Honda Clone (GX390) Engine Rebuild - Low Hour Engine Dropped a Valve

[Music] hey guys welcome back so today we're working on this 13 horse Honda clone I recently pulled it off a gener gp6500 and I think you can tell why uh this engine was overs sped and as a result the valves started to float you know they couldn't get out of the way in time and the Piston just started hammering the valves until one of them broke and that valve got crunched you know between the piston and the head destroying both you know that said though the rest of the engine seems to be in pretty good shape and this one would be worth saving it only has 64 hours of runtime on it so my hope today is that by the end of this video we will have this engine up and running again so let me get you set up a little bit better and get going on this so you may have seen this engine already in another video and I did an engine swap basically pulling this out of the gp6500 and putting a good one in its place but in that video we did open the engine up and take a look at the internals and the bottom end is in great shape and surprisingly the cylinder is in very good shape too there is no scoring no damage that can be felt and there is plenty of crosshatch so this block block I would say 100% is good uh that said though I wasn't sure if I was going to be able to rebuild this you know luckily gener does stock and sell the parts we need you know we need a piston potentially a connecting rod aead two valves and some miscellaneous things but when I priced it out it came to about $430 and when you factor in tax and shipping it's closer to 500 and I can say with certainty that what ever generator this engine will go on is likely going to sell for $400 or less so buying the parts from gener doesn't make sense but I don't want to throw this away either you know I've taken apart a lot of blown up engines a lot of Honda clones and I've saved the good parts and I think I have the parts I need to put this together for about 20 bucks you know just the cost of a new head gasket a new sump gasket and maybe a few miscell things but I do have I guess one big concern let me show you that and this is the head that was on this engine you can see the extent of the damage that valve got hammered into the head you know this seat is destroyed obviously that valve is destroyed and this one although it's still attached I'm willing to bet it's bent and weakened so yeah this head is not good now I do have other heads actually for four other Honda clone heads that will fit an engine of this size I guess my concern was is that this valve cover is rectangular this is a Hemi head which in this case really just means the valves aren't going straight down they're actually angled so they conform better to the spherical shape of the head and the heads I have aren't like that but I think the bottom end is the same it's just the head that's different so let me show you the heads I have and what I'm thinking is we can just swap out the Hemi head for a standard one and this is the style head I have these are actually more common you can see the valve cover is quite a bit different and if I flip it over if you look at the top of the head it's actually not very spherical it's actually pretty flat and the valves are flat as well that said it has the same footprint as far as the ceiling surface goes and I've already test fit it and it fits on and bolts on just fine so I think we can swap the Hemi head for a standard head which is good news cuz that's going to save I would say close to $300 just by doing that now that still leaves the issue with the piston and I think I have one of those as well you know it's used but I think it'll work and this here is the Piston I have this was pulled from a GP 5000 also 389 CC so it has the same displacement it is a Honda clone just like this and I've already test fit this piston in the boore and I think it's actually a perfect match so we will double check that I think the next move here is to get this engine fully apart you know I cleaned up the inside a little bit you know there were some pretty big chunks in there but it needs a thorough cleaning so we'll take the engine cover back off we'll get everything out of the engine clean up the block and start putting this back together this just a piece of scotchbrite and a bit of WD40 taking off the high spots so that when this comes out hopefully it doesn't cause any damage to the oil seal just going to rotate this a little bit till the timing marks line up and then we can pull out the cam shaft and the lifters being sure to keep track of which is which uh the exhaust is the closer one and the intake the far one and we need to do the same for the counterbalancer we have to rotate the engine a little bit further and timing marks are now aligned so if you don't do that you might have issues clearing to get this piece out and then we're just left really with the crankshaft so let's get the cap off the connecting rod then we should be able to get the piston and the crankshaft out all right that one's loose let's get them both loose before removing either one I'm not sure that's going to work we're too close to the Gear so I'm going to switch out to a ratchet for things are looking really good this crankshaft is pretty much perfect the main Journal looks great the journal on this side is good and the bearing perfectly smooth no noise at all so the crank 100% good the counterbalancer also looks like new so I'd say that is a good part and the cam shaft you know the lobes look to be in very good shape you know I don't see any issues there the compression release is still intact and you know there is a piece of metal right there that's part of the Piston so you know all these parts do need to be cleaned but they they seem to be good and well lastly we have the Piston which we know is bad the connecting rod though actually seems fine as well as the wrist pin so we might reuse that or you know I guess we have a plan B we could use that connecting rod now the thing I'm kind of debating here is what to do about the Rings these rings are used so we could get some new Rings hone the cylinder and know we're good to go and usually you do replace Rings you know they are a wear item but this engine only had 64 hours on it you know these rings have only just seated in the cylinder the cylinder is in fantastic shape like I don't think we need to hone it and I don't think we need new rings so what I'm leaning toward right now is just transferring the Rings over and calling it good so let's actually just get these rings off now we'll drop them in the boore we'll measure the end gaps and if things look good then I'm going to use these rings on that piston just double check the diameter of this bore we're close to 3 and 1/2 in and A good rule of thumb is about 3,000 of an inch end gap for every inch of boore so in this case we're looking at a minimum end gap of 11,000 and a safer number would be 4,000 per inch so that would be more like 14,000 end Gap minimum it can be larger of course you lose a little bit more compression burn a little more oil but if we're close to you know 14 or 15,000 I'd say we're pretty much perfect I can tell already that in gap's pretty tight uh I'd say close to 15,000 so let's start let's start with a 15,000 feeler gauge and no that does not fit so let's try a little smaller uh maybe a 13 yeah and a 13 fits so we're somewhere between a 15 and a 13 which is basically brand new so this ring has minimal to Nowhere uh let's check the second ring and the second ring it's normal actually for it to have a little bit more clearance on the end Gap than the first ring so we saw between a 13 and a 14 actually between 13 and 15 on the first ring so I'm expecting this to be a little higher and just looking at the Gap I can see that it is higher so maybe closer to 17 or 18 so let's start with I guess an 18 yeah an 18 fits but there is a lot of drag so that ring I would say is 18 which which is good so these rings I would say can be used so now starts the fun part of cleanup so I'm going to get this oil sensor loose so we can move it out of the way that way I'm sure there's chunks back there which we need to clean out and actually this whole block I'm going to soak in soapy water and just get all the little bits out of here yeah you can see all those chunks right behind the oil sensor and another place they like to hide is actually In this passage here over on the other side that's the bolt for draining the oil out so I will pull the bolt and just make sure you know we'll blow through that with air make sure it's clear and no fits a metal remain that those are in there all right that one's not budging yeah these These are kind of rust jacked in place I think it's going to be a problem but they need to come out you know we can always buy new ones I think I have others so I'm not overly concerned about saving these locating pins I've never had pins in there so tight so obviously these are not going to be savable but now I'm just more concerned about how to get them out without causing damage I think a slide hammer potentially if I can somehow adapt it to get in there so let me double check what I have [Music] what nothing hm [Laughter] yay never had to work so hard for a dowel pin so one down one to go I think the key there was kind of folding over the end so that this could grab it a little bit better this is meant to pull ball bearings from a blind hole and on the other end of this tool is a lip that's supposed to go behind the ball bearing so if it can't catch on anything then the tool just comes right out so we'll just fold this over like we did the other one and hopefully this one comes out as well for there we go the engine Block's been fully cleaned all that gasket material gone and the block washed out with soap and water you know everything's been reoiled and the same has been done for the engine cover so these two things they are ready to go also the crankshaft the counterbalancer and the cam shaft have been cleaned and oiled so those are all set so we are getting pretty close really the big outstanding item here is getting the Rings moved over so before I do that though I do want to run a few more checks and just make sure that that piston is going to work and one thing to note you can't just swap the head type without swapping the Piston as well the Hemi head Honda clones use a piston that is perfectly flat on the top and if you're going to use a standard head you need to use a piston that is dished like the one we're going to use anyway I've been doing some checks between these two Pistons just to see if the important parts are the same and so far most things are checking out I did find one problem I'll show you that in a second uh but first I checked the diameter and this one is actually a few thousands wider than the one we're going to use so I think that'll be okay I'd rather have it a tiny bit smaller than the other way around uh the next big thing is the skirt the skirts on this piston don't go down very far whereas if you look at the Piston we're going to use they go down I would say a good half inch further so that should be okay but I'm thinking I want to Loosely assemble the engine and just rotate it over and make sure that there's not going to be any interference and at the same time we can also check the deck height you know when the Piston's at top dead center it should be exactly at the same level as the deck you know if it extends too far or not enough then we know we need to dig in and just double check the connecting rod to make sure that it is the same size now the one thing I did find that is a problem actually has to do with the Rings you know I wanted to reuse these Rings because these are the ones that go with the cylinder and if I'm not going to hone it then these are the rings I have to use so I checked the measurements both on ring one and ring two so ring one actually comes in at 1 millimeter and ring two comes in at about 1 four 1.3 so what I wanted to see is that the Rings out of this piston have the same measurements you know otherwise we can't use those rings so when checking ring one it also comes in at 1 to 1.0 millim so top ring can definitely be moved over the second ring on the bad piston was 1.3 1.4 and on the Piston we want to use it's actually 1 mm so that second ring isn't going to fit in the good piston so we need a new set of rings which means we need to hone the cylinder and clean the block again so I actually do have a new set of rings that we not used for another project so I was double-checking these and I think we're going to be okay you know ring number two was the one in question and when I measure it here we're at 1 mm and if I check the top ring that also should be 1 mm and it is so this new set of rings I think will be fine uh we are going to have to check and potentially adjust the end Gap so yeah let's check the end gaps now on these and then I'm thinking we would will Loosely assemble things and just make sure that everything is going to work out as it should all right let's check the number one ring first that Gap looks pretty good I would say it's probably around a 15 or a 16 so let's start with the 15 that fits let's jump to 17 17 fits but it is quite tight so I'm thinking it is a 17 uh let's check in 18 yeah 18 doesn't fit so the top ring should be fine you know if it was less than I'd say 11 I'd be very concerned but the way it is is good let's check the second one and that Gap looks a little bigger let's try a 20 yep 20 does fit and 23 does not fit so it's probably around a 21 uh which is fine the second ring Gap is usually a little larger than the first so I think these Rings will work it probably doesn't matter but I'm going to use the original connecting rod since that has been running on that crankshaft it should be mated well with it already so we're just getting out one C clip and this wrist pin should I say should slide out might need a socket of the right size to tap that through for just make sure it's in the groove el else the engine isn't going to run for very long yeah I think we're good for I think we're good the skirt of the Piston it's shaped to clear the counterweight so I think we're good I'm just going to add the cam shaft to make sure nothing interferes with that I think we're good that is perfect we are at top dead center and the Piston is in the right spot so I think we can hone the cylinder get the Rings installed and put this thing together this cylinder doesn't need much so it's just going to be a light quick hone [Music] [Music] I've already got the oil expander ring installed and now I'm going to put on ring two followed by ring one now these didn't come with any instructions as far as indicating which ring is which and which side is up but it does matter and the rule of thumb is that if there is a marking on the ring like we have there then that should be facing up and the ring that has the Chrome sometimes it's all Chrome you know in this case it's just a chrome corner you know that is the top ring so we'll start just by getting the second ring on and then the top ring and that's it the Piston is ready uh the Rings are clocked I have the top one over to the right the second one 180° to the left and then the bottom expander ring that's actually three rings and those I have staggered so the center of the expander ring is right there and then we have the top and the bottom ring about 20° offset from that so the Piston is ready I say we get that installed we'll put the bottom end together get that closed up and then move on to the Head for put a little bit of thread Locker on these bolts that hold this oil sensor in place for I don't have a manual on this engine when in doubt this is a clone of a Honda GX 390 so using Honda specs should be pretty safe you know Honda calls for 120 inch pounds on the cap so that's what I'm going to do I'm going to bring it up halfway and then finish it off for all right we need to line up the timing marks there's one right there in the small gear and the other one is right there so we are off and that that is perfect and on the counter balancer there's a timing mark right there and that's going to align with the one right there on the larger gear like that for for we're getting close and it's tempting just to install the head I'm sure the valves are seating fine I don't think this head had a whole lot of hours on it but since we have access let's decarbon this you know we'll pop the valves out real quick lap them in and of course clean up this surface [Music] yuck that's oil that's pretty nasty so yeah I might change my mind on this one this was the cleanest head from the outside but the engine that this came from was not in good shape I don't know if you remember it but it was the I think it was a GP 5500 where the oil down in the sump was probably the worst I'd ever seen and I thought the top survived but yeah I mean this could be cleaned up for sure but I have a few others to pick from so I think going to set this one aside we'll choose a better one all right head number two this one isn't bad actually it'll clean up really well uh but let's get the valve cover off and just make sure or we don't have any [Music] surprises better A lot better for for for for so before I lap these valves in I'm going to clean them real quick just with some scotchbrite and a bit of WD40 you know spin it in the drill and just let the scotch Sprite do the work e [Music] [Music] the intake valve feels pretty good so it only needs a tiny bit of lapping [Music] it looks pretty good we got a nice line going around and a quick test is just to drop the valve in and put some pressure on it try to spin it it shouldn't spin if it does you might lap it just a bit more in this case the intake is fine so we'll get that out and do the exhaust exhaust valve lapped in real good and unlike the intake the exhaust did spin pretty easily before the lapping and now it sits in there pretty well so let's get the valve springs back on and bolt this to the engine make sure the flat side of that retainer faces down toward the rocker [Music] not sure what to think of this gasket usually I use ones like this and well the kit I ordered came with a metal one so we'll give it a try you worst case we can always swap it out for yeah we're at the point now where I'm getting excited to hear this engine run so I'm going to put some oil in now before I do something stupid and try to start this engine without any oil and this is just 10w30 conventional you don't want want to use synthetic until the Rings have seated I want to get the push rods in next and set the valves but first we'll do the flywheel and probably the ignition coil it'll just make it a lot easier to rotate the engine to top dead center with ignition coils technically you can mount it either way and it will go on just fine but if you mount it the wrong way it may not spark and the timing will be off you know in this case it's not labeled which way is which but on Hondas and Honda clones this kill tab faces down so that is kind of the Dead Giveaway so we'll just connect the wire attach it to the clip and then we'll secure it with two bolts and then set the gap so I need to torque down that flywheel nut and I want to do it now before I install the push rods cuz without the push rods the valves are always closed so right now the Pistons at the bottom of its travel we're just going to fill the cylinder with rope which will lock it up and then we can torque down that flywheel nut now I have some conflicting information as far as what the torque should be you know I saw one Honda article that said 83 foot-pounds another one said 125 and I also checked the rotto service manual and they say 98 so I'm going to go with 98 cuz my torque wrench tops out at 100 so 125 not an option for [Music] swapping that head from a Hemi to a standard definitely isn't as simple as just that you know as we've already seen we had to swap the Piston as well you know in our case at worked to our favor because that was the only piston type we had was for a standard head now we're at the point where we need to get the push rods in and looking at the push rods that came with the Hemi head they're quite a bit longer than the ones on the standard which is on the right here so I'm assuming we're going to need these push rods rather than the Hemi push rods but let's just test fit one of each to make sure this here is the longer push rod from the Hemi and yeah I think that is too long let me just rotate the engine make sure the tap it is closed and it is so when it's closed this rocker if anything should be level with the surface if not tipped back a little and in this case we're already tipped forward like it's trying to open the valve so when the valve actually opens it's going to continue quite a bit further in that direction and the angle is going to be too steep so the Hemi push rods I think are out and we'll stick with the shorter ones for the geometry looks pretty good but I realized I forgot something and this is something that I think a lot of people forget or don't even know about and that's the Rotator cap you know not all Hondas and Honda clones have it some of them have no Rotator caps some of them have just one on the exhaust like this one and some have a cap on each and the sole purpose of it actually is to put a little bit of air gap between the valve stem and this Rotator cap so when The Rocker actually pushes down it's pushing more on the retainer and the valve is allowed to float a little bit in the retainer which loosens it up and then it can rotate minimizing wear to that valve the easiest way to adjust valves on this engine or really any engine is just to rotate the crank until one of the valves is open and the other one should be closed so at that point you can d in the Gap that you need you know in this case I'm aiming for 7,000 so we'll get it close which is right there and then I'm going to add this nut right here this is what locks the adjustment in place you basically tighten these two against each other and then neither one will rotate but as you tighten them it takes out kind of the slop and the thread so even though we're right at 7 now once I tighten this usually that Gap will close so what I like to do is snug these up which will take out a lot of that slop when I say Titan just snug them so that you can actually still make adjustments so right now while we were at a seven and see now a seven no longer fits so we'll back that up a bit but you see when I do that actually this nut didn't turn so it is kind of locking up so I can only turn it so far before I can't turn it anymore and actually that is pretty much perfect so let's just make sure it's snug and by snug I mean tight and yeah that one is good so rotate the engine till the exhaust is fully open which is right there then the intake I'm going to set to 5,000 and same procedure here that feels pretty good yep now we lost our clearance we'll back that up just a bit and both nuts are spinning so it's not going to lock us from making the adjustment like the other one did all right it's too tight feels pretty good and there was a lot of slop in there so I'm to bed it's tight again yeah is actually zero lash right now for perfect another side effect of swapping the head is that the tins both the top and bottom from the Hemi head don't fit you know we have to use the standard tins and I think even the blower housing it's a little bit different in this area so we're going to have to swap that out as well spring tension feels pretty good but I don't want this running at 3600 RPM at least not to start with so took some of the tension off it might take a little bit more you know I'd rather start this at a lower speed and once we're sure things sound good we can bring the speed up some as far as the wiring goes on this machine it's pretty straightforward we have this wire right here which runs over to the ignition coil if this wire is grounded out on any part of the engine then spark is killed and the engine shuts down so we have two switches to essentially connect this wire to ground the first one right here with two wires one is connected to ground and the other one we need to connect to the coil and like this when we turn the switch off it'll kill spark and the second switch is inside the engine that is the low oil switch the yellow wire comes out connects over to the low oil module now we have a black wire coming out which is what actually kills the spark so we're just going to connect that into the same circuit so now either one of these can shut the engine down we're getting pretty close just Fuel and exhaust so I dug around on the carb bin came across this one I labeled good so I think we have a winner now this carb isn't perfect for this engine meaning we have a fuel solenoid this engine can't control it uh but it doesn't matter this is normally open so the fact that we can't connect the wires shouldn't impact its performance and the second issue is this choke is for an auto choke which again this doesn't have so we're going to have to control this manually uh but the rest of the carb should work just fine at least for testing so before just bolting this on you know I want to double check the governor calibration because this head is a different size and the governor was calibrated for a different head which likely means the carb was in a different position so the way to double check this is to set the throttle plate in wide open throttle keep it in that position Slide the carb into position and then move the governor arm in the same direction now the spring is already holding it in wide open throttle you know that's idle that's wide open throttle so like that both of these are wide openen throttle and the 90° on the rod should align with the hole here where it installs and I think you can see the problem here we're a good I don't know inch away so if I were to install this as is the governor would not be able to slow this engine down it would just run at wide open throttle until the engine blows so we need to loosen this nut reset the governor calibration and then finalize the carbon inst stall and just make sure you have that pin on the governor shaft without it you could get yourself into trouble because when you loosen this nut up the only thing keeping this shaft from falling into the engine is that pin and it actually rides on the outside and a channel on this shaft so if you push down hard once this is loose you could actually pop the pin off and then the shaft falls into the engine if that happens the only way to get it back is to open the engine and retrieve it that is on there tight there we go the other thing you need to figure out here is which way does the shaft move which way does it rotate when moving to wide openen throttle so when I move the throttle plate in the arm to the right this shaft rotates counterclockwise so that is important because once we connect this to the carburetor we want to hold the arm in the wide open throttle position and at the same time rotate as far as we can to the wide openen throttle position which is in this case counterclockwise for I hate to say it but I think the adjustment I just made may not have been absolutely necessary you know now that it's been made I can see things operate fine but in the wide open throttle position this arm is usually coming more straight out and instead we're at an angle so that got me wondering is this Rod shorter than standard clone rods and the answer is yes the Hemi Governor Rod is shorter than the standard head Rod so I'm actually going to put the correct part on we'll reset things again and move on for for this anti- Serge spring it is kind of bent up you know it should be replaced got some on order but for now it'll be fine you know as long as it applies some spring tension doesn't matter the shape of the spring it'll work just fine so now that we have the engine back together I'm going to do a quick compression test this has a decompression system so 60 PSI is usually the average that I see you know that could be plus or minus 10 psi so anywhere between 50 and 70 would be perfect so let's pull the engine over and see where this one comes in at beautiful and we're at 70 PSI so this engine should run quite well I would think so let's add the plug bit of fuel we'll see if it starts so what do you think is it going to run I think so but I've got to admit you know this makes me a little bit nervous you know I have never done a Hemi swap to a standard head and I've never seen anyone else do it so you know although I think I did it right you know until it runs we won't know for sure so to that end I've plumbed in the fuel it's turned on we don't have any leaks so let's close the choke turn on the ignition and we'll try to start it now assuming it does start uh the engine speed is going to be a little bit slow I did take some of that tension off so if the engine sounds good we'll increase the tension a bit and just see how it does I've got to admit this one exceeded my expectations I went into it not knowing if it was possible to do a Hemi head swap with a standard head and of course as we just saw it is possible because this engine it is running quite well it started first pull I was able to turn the choke off right away and the engine sounded great no knocks no funny noises it was running nice and smooth so I brought the speed up close to 3600 RPM and things kept running just fine so considering where we started you know this was a blown up engine with a hole in the Piston a damaged unusable head with a broken valve and likely a bent valve and of course if we wanted to fix this correctly using gener Parts it would have cost $500 and instead we piece together a machine with the parts on hand for the most part you know I did have to buy a gasket kit that was $4 and of course the set of rings that was $20 from eBay so in total I had $34 in parts and a bunch of time and the end result well I'd say it turned out pretty well so you I guess the question is can it pull a 6500 watt load you know this is a 13 horsse engine and that's something we're not going to find out today you know I don't have a Honda clone that needs an engine right now so this engine's going to go on a shelf but you will see it again hopefully soon so I hope this video helps someone thanks for watching

Channel: James Condon

Views: 60,743

Keywords: 389cc, 390cc, 420 cc, Alternator, Compression Test, Dropped Valve, End Gap, Engine Rebuild, Feeler Gauge, Fixed, GX390, Generac, Generator, Governor Reset, Head Gasket, Head Swap, Hemi Head, Hertz, Honda Clone, Hone Cylinder, How To, How-To, Lap Valves, Load Test, New Rings, Piston, Push Rods, Rebuild, Repair, Small Engine, Timing Mark, Timing, Troubleshooting, Valve Clearance

Id: 7nIj6ikWF3o

Length: 89min 21sec (5361 seconds)

Published: Thu Apr 25 2024