cam for good i'm knocking out the rocker shafts now just a reverse of how they came out just slide in from the side the outside is slotted so you can use a flat blade screwdriver to orient and orientate them easy for me to say so that you can get these little bolts in there and i'll have to look and see if these have a torque spec i know the uh top of the cam bearings the cambering caps have a torque spec but i don't know if these do or not now's the time to go back on our bearing caps and these do get torqued down to what does the book say six and a half to nine and a half foot pounds so i'll run through and throw all these on tighten them up and i think the next step is probably our cam chain tensioner i'll have to see when we get there ready for the cam chain tensioner now so we just have our three bolts this thing is super simple it's basically just spring loaded so you undo the lock nut compress the spring down lock it in place for installation we're gonna put our new gasket on here go ahead and start our three bolts through just to keep our gasket aligned and just slides right in and we'll tighten our bolts down once the bolts are tightened down we can undo that lock nut and it will spring into place setting our chain tension and exactly what it needs to be moving on to valve clearance now so to get the engine in the right position basically you turn the engine clockwise until you see this number one intake valve go down and then come back up then you align your t mark with a little notch on the block now that's in the correct position for us to do intake and exhaust on number one as well as exhaust on number two and intake on number three and we're looking for two thousands on the intakes three thousands on the exhaust we're then going to turn the engine 360 degrees line that mark up again that's going to allow us to do both of them on number four as well as intake onto exhaust on three hope that makes sense it's all in the manual so i'm gonna knock out all the valve clearance and then we should be ready for our valve cover and our breather now we're ready for the valve cover i like to just hit everything in here with a little bit of oil one because this engine is going to be sitting for a couple of weeks before it's run and then two everything's really dry now and on initial startup i wouldn't mind it just being a little bit more lubricated that's good nothing crazy got a fresh gasket on there time for our cover and i do have all of my new allen bolts in here as well just like that we'll just start to kind of run these down i'll kind of run them down in a crisscross pattern it's not as critical as like bolting bolting down the head but just keeps everything from tweaking or getting kind of warped or lopsided so i'll run all these down and we're ready to throw on i'll throw on the breather anyway we'll have to take it back off uh to actually get this engine back in the frame but just so nothing falls down in here we are going to give this engine a nice clean light paint job just to kind of freshen it up and i want everything to be nice and sealed and there is a new o-ring in the kit for the breather cover as well don't forget that and the final step is our eight on our tappet covers just use a small flat blade to pull them out slide the new one on tighten them up well that's it for the 750 top end rebuild as you can see it's really not terribly complicated if you just work methodically place all your pieces out in the order that they you know come out of the engine follow the manual follow this video to somewhat like i said i didn't really want to do a how-to video but i wanted to kind of show you the important parts it's not terribly complicated i really do hope that this kind of demystifies the top-end rebuild process i know a lot of people are scared to uh to do it that's another reason that steered me towards wanting to to make this video instead of just pulling another engine testing it and putting that in the bike this is what most people would do is you know buy a hundred dollars worth of parts refresh the whole top end know all your oil seals are good your piston rings are good your head gasket's good everything's gone through adjust it properly this is a really good kind of starting point now this motor you know in theory should not have to be serviced for a long time and uh that's what i like to send my customers away with is a bike that i know is in good shape and i'm not gonna get a call a month later saying you know it's starting to puke oil out of the head gasket or something crazy so this one's all nice and taken care of it is going to be a couple of weeks before i'm putting it back in the frame just because i need to finish the rest of the modifications for the bike so it's going to be a little while before we actually hear it run but i'll make sure to take you guys along the way i appreciate you watching i'm sure this one was a long one let me know if you have any questions or anything in the comments below i'll see you guys in the next [Music] you

Channel: Classic Octane

Views: 79,555

Rating: 4.9256082 out of 5

Keywords: Honda, CB550, Cafe, Racer, Build, Project, CB750, CB350, CB360, Yamaha, Motorcycle, Garage. Shop, Update, Triumph, hardtail, bobber, chopper, welding, fab, springer, custom, trail, riding, dual, sport, pit, bike, monkey, Stunt, gloves, cam, corder, burnout, handlebar, stunts, stunting, wheelie, hd, drift, Xv1100, XvS650, Harley, Davidson, motorcycle, review, comparison, scooter, fix, tips, tricks, tools, painting, glueing, soldering, design, fabricating, solution, motovlog

Id: RKJ1ylGvZV0

Length: 43min 37sec (2617 seconds)

Published: Sat Oct 24 2020