Honda CB750 DOHC - Engine Rebuild Step by Step - Ep1

guys what is up welcome back to the letterbox workshop i'm not in the shed today in the uk we're just about to go into phase two of our lockdown which means for the next four weeks i'm not gonna be able to go to the shed unless i jog there and jog back in class it's my daily exercise which may be pushing it a little bit i haven't quite decided yet nonetheless thankfully i've got lots of editing to catch up with so i am sat here in my hotel room in copenhagen just doing some video editing in today's video we are going to be rebuilding the honda cb750 dual overhead cam engine so this one runs from about 79 onwards i believe mine's an 82 but they should all be pretty much the same so if you've got on these bikes and you'll see a bit more about how the engine works or if you're thinking about doing a rebuild yourself then stay tuned [Music] right guys let's uh start by talking about what tools you are going to need for this rebuild so this is going to be done in about five episodes this rebuild so i'll just focus on the tools that you need for the first part so we're talking about taking off the head of the bike the valves and all the way down to the pistons but not touching the bottom crankcase at all so first of all you're going to need a honda cb750 dual overhead cam engine now i say this because this video is very specific to that engine you may find that there are other displacements where the procedure is generally the same but this video is done for the cb750 uh you are going to need this on a workbench with all the oil drains now getting the engine out of this bike is not a straightforward process i have made a video on this so if you're just starting out and your bike still has the engine fitted i will link it below and at the end but you do need to get your engine on a workbench on a stable surface somehow you need a manual for the bike this video is not intended as a replacement for a workshop manual it's a supplementary material i'm just going to share some of the techniques i've learned taking this engine to pieces and rebuilding it but in the first instance i do recommend the official honda shop manual it's called that's what i've used alternative you can get the climber and haynes manuals to this bike both of which are excellent and have plenty of pictures and descriptions for how to do this rebuild if you're looking for the official honda shop manual it is available on all the usual uh honda forums that being said if you subscribe to the channel i will soon be launching my own version this document it's greatly cleaned up over the original uh it's all labeled correctly i'm going to be annotating it with advice that i've found as i've done this by being helpful so if you're interested in that subscribe to the channel and i'll be launching that in the coming months you're going to need a selection of cloths wd40 degreaser and latex gloves if your bike is anywhere near the stake mine is in this is going to help protect your hands the bikes are filthy you've got to remember this is getting on 40 years old this bike so that's just going to help you work safely and cleanly the biggest tool you're going to need is a decent metric socket set so some of you in america may be more familiar with imperial sizes on your nuts and bolts it's a japanese bike so you are going to need metric sockets i used a half inch set but a 3 8 is equally applicable for removing these but just make sure the actual sockets themselves are in millimeters you're going to need just an assortment of light hand tools screwdrivers allen keys and pliers always useful one thing you're going to specifically need is a jis screwdriver i bought one my bike called vessel about 15 or 20 bucks i think i'll link it below if you're interested but some of the screws on this bike they will look like phillips heads but they're not they are japanese industrial standards so bind your screwdriver make sure you're gonna get those out cleanly and you're not gonna risk stripping the head off them i bought a pack of these plastic shims from the local hardware store they're intended for packing out timber when you're doing carpentry work that are extremely useful when you're trying to separate engine casings for slotting into narrow gaps and supporting the engine i'll explain more as the video goes but if you have to be in the hardware shop when you see these they're normally about five bucks a pack do grab a set to be extremely useful indeed uh you're either gonna need a rubber hammer or a regular hammer and a few blocks of wood there are gonna be components on this engine that will have seized into place and will need a little tap to move them having a rubber hammer or using a piece of timber just protects the engine it's aluminium so it's very very soft so you do need to think about that in advance i bought a set of these picks on ebay i think these were a dollar or so including shipping from china i have to say the quality is actually surprisingly good and i'd probably use these more than any other tool in my workshop they're really really really useful again i'll link them below but when you're trying to get your fingers into really tight little corners you're going to need these things finally i recommend getting a set of zip lock bags and a sharpie every single nut bolt washer as it comes off the engine you want to put it straight into a bag label it and store it now putting these good practices in place from day one in your workshop will make this ten times easier to rebuild this bike don't do what loads of people do take a load of bonus off and think i'll bag it up at the end of the day then get carried away building the engine and before you know it you've got a box of parts and a nightmare on your hands so set up good practices right from the start be disciplined this doesn't sound very exciting but trust me it will make your life so much easier so that's what you're going to need let's crack on with the rebuild so first off we're going to remove the cylinder head cover this is held in place by eight cylinder head cover bolts it's always good practice with these to work in a patterns that you release the tension [Music] evenly [Music] with the eight bolts removed the head cover should lift off easily uh getting good practices place bag label the parts and you can note at this point that the four central bolts are slightly longer than the outers right in the center of the engine we have a cam chain guide and an oil line these can be removed by removing the three retaining bolts [Music] so next up we're going to remove the camshaft holders these must be removed in order bravo charlie hotel juliet i'll show you these now the letters are embossed onto the camshaft holders themselves but just be aware that bravo and charlie the letters are covered by a small town [Music] also be aware that two bolts have already been removed with the oil line so if you find he's missing don't worry [Music] so [Music] there are two small plastic oil caps these should be able to be lifted free now a single bolt in the center of the engine holds the cam chain guide retaining blade this can be removed at this point [Music] the camshaft holders are aligned for small metal dowel pin two on each holder the easiest way of removing these is a pair of needle nose pliers some of the dowels are going to remain in holders and others are going to remain with the engine just make sure you collect these all up and chuck them in the bag along with the holders [Music] if any of these dowel pins are really stuck in place the easiest way i found of getting them out was just to use a vice grip to get a strong grip on them and then to twist and hammer from the back at the same time this released the one or two that i had seized on my engine on the front of the engine there's a cam chain tensioner lock nut bolt this can be loosened right off with the lock nut loosened you should be able to push down on the lower side of the cam shape maintaining pressure on this tighten up the cam chain lock nut again and it should hold the cam chain in a loosened state with some play in it on the rear of the engine you're going to find another chain tensioner loosen this then using a vise grip work the rear cam chain loose and tighten the adjusted nut as before unfortunately my camera failed to record the video of this section we need to remove the pulsar generator cover this should be the only one on the bike with the honda logo on it behind this you'll find a large nut which will allow you to cycle the engine around you want to turn this until a small character 1.4 appears in the window at the top this tells you that cinders 1 and 4 are in the highest position if you've got this right the load should be positioned the same as in the video as long as the lobes on cylinder one are pointing at each other you're good next up we can remove the camshaft holders golf kilo foxtrot and lima in that order although i just released the tension on these gradually as before again make sure you click down pins as you go and bag these along with the camshaft with all four camshaft holders removed the intake camshaft can be lifted out through the cam tray the exhaust cam sprocket is a large cog at the front of the engine it's held in place by two small bolts these can now be removed just be aware you may have to turn the engine for 180 degrees to access the second [Music] bolt [Music] once you have both of these bolts out we're going to remove the remaining camshaft holders these need to go in the order delta tachometer gear alpha and then echo i've labeled the tachometer near gr in these diagrams and it is visibly different to the other camshaft holes [Music] [Music] [Music] at this point i decided it was a good time to remove the gasket although realistically you can remove this at any point next off we're going to remove the exhaust cam shaft now be aware when you do this the timing chain is liable to drop into the i engine case this short 12 inch length of steel or timber put in place just to prevent the dropping works perfectly it's recommended with these chains that they're reinstalled in the same orientation as they're removed from the engine i you want them to work in tension in the same direction not to reverse them now these are quite oily so it's quite difficult to actually mark up how these go around this is how the chain went in this engine what they want to avoid is it being flipped over when you reinstall it so with this particular chain i installed a set of cable ties on the top edge so i know where the cable ties are is the top of the engine and i've put a pair at the front and a single cable tie at the rear that just means in a few months time when i come to reinstalling this i know it's in the same order i'm not running the risk of any sharpie ink having run off these parts and i can 100 guarantee you'll be going in the right way so just have a think about how you're going to do it but this is how i did it on the rear of the engine you've got a short s-shaped oil line uh this could be unbolted now it's really really really easy to damage this as you undo the two bolts you can twist the actual oil line itself and kink that which will then restrict the oil flow to the head which you definitely do not want so what i did was just use a small spanner on the two nuts at the end of the oil line itself and then the bolts can be safe to remove any risk of twisting [Music] while we're on this side of the engine the two cam chain tensioner lock nuts can be removed entirely on the front of an engine you should have a small plate showing you the size of the engine there's two small bolts underneath these these can now be removed next up we're going to remove the 12 domed or acorn nuts on the top of the engine it's important you do this in a crisscross pattern similar to the sequence i'm using here and just do a quarter turn or so on each nut as you take them out now these can be fairly tight and you may find you need to use a small hammer on your spanner to release these i highly recommend you don't use a torque wrench so it's very easy to strip the bolts that go on these and that's one hell of a job to repair them so just work slowly so gently you should get there after several passes you should have most of the tension removed from these and you should just be able to remove them fully hey [Music] with these nuts removed we can now start to remove the cylinders this is where you want to use your rubber mallet or a piece of timber to protect the engine lock if you've only got a steel hammer the important thing here is to take it really slowly just get it a millimeter or two on each side once i got a small gap i inserted one of my plastic shims into it you may find that the head just wants to rock back and forth as you remove it the shims give it something to push against and but it's happening this should make it a lot easier so so you can see a lot better here how i've used these little plastic packers you'll find that when you apply pressure upwards on one end all that will happen is it will pivot through the center engine and the other end will go down so to prevent this happening and it just seesawing back and forth through the center of the engine you want to put a few plastic packers in each side as you go this means the engine's got something to bear against so that it doesn't drop when you hit the other end and you just gradually insert one or two millimeters of packers at a time just to prevent that see-sawing motion really and then you know that every small little tap of the hammer you put on into the engine it will actually move the cylinder head up a bit [Music] [Music] again as you remove the cylinder head just make sure you have a way of securing the timing chain to stop it falling down the insulation with the cylinder head removed i've decided to remove the shims and the lifters they're purely held on by the suction of the oil so i found a small metal pip was sufficient to get underneath these and remove them from the head when backing these just make sure you make a note of which position they were in so that you can make sure they go back into the same place at this point i also decided to remove the four spark plugs at this point you can also remove the front cam chain tensioner bolt there's one further bolt on the cam chain tensioner inside with these removed the cam chain tensioner [Music] [Music] at this point you're probably gonna be able to see the tops of the pistons for the first time so you can see here i've got lots of flaky bits of carbon on mine there's quite a lot of debris in here i really don't know where it's all come from but i'm certainly glad i've removed it so i give it a good clean the lower front edge of the cinders there's a single bolt which can now be removed this releases the cylinders again i've used a block of wood and some packing plastics to remove this [Music] so as you lift the cylinders off it's important not to let the pistons in the upright position fall down so here i've got pistons one and four in the raised position just make sure they don't clatter down too hard and damage themselves at this point you can remove the cylinder gasket as you can see on my engine i've got a huge amount of debris that sat on this to avoid any unnecessarily falling down into the bottom casing just run a vacuum over it or clean this off finally in this video we're going to remove the pistons on each side there's two small piston pin clips i removed these with a small pick and a pair of needle nose pliers they are held under a surprising amount of tension so i do recommend wearing a pair of safety glasses when you do this they will need replacing so if they do ping off across the room don't worry too much you're gonna have to buy new ones anyway with the piston pin clips removed you can just remove the piston pins you can even do this using a small pair of needle nose pliers or i also found that a sharpie pushed through the rear of these removes them very effectively once you've removed two of the pistons you're gonna have to turn the engine for 180 degrees so that you can access the piston pins on the remaining two pistons [Music] and just because i wanted to see what sort of state they're in the pistons as they came out i gave them a quick clean and then just brighted them you can see here how quickly that carbon comes off and he ended up a lovely shiny top so guys that's probably a good spot to wrap up this video before we do let's uh take a moment to summarize what we're going to do before we get this engine running again first of all the top end uh looks pretty manky to be honest it looks like you do have a good clean including lapping all of the valves checking the tolerances and i'm also going to replace all of the valve seals with slightly higher spec ones i'll probably cover this in part three or four of the rebuild series i wasn't planning on rebuilding the bottom end but looking at sheer amount of debris that was sat on the cylinder gasket i think a lot of it will probably have ended up in the crank case it's not a small task splitting this so i do take the decision fairly uh heavily um but i feel like if i don't open that up and clean out any debris that's in there it's going to give me a lot more problems long term with the bike so i'm going to be doing that in episode 2 splitting the crank case and giving it a good clean through externally on the engine would definitely give it a thorough clean i'm possibly going to vapor blast it or at least i'll be cleaning off all the corrosion and painting the engine possibly polishing a few of the covers but i'm going to start on the rebuild in earnest so first of all it's getting new new gaskets seals throughout the engine it looks like these haven't been touched into the factory or certainly not in living memory so i'm definitely going to be replacing those i'm going to go through and check the bearings as i go make sure if there's any of those that need replacing i do that as i go and also i'm just going to check over the clutch make sure there's enough life left in it to give me many many years of hassle-free motoring finally the carbs are all stripped down and removed ready for vapor blasting i'll be doing a video showing those being split down and then a second rebuild video that'll be coming on the channel soon so if you're interested in seeing how i do the carbs make sure you hit subscribe guys that's about it for this video i hope you've enjoyed it i hope it's helped you out with something if it has really appreciate a thumbs up beneath if you've got any questions or any comments on these dual overhead cam engine rebuilds or the channel in general please do hit me a comment below i'd really appreciate it i'll get the next video as soon as possible pandemic pending uh if you want to be told as soon as it comes out do make sure you hit that subscribe button until next time take care of yourself and stay safe cheers

Channel: Letterbox Workshop

Views: 6,629

Rating: 4.9061031 out of 5

Keywords: honda, CB750, Honda CB750, Honda CB750 Engine, Honda CB750 Engine Rebuild, CB750 Engine Rebuild, Engine, Engine Rebuild, Rebuild, Teardown, Valves, Pistons, Piston Rings, motorcycle, service, maintenance, Honda CB, dohc, honda dohc, brat, barn find, renovation, CB, step by step, instructions, guide, how to, Cafe Racer, Tracker, Custom Bike, Restomod, Motorbike, CB650, CB550, CB900, CB500, CB450, CB400, Mechanics, DIY, Powder coating, Frame hoop, Frame loop, Welding, Weld, Bike shed, The Bike Shed

Id: toh_VRicADk

Length: 28min 26sec (1706 seconds)

Published: Wed Nov 04 2020