How-To: Honda CB500 CB550 CB650 Top End Rebuild
Does you CB have a leaky head gasket? How about low compression? Chances are it has both problems mentioned. I have found that both issues are very common problems on these models. In this 6hr 30min long video, I will walk you through the rebuild process step by step to eliminate leaks and restore compression.
Year, Make, Model
This video covers all 1971-1973 CB500F & 1974-1978 CB550F models. Also covers CB650 1979-1982 models.
Head Gasket Oil Leak
A common leak found on these models is the oil passage on the end of the cylinder banks which supply oil to the top of the motor. There are o-rings located between head and cylinder that typically get dry and brittle over time, eventually causing a leak. At a minimum, the head gasket needs to be replaced. However, I would recommend that the cylinder base gasket be replaced as well. When the head is removed, the clamping pressure is released from the base gasket, and you may get a leak once it is all put together. Also, with the cylinder removed, you can inspect the cam tensioner which is known to develop cracks, so this will give you the opportunity to inspect that as well.
Compression & Leak Down Test
It’s also a good idea to perform a compression test on any motor that has been sitting for a while or you are about to tear apart. Why? So you can address any issues while apart.
First up is the compression test. Here is the gauge I use that comes with a 12mm adapter required for this motor. Results for cold and dry are listed below. Adding some oil to #2 cylinder did not change the readings all that much, which indicates that the piston rings are sealing properly.
#1 before rebuild – 117psi
#2 before rebuild – 97psi
#3 before rebuild – 140psi
#4 before rebuild – 140psi
Hmmmm, something is up with all the cylinders, especially #1 & #2 considering the manual calls for ~156-170psi. Now what? Well, we found a problem, however do not know what is causing the low compression results. At this point a leak down test needs to be performed to find the source of the leak. Check out my DIY leak down tester build here. Leak down test results:
#1 before rebuild – leaking exhaust valve
#2 before rebuild – 27-37% leaking exhaust valve
#3 before rebuild – leaking exhaust valve
#4 before rebuild – leaking exhaust valve
Keep in mind an engine in excellent health will have leakage up to 5%, while up to 15-20% leakage is considered normal before a rebuild is necessary. Now 37% on #2 is clearly a problem! At this point we are all probably thinking it is time for a valve job. However, in the video I demonstrate that a couple of light taps on the valve stem with a piece of wood decreases the leakage. This means that I am knocking carbon off that is preventing proper sealing.
After rebuild leak down results on #2 cylinder falls right at 4.5%….perfect! And compression is back to 150-170psi on each cylinder per manual specs!
Leak Down Formula
I want to explain the formula on how to calculate leakage. Using 100psi works great for easy math, however in some cases that much pressure will roll the motor over. In this video, I happen to use 22psi of supply air pressure, and at one point in the video, the gauge read 16psi measured air pressure. So using the formula below, ((22-16)/22) X 100% = 27% leakage.
Tools
Here is a list of tools used in this video. I bought most of the stuff from Amazon.
Actron CP7828 Professional Compression Tester
Motion Pro valve core remover tool
Vessel Impacta P3 JIS screwdriver
Vessel impacta P2 JIS screwdriver
Lisle valve suction cup tool for lapping
Permatex valve lapping compound
Parts
The full gasket set does not come with everything you need. I ordered the copper/AL washers and rubber “pucks” under the valve cover from my local Honda dealer.
Before And After Pictures
Here are some before/after pictures of various parts. The valves were cleaned up with a wire wheel while the rest of the components were soda blasted, which works great for removing carbon and gasket material. The cylinders were also hit with a ball hone to remove any glazing and give it a nice crosshatch finish.
Other Helpful Videos
Here is a video that explains how to build a leak down tester.
Can you replace the head gasket on the CB500 four with the motor still mounted in the frame? I don’t want to remove the motor if I don’t have to. Thank you for sharing your experience and knowledge.
Hello Matthew. I lost my cb500Four service manual.. I bought from you last summer.. now I need it again.. can you send me that service manual again to me?
Go ahead and access the video again, the service manual is in the library.
Hey great vids. I am doing the top end on a 1975 cb550k and i noticed that your how to video was for a 550f anyway my question is re installing the cam using the t marker do i need to set the tdc on the #1 compression stroke or just tdc without knowing if its compression or exhaust? Thanks so much for any info Oh and the cam lobes look asymmetrical should they be?
Before timing the cam, just make sure #1 is at top of stroke. Then line up the cam, and install the chain.
Hi, could I used this for 1978 cb750, I realized there are a few differences with measurements etc. But I figure lapping the valves and other general procedure might be helpful. Thanks.
The 750 is really different. I’m actually working on rebuild videos for the 750. Just split the cases.
Here is the project bike: https://youtu.be/gDDRZOioPRc
However, this video does have good info that will help you in the meantime.
Matt
Just finished total bottom end rebuild on 1975 cb550k. Could not have done without your video! I had a couple questions which you answered, Best $30 I ever spent. Top end video rebuild next! Can’t wait to get started! I owe you a beer or six.
Glen,
Thanks for the feedback!
Matt
Thanks for your video it’s very helpful! I just have one question. Where did you get your cam chain tensioner? Mine is cracked up in pretty bad shape.
Thanks,
Ebay. Just search the OEM PN and some hopefully are 4 sale.
After the valves were lapped, all you used to clean lapping compound in the video was a cloth. Is that sufficient to remove all the grit from the heads and the valves?
You can clean with brake clean or solvent if you are worried about it.
Hi, i bought your video, but can’t download it, unfortunately, in my workshop bad internet connection. Are there any ways to download it?
Boris,
It is streaming only, sorry.
Tell me about your workshop location relative to house. I had to add internet and used a powerline adapter. This system sends internet over the electrical lines. Works mint.
I am in Russia, bro(
I am in Russia, bro(
Hi Boris from Russia!
Hi Matthew,
I finally bought the video to tackle fixing my CB550, it makes it easier to watch and replicate, versus looking through the repair manual, so thank you for taking the time to make this video.
I noticed that using cleaning oven like easy off, makes the gasket softer and easier to remove, just spray generously ( wait about 30 minutes} and resist the urge to attack it after 5 minutes :-).
works great on carbon deposit too.
I’ll give that a shot next time, thanks for the tip. I thought oven cleaner will damage aluminum?
no it doesn’t
OK thanks.
don’t leave it overnight though, it will discolor the aluminium.
1/2 hour max.
Will not let me view video after purchasing
I emailed you.
Hello Matthew ,
Just came across your videos. I recently acquired a 1981 Honda CB900c and was wondering if your REBUILD video translates to my motorcycle? If not, do you know of any helpful videos tht would help me through this process? Thnks!
No, this video is not applicable to your model. Not sure if there is a video out there on it or not.
I I purchased your rebuild CB 550 video about a year ago. I accidentally deleted the link to were I can watch it. could you resend it to my email please?
My email is josiahshelton_333@hotmail.com
Nothing coming up at that email. What email did you buy it with?
Hi Matthew
Going to replace the gaskets in my top end to fix the oil leaking out from there, will buy your vid once the parts arrive and it’s time for the job – just wondering, is it worth doing the rings and valve stem seals? Each looks like a bit more work and necessitates buying the extra tools and whatnot. It runs well and I’m only replacing the gaskets to fix the oil weeping from the head, my only concern is that its a higher mileage bike with almost 40k miles on it so dunno if pistons rings and stem seals are something i should address – or is it a “if it aint broke dont fix” kinda thing.
Thanks mate
F
I’d recommend replacing every gasket and valve stem seals since it will be apart. Rings can be evaluated once apart.
Thanks mate. The gasket kit just arrived in sydney so I go the vid but I also so need to order the pucks and washers from my local honda guy. Are these correct? Anything else im missing?
6 x 91318300013 – Sealing rubber “pucks”
12 x 90485035000 – washers
Funny enough the 4into1 NE kit has come with some pucks, but i’ll get OEM. Thanks mate.
I think you have everything you need. Good luck!
On my cb 550 some of the head bolt washers were thicker some were thinner they got mixed up were do they go
Should all be the same. Check the parts diagram, if all the same PN, then someone installed the incorrect ones years ago.
Hey there i did a top engine rebuild and now it wont start no compression at all. Does this video include valve rebuilds and timing? I just want to know if this video can help me. Please cotact me asap thanks a lot man
Yes, it covers all of that.
Hey Matthew,
Bought the video and it’s really helpful! Thanks!
I’ve been reading a lot (probably over-complicating) the different head gaskets and cylinder gaskets available on the market. I originally bought the standard set from 4into1.com, but I’m wondering if you have a recommendation for a full gasket set? I saw you recommend the NE brand one above, but I’ve read about some issues with the head gasket that comes supplied.
Any thoughts?
Thanks in advance!
I haven’t had any issues with the NE brand.
MLS would be a great option as well (scroll all the way down): http://www.cyclexchange.net/500-550-Hi-Perf.htm
Will this video work for a 1975 CB550K? I noticed models listed are the F . Am I correct in assuming the top ends are the same?
Yes, this video will apply.
Matthew,
I purchased the CB 550k top end rebuild video back in December of 2021. I finally have all of my parts and I went to watch the video once again and I am blocked from doing so on my computer. Right clicking on the video and going into properties general selection gives me no option to unblock. Any thoughts about what to do. Thanks,
Please send me an email and I can get tech support involved. A screenshot of the issue would be helpful.
Hi! I have a 1984 Honda CB650, i was wondering if the process is similar? I noticed in your description its up to 1982.
Please advise, thank you
Your engine is a DOHC, totally different.