Low compression CB750 engine teardown. Found the problem.
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- Опубліковано 28 вер 2024
- Hope you guys enjoyed this one. Let me know what you think in the comments.
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Just a few quibbles with the terminology used in your commentary:
The "top" ring is properly called the compression ring
The "second" ring is properly called the scraper ring
Yes, the "third" "ring" is called the oil control ring and consists of an expander in the middle with rails above and below it.
As well, after honing the cylinders you MUST use clean white rags, preferably something soft like cotton (old clean white tee shirt material that's 100% cotton without silk screened stuff on it works great) to clean the cylinder bores of all the grit from the hone stones AND the cast iron powder from the liner surface itself. Wipe the bore with a cotton rag dampened with mineral spirits (NO WD40 or similar lubricants) and then toss the dirty rag. Repeat this process until your last rag will not show any black stuff at all. You'll be surprised at how much rag material you can use just to ckean ONE cylinder bore. Your whole engine will thank you for taking this extra step of getting rid of all that abrasive crap.
As to installing the block and coaxing the pistons/rings into the bores: you really should thoroughly bathe the rings with engine oil before trying to get them into the bores. You'll find that things go much easier.
It would also be a great idea to lube ALL the cam bearing surfaces AND the lobes with engine oil or "startup lube" before installation.
Just read your comments, after I had posted mine, and agree entirely, but I think this guy is doing a great job and if our comments are valid, then it should enhance the Video. However, it must be remembered not to 'carp' at people from the side-lines.
I had the pleasure of attending and graduating (youngest to grad age 16) from American Honda Midwest Service school back in 1970 right after the Daytona win. The class was held in Bob Hanson’s Race shop in Racine Wisconsin. My instructor was Bob Jamison who prepped the winning 750. He was a real stickler for detail and this is what I learned from his philosophy. You did a great straight forward job however what you missed was...the troubled cyl probably had rusted (at least) the intake valve. If you’re not intending on inspecting the valves, do a leak down by pouring solvent in the intake and ex to see if it’s getting past the valves. The cam tension rollers get brittle and under all circumstances be changed. The rubber compound on the knockoffs are not near the original Honda part.
The valve seals also get hard, and while you’re in there, it’s an evening job to pull the valves, lap them in and put new seals in. Make sure u check and lube the stems.
Sure you did
Jamison grad 69
always a good idea to remove the valves and lap them in by hand.Particles of rust can sit on the surface of the seats and hold the valves open slightly.Its just peace of mind,and saves having to strip the engine down again.cheers Graeme from New Zealand,enjoy your programmes
Thanks, very nice to watch.
Having already disassembled the cylinder head, you could have taken the opportunity to grind the valves too...
Great call choosing to do the top end rather than just engine swapping. This is much more interesting and helpful.
Glad you liked it
1
I'm
@@ClassicOctane taught me a bit about engine timing! Thanks!
"Im not going to do a 'How to...' video, this is more of an overview"
...Proceeds to do an overview video 10 times better than 99% of 'How to's!' Lol. Watched every bit of it and I dont even have a 750, great vid as ever! Excellent job mate.
Thanks Alan
Mate. I've been watching you for a while now, and I must commend you on your entire approach to your content. I've considered trying it myself, but the whole 'talking to camera, explaining stuff, then editing and publishing these videos, along with actually fixing a real life motorbike, is a bit of a handful!' So you, my friend, are something else. Just thought I'd say something positive (and truthful), cuz we all need that shit now don't we.
Lazy Bones well said!!!👍
Agreed!
Thanks! I really appreciate the kind words.
A - Im a strong believer in cleaning up the engine prior to removal and conducting a leakdown test on it at that time as well . In addition if it wasnt a runner I'd be tearing down the bottom end and checking bearing condition and clearances . Also the bore & pistons should have all been measured . Minimum piston - wall 0.001 - 0.002 clearance . Ring end gap top 2 = 0.007 - 0.016 . Oil ring = 0.012 - 0.035. little tip ... you can increase the taper prior to boring / honing ... makes installing the pistons a snap. Cam timing . I always check again AFTER cam chain tension has been set . Use assy lube cam bearing surfaces .Your videos are well done.
Pistons with jammed rings can make the bore go oval so measuring is a must before deciding what's needed.
The beauty about SOHC Hondas (and Z1 Z900/1000 Kawasaki's also H1 H2 triples) is that there is so much after market stuff for decent prices. Their continuing popularity and sheer numbers sold, especially in the U.S means its commercially viable to mass produce parts. I'm into 80s Japanese stuff, but the 2 year product cycle, often with complete redesign, means finding parts for some bikes a nightmare.
Piston Rings are probably set to have the gaps away from the front & back of the cylinder because that would be where the most pressure is applied by the rod/crank as the piston moves through the cylinder.
This is also my understanding.
I was taught as an apprentice that the ring gaps go on the opposite side to the thrust side of the piston.
I knew there had to be a reason for it.
I hope no bits from your exploding piston ring ended up in the crankcase! I would probably have stuffed a rag in each of the crankcase holes for the pistons as I have butterfingers anyway ... great video by the way - thanks!
I thought the same thing, my luck, one little piece would've went down into the bottom.
Taylor you do great work and then present it well. Couple things I’ve learned to do. Permatex or something under the pucks or they leak. Torque cam towers and caps or risk screwing up threads. Red loctite on cam gear sprocket. Big problem if they loosen up. Torque head bolts and do it again in 24 hours and again in 24 hours until it holds a constant torque. You can put a weldless frame kit in allowing you to do a top end job w/o removing the engine. You can always weld the frame back together. Keep up the good work.
Yes would defo agree with the use of loctite and re-torqueing the head after a setting period
Good suggestions. Thanks!
Just allow the camchain to drop into the crankcases, fit the cylinders and cyl. head , then retrieve thy cam chain useing a telescopic magnet or a piece of hooked wire, ... makes life so much easier.
Just a perfect explanation which we owners of cb's thank you a lot. Thankyou master
Very good instruction video ! Thank you !!! Greets from Belgium (Europe) 👍
Good video. Thanks for making it. CanI suggest next time add a comment on how to test now well the valves are sealing. Such as using a flash light to see a gap. Or gasoline/kerosine in the valve to look for drips. Not that hard to lap the valves since you are in there.
Darn, wish i watched this a year ago. I did my upper gasket because my 550f was leaking oil. I discovered massive carbon buildup on the cylinder heads and the valves. I sprayed for two days sea foam spray, brake cleaner, carb cleaner and some came off but it was a centimeter thick solid caked on carbon buildup. Then i lost my job and could afford to order the full kit or many of the tools i wish i could have had. It took me a lot of time and a lot of brass brushes i had laying around to break down and clean the carb. The rings seemed ok so i left them because i was losing money. I got it all back and running but wish I could have done a better more thorough job. Now im selling mine because I need the money. But i put a lot of time into restoring it from the previous owners lack of care.
Use oven cleaner for carbon build up
When I still believed that a compression test was the most useful test to figure out the status of the top end of an engine, followed by a bore scope, someone suggested a pressure test. I thought he meant compression test and just misspoke.
But he patiently explained how pressurising any cylinders that are down on compression, will quickly reveal WHY it’s down on compression.
If the air escapes through the exhaust, it’s the exhaust valves that are at fault.
If the air escapes through the carburettor or inlet manifold, it’s the inlet valves that are at fault.
If the air escapes through the oil filler, it’s the piston rings that are at fault.
I have literally NEVER seen this advice on any problem finding vid, engine rebuild vid, bike or car vid, or forum anywhere.
This is obviously great advice, but how come no one ever seems to be aware of it???
thaks a lot for all the info. i think the ring gap not being at the forward or rear of the pistion is because there's some force fore and aft as the pistion mooves up and down which makes the bore oval/oblong over time.
This brought back very old memories. The only thing I'd have done differently is pack old socks/underwear/t-shirts into the barrel holes under the pistons before trying to take rings off; I'd put them there anyway just to stop things getting into the motor. As noted, rings are brittle; the last thing you want is to have to tear down the motor because a piece of piston ring disappeared into the belly of the beast. Many, many years ago, a pal with a 69 CB750 bought a new Yoshi cam complete with new cam supports and a full gasket kit. Missing from the kit were O rings for the oil lines to the head so he went to a local parts store and bought O rings. They were too big and squished when the head was torqued down, significantly reducing the oil ways. About a mile down the road on the rebuilt motor, the new camshaft seized. Very sad.
I see you start all four pistons in the cylinders at once... I start the middle two first then the outer ones and that seems to work well for me. good job on the video and it looks like you do good work. great to watch ...you are a natural teacher.
Rings are constantly spinning in the cylinder bore. Clocking them is nice for first start but definitely not a requirement.
Valves spin but I don’t think the rings rotate. Although my 2 stroke Fantic motor had pins in the lands to stop the the ring gap/ends rotating into the transfer ports
@@johnholmes5674 worked for Paccar engine on a project to find out if ring alignment matters. Turns out it doesn’t. This was for diesels but I’m confident it’s the same on gas engines.
Why wouldn't you rotate the crank until just two pistons are up - and get those in and then rotate it 180 deg. and deal with the other two?
I may be wrong, but it seems to me that working with only two at a time would be easier than wrestling with all four at once.
The weight of the cylinders will push those top two down. This way all the pistons are as far down as they can go so they wont move on you. You could support them with some pieces of wood though. That would probably work out pretty well.
Very methodical, low key presentation. Well done.
Great information. Could you offer an explanation on why you didn't take the opportunity to lap the valves on at least cylinder 4 please?
No need. They were sealing fine. I tend to only do what's necessary otherwise you can introduce more problems than you fix on an engine that's 45+ years old.
Absolutely love your content on the Honda cb’s. Trying to find a 70’s one right now to build one, absolutely love the sound and how much you can customize the look of this bike 🙌🏼😌
Awesome video! Helps a lot to visualize what I need to do when it's my first rebuild. Keep up the videos on the cb750. Can't wait to see the next ones!
Thanks, will do!
Great video as always but, damn, I get huge workshop envy :-)
CB750 problem SOLVED! ....Convert it to electric. haha
Love the video, brother. You know your stuff and always a pleasure seeing good dudes wrenching.
Heaven forbid the EV cult!!!
Well done Taylor, you've saved another engine and it was good to see what was wrong with it, the video made good content .....👍🏴🇬🇧
Thanks
How do you?
Know you have the right rings without gapping them first without physically checking the gap which means you've got to clean the cylinders hone if necessary. And then insert the piston without the rings on it so that you can get the ring flat level and check the gap at the end of the rings. Each bike has its own specifications for that gap.
Finally rebuild the engine..
Your new Fasteners SS ,watch that you do not get galvanic adhesion with them going into aluminum..can happen especially with the aluminum that Honda uses. SS isn't always the best choice.
Very good in explaining everything step by step ! That is very clever of fasting the engine to the engine stand
Can you show how the engine is mount to the stand and fabricate the frame to the engine . That would be helpful for us . I have a engine stand and trying to figure on how to attach a cb550 engine to the stand .thanks and keep up the good work !
You stated that you didn't want to use anything aggressive on your aluminum cylinder head and then went at it with a green scotchbrite. Green is aggressive and will remove metal.
I hope that when you finished you got a good seal on your head gasket.
You can score the bore if you have gaps front and rear, not over the gudgeon pin either or you could theoretically snap the end off.
For a video that is not how-to, there is a lot of how-to. This is a great look at the process, and thank you for sharing.
Hey, I bet it would be a REAL bummer to get the cylinder block and head on, look at the assembly bench and notice the cylinder base O-rings you forgot to put in. :P
Did you use anti-seize on the SS fasteners? That is a must do, since SS fasteners in aluminum will cause galling and/or seizing. Is there a reason why you didn't lap the valves? I would have replaced the valve stem seals as well.
fantastic vid. I put a big bore/big cam kit on my Grom clone a few months ago and it was nice seeing it's pretty much the same process for this give or take 3 cylinders 😂
This is very helpful since I'm planning to eventually do a top end rebuild on my 78 CB750K!👌🏽
Go for it!
I know it takes energy to explain wuch is highly appreciated because of my inexperience thnks
The best man! Go Classic Octane!
Tec tip for you , CRC gasket stripper dissolves carbon .
What’s happening with the lockdown triumph?
Excellent video. I may have to do all this to my K6 one day. Also, I noticed I've got the same boxer t-shirt that you're wearing. So I'll remember to wear that when I do the work....for good luck 😌👍
Your soundtrack is super chill. Is it Kruangbin?
Hi from the UK. I have a 1972 CB500/4 K2. Is the process of teardown substantially the same as for your 750? I found this to be a really informative and excellent video. In many years gone by, I used to rebuild many 100s of Rover V8 engines and I have always used some type of lubricant, either oil or Graphogen on all bearings and piston rings during assembly. It was just my way! With the problem with No 4 cylinder, did you (off camera) check whether the water ingress, which had clearly occurred, had got to the No.4 big end or the crank in general and the oil pump as well? I have subscribed and will be working my through your library. Excellent work.
The ring gap shouldn't be on the thrust side but as you placed them - to either side of the thrust sides
Cool...you made it look easy..thanks for posting
Nice Vid, however, I have a DOHC later model 750 and was looking for some info. Good vid and read some of the comments of how to not screw it up all worth staying for the tips.
how did you know what piston rings you needed before you script the engine. i wonder because it could be standard or reboard.
Awesome video! Very informative and explained well! Great job👍
The cylinders and head, piece of cake. But the gearbox, that's like looking at all the parts in an old mainspring watch. No thanks.
Great job and the video surely will assist with my head removal
Good to see that even a pro like you just ‘fiddles’ the pistons and rings in the cylinder. This process made me a bit insecure on both my CB350f and 400f top-end rebuild. It just seems so uncertain if all rings are seated right, even when logically they have nowhere else to go.. I also have a habbit of drowning everything in oil before installation, I guess out of anxiety of ruining things upon initial (dry) startup. Thoughts on that?
Sounds good to me
I prefer to put them in dry. I think they seat a little better that way. It's all personal preference though.
No assembly lube on the cam holders? All engines need plenty of lube help on the first start after any rebuilding is done so as the cam bearings etc do not run dry waiting for the oil pump to push all the air out of the oil ways and get oil up to the cam bearings from inside the base cam bearing. Just pouring oil over is not good enough lol. Look into assembly lube as it is a little thicker than oil and protects all of the moving part surfaces until the oil pump is pumping oil up to the head properly. Just an FYI Otherwise very enjoyable to watch.
Nice easy video, but I thought you'd lick the valves back in, just in case, while you were that far apart.
Thanks for a fantastic video. Learn alot every time I watch something from you. I have one request: Can you please go through a gearbox on a CB 500 Four. I have a problem with my 3rd gear. It’s jumping out all the time and I don’t dare to open up and see what the problem is. What do you think? You’re the pro! Please help! 😊
43 minute long video... hellll yeah
you mentioned torque specs... all of the bolts and nuts have specs for tightening... after awhile you will see a pattern with certain size bolts and type of threads and material involved.
Great technical lesson.
that was painful watching you trying to get those pistons in. lol
Surprised you did not put a drop of oil in the bores when you put the barrels on they looked pretty dry .. sohc go.
Great workshop.
Thank you Taylor. I now have more confidence in doing the top end on my CM400T! Question, do you put any coatings on the gaskets to help them seal?
No coating should be needed as long as the surface is nice and flat
Wouldn’t assembly lube have been helpful where reinstalling the cam shaft?
should you have oiled the camshaft bearings when you fit it
How does water get into the cylinder on an air cooled engine? And only on #4 cylinder. If water was in the fuel, I would expect similar findings on all cylinders. Elbow grease works great for cleaning!
PUT HI HEAT OIL RESISTANT black rtv on those “hockey pucks” !!!!
They get brittle from heat and will start leaking oil!!!! through the fins on the head …everytime
How can you buy new rings when you don't yet know what size they are? Or whether the bores are shagged?
No oil on the pistons no assembly lube on the cam bearings?
Great work!
Thanks!
How do you mount the engine to the motorcrane? What parts and where to get em. I just took out my first 4 cilinder from a CB750f, they weigh insane amounts. the motor is on the ground but need to be able to work on it. Wanted to buy a moveer for the engine like you have, but the connections are not suitable. Can you share your setup perhaps ?
Quick question, i see that there was still top ring witness marks in the cylinder bores, even after you lightly honed em, any issues with blow by ? Or any other issues ?
How cone you didnt clean em out all the way ?
Why wouldnt you squirt some Oil on new Rings or in the Bores???
I wonder why they didn’t put a wheel on the end of the cam chain tensioner
Hi bud, that was very helpful, I did a dry and wet compression on my bike, the dry compression was lower the wet compression, the results was 75psi on 1-2, I going to do a top end rebuild, the bike iam talking about is a Kawasaki er500 '03', yah that was vary helpful, I also watched the video on the valve head rebuild doing the valve stem seals, silly question, can you loses some compression by the value stem seals has well??
Keep the gd work bud
You won't lose compression through the valve stem seal but you will from the seats. I personally wouldn't strip a top end without doing a valve job while I was in there. Simple on a 2 valve head. Note that if the seats need anything more than a light dressing then best use a proper valve seat cutter. It prevents pockets forming.
Did you have to mod that engine stand to fit the mx engine?
Might as well deck the head and cam and spring it while you're there?
Top job mate
Thanks
Hi,
I have recently installed my CBX 750P engine. all parts are new and original. I changed Crankshaft, Main bearing, and Conn. Rod Bearing, pistons and rings, Cylinder, Cylinder head, Valves, Seals, Cam Shafts, Arm valves Rocker, Adjuster Hydraulic Lash, and all Gaskets and so on. The first start was very smooth. The engine is running without any problem and noise. But I think a hidden problem occurs. When I check the cylinder compression I find 95 PSI. In the workshop manual, the value must be 171 (+28,-28). I have just rebuilt and no break-in. The 95 PSI is normal value?
Will the compression value increase up to 170 PSI after the rings seat?
I have checked the cylinder head leaking(not leaked- The cylinder head is new) and measured with 2 different gauges.
--
Best regards and stay safe,
Excellent
EVER THINK IT COULD BE VALVE SHIMS?
What's your manual of choice? Haynes?
Second guess it's a valve issue. Not seating.
A great video.....
Where do you get the stainless hex bolt kit?
What happens Taylor if the T chain comes off the bottom sprocket, can you get it back on from the top, ie no need to pull bottom off? With Pajeros I hear its a big issue if it comes off while doing top end work. Thx Tim
You can just lower the chain a little and move it around until it engages the lower sprocket. Not a big deal at all.
your awesome man
Thanks Mike
No assembly lube????
Exelente muy bueno
Great, except for one minor detail, and I have not finished before writing this. No problem on earth just exists. So that being said. All the way through I was asking myself what caused that? Then I watched the rebuild but was still asking, what caused that. Then you said the magic words, "It looks like this was done not too long ago...Red Flag!!! And so it will be a short time and need done again, why you ask, because you did not fix the problem, you did a great tear down, yet did not magnaflux the head, have the valves replaced, might as well you're doing all the hard work anyways, but,,,,, What is the real problem here? So it will need tore down again in the real near future. No motor is made to leak water in the cylinder, this does not just happen!!!! There is (not was) a problem?????
Normally you are not this lucky when you try to do a top end rebuild. Without looking at the head and valve train this is should not be called a top end rebuilt. This is just changing the rings and ignoring the rest
you seem to have all the equipment and engines how about building a 6 pot honda engine allen millyard has all the info on youtube
What was the torque specs?
I really have to complement your skill at methodically explaining each procedure as you moved along during the whole top end rebuilding process. You have a real gift for teaching and making things crystal clear from start to finish! This video is definitely valuable content. Subscribed! Keep them coming’
Wow, thank you!
@@ClassicOctane I agree, really well done, and even though mine is a Kawasaki all the same principles apply. Just one thing, would you recommend engine-in or engine-out? I was originally thinking engine-in but after watching this I might be investing in an engine stand. Cheers.
I have 3 CB750's and a CB550, all of which I would consider yard bikes with extensive exposure and neglect, but, I am hopeful I can get one or two of them running. You have the most comprehensive classic bike repair channel I have ever seen on UA-cam, thank you for publishing these videos. BTW, where is the vid of this engine running?
I'm in the midst of a top end rebuild on my bike. This vid gives me hope. lol.
When removing Piston Rings you should place small rags around the 4 Con Rods so any mishap and you dont end up with foreign objects drop into the bottom of the motor..
Not only that but connecting rods can be damaged if they come in contact with crankcase resulting in stress riser crack and rod to fail in service
You stole my comment. When he snapped ring a piece could have dropped into engine.
I wish I had this video to watch 30 years ago! Nicely done.
The reason the head gasket goes on dry is because any sealer used could possibly block the tiny high pressure oil way holes in the cylinder head and that would be very bad news indeed. One thing I noticed is that the head gasket was not laid flat over the oil rings and you just pushed/dropped the head gently into place and kinda hoped that nothing gets pinched. Hope it works out and no oil leaks.