Only 25 psi of compression... Let's find out why.

In this video we tear into my CB500 engine to figure out why we only have 25 PSI of compression in one of the cylinders.
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[@RIPPERTON]

First thing I would have checked before removing any parts is check valve clearances. It may have had a tight valve clearance or a stuck valve.

[@andrewf8486]

Can you do another compression test, I’d like to see how much it improved, and how close each cylinder is now.

[@jackrichardson6211]

I've been binge watching all of your videos for nearly two weeks now, I recently aquired a 78 CB750 that is very near and dear to my heart and your videos have been helping me so much during the rebuild and the problems that i have been finding. I'm so happy with how well you have done and that this has turned into a dream job for you bc you are really good at explaining the "Hows and why's" of most of the issues. I would go as far as to say that you are a natural born teacher. Thank you for all the videos and the hard work you put into them with the actual work, the filming and the editing.

[@brianaurora9128]

Random: I was watching one of your videos and heard you say you like Mustie1 and some people negatively say you “copy” him. I watch his channel religiously and I think you do your own thing. Nothing wrong with drawing inspiration though. He’s got really educational content. You’re much more informational in your areas of expertise. Keep doing you. Just wanted to say that.

[@edwardmulder3777]

Engine sounds great, I remember when my '74 550 got new rings the performance was night and day, instant throttle response, loved it.

[@scottb8175]

That is a very clean CB500! I don't see many that nice around here. My favorite of the CB-fours are the 500/550, the 400 a distant third because it has much less power but almost weighs the same. The 500/550 are the best engineered of the SOHC fours by far - head and shoulders above the over - complex CB750...

[@volvogt21]

Very pretty bike. So glad you're keeping it stock.

[@ClassicOctane]

This one was way too nice to cut up.

[@Pnw-nick]

I want to see the new numbers after all the work!

[@ClassicOctane]

I will do another compression test after the rings seat a bit more.

[@kamillapaj87]

Newer heard starter motor spinning so fast in my life :D

[@stevezephyr]

Quick test for the valves, whilst the head is upside down with the plugs in, pour petrol in each chamber and see if it leaks away. But yes I'd agree with your initial assessment that it's a cylinder problem even though all seems okay.

[@ernestlajoie8561]

well done Taylor ! I'm very pleased that you shared this with us and happy we the wonderful sound after building back up. This great sound makes all of us confident that you solved it🙂 Looking forward...

[@maxheadflow]

One thing to note is that the bit you have in the impact wrench is a number 2, you need a number 3 for 6mm screws.

[@noahway13]

I get the feeling there was a real mechanic, just out of sight, coaching him along.

[@MichioMakes]

Heck yeah! Was looking forward to this video.

[@m.e.g.a.n.l.e.i.g.h]

My dad owned a 67 550 and said it was the best bike he ever had. Very dependable for 5 years. (18 k) not much for a 5 years he owned it. But he took care of it beyond the normal maintenance and appearance. The pictures I've seen look like it was new. He misses the Honda 4s of the day. Just to say love of the bike. He did say he'd of loved for you to make a cafe style bike of of it.. thanks for all your videos.

[@rundllx3228]

You always have to check valve clearance first. It was common practice back in the day to correct the clearance because things like loss of compression can stem from wrong valve clearances. Also that could be the reason why it was abandoned in the first place

[@mikegermain7033]

You make the work seem so effortless but I understand you know what your doing and it shows. Great video 👍

[@ClassicOctane]

Thanks, I have done these top end rebuilds a bunch of times so I know exactly what to expect.

[@Bugholeexcalibur]

The engine looks spotless. A real beaut.

[@ClassicOctane]

Thanks!

[@scottminshall6420]

Good job Taylor!

[@GraemeRobinson]

A nice moment to see it run.

[@dadawoodslife]

"JIS screws are crazy easy to strip out", yes, especially if you aren't using an actual JIS bit.

[@SteffanoDucati]

Good video as usual. Think I mentioned this before . A leak down test can save a lot of guess work. I also wonder if you checked to see if whoever had this apart lined up the ring end gaps on the top 2 rings .... I've seen it in my shop more than once ...

[@grayfool]

Sounds very nice. From the intial turning over it sounde very even. Love to know what the pressures are now.

[@MotoMango]

Great work man!!

[@CCitis]

You make it look easy... and it isn't! Cheers.

[@jeremyr62]

I have to get me a bike lift like that. Looks great.

[@junglie]

My mate had a 5004 in the early 80's & I always liked the look of them compared to the 550, then n the late 80's i bought one from a guy at work for a freind , fully restored & needle roller conversion to the cams, it ran great but oh dear, the handling.......like riding a chest of drawers on casters with a engine on top......

[@bookemdanno2737]

BIG THUMBS UP !!,,,Another GREAT video !!

[@ClassicOctane]

Thank you! Cheers!

[@Bassman1999]

Good work!

[@jeanlawson9133]

I like those Honda's... I have had a 350 Four..550 Four.... and 750 Four..... Nice 69 Camaro is it a DZ car... Great video content... thanks for sharing. That cylinder looks different on the head the dark circle around the Piston area near the valves.

[@nicholasbishop3300]

Sounds much stronger and smoother Nick Australia

[@stemocore]

Honda CB500 It's the bike that I've always dreamed of, but I probably won't have a chance to own it.

[@bingosunnoon9341]

Old Japanese bikes? I bought a CB500F brand new, 1500 bucks with a sissy bar thrown in. My favorite girl wouldn't ride without it. Watching this video made me glad that I switched to electric years ago. Ain't never going back to gasoline.

[@blackbuttecruizr]

Great Vid, love the sound track. Wonder if it was a fresh rebuild, maybe they forgot to clock the rings and there was blow by?

[@ClassicOctane]

It's possible

[@swordfish1120]

Sounds nice! Do u perform leak down tests on these bikes to troubleshoot, or do you like the compression test and remove the heads for a visual?

[@tanzerfigueroa1894]

Awesome video ! question when you had the the cylinder off I noticed oil restrictor in block right side, assuming they are the same on both outboard sides? Reason I ask Im working on my 1973 CB500 and the left hand oil restrictor was actually not there just the tube. and my right side restrictor was intact. Reason for tear down was the right side of cam was not really getting oil, but the left side was flooding immediately. I bought the bike like this and found the cam was shot rightr side only. Now wondering is restictor critical for oil supply to upper end? Now I need a head and a oil restrictor to make right. Any recommendation for head and restrictors ? Thank you in advance.

[@plageran]

nice vid, thanks man. should i redo my 250r atleast i won't be to scared to try.....

[@terryfraser7259]

Awesome. Do you think the rebuild work fixed the compression (assuming it’s all ok now) or could it have been a tight clearance holding a valve open. Could you have done a pressure leak down test? Enjoying your channel.

[@mariodesmo]

As you obviously know, when you crank over an engine and you get a steady turn-over speed, that indicates comparable compression in each cylinder. When you hear the engine speed up for one split second while cranking over, then it has a weak cylinder and you get that wah-wah-WAH-wah, wah-wah-WAH-wah, wah-wah-WAH-wah sound, if that makes sense. The engine turned over very smoothly after your rebuilt it so I think it's fine now. Still a mystery as to why it had no compression before??? What about your gauge, could there be something causing it to read off? Leaky gauge/hose, fitting???

[@bingosunnoon9341]

Nothing beats a measurement.

[@richardvandervoort]

And now a set of decent exhaust pipes would be nice.

[@kurtyoung6769]

I stopped to check the ring gap spec. for the cb 500. My intuition was correct. .......5 thousanths to 13 thousanths is the range for both compression rings. See my comment 8 minutes ago.

[@toine0002]

love it

[@hlpang1075]

No compression test after? I am guessing maybe the mating surfaces could be off, or bolts maybe not torqued down enough causing a leak past the gasket. But then there would have been an oil weep / leak…

[@danthemowermedic4444]

Got a link to a JIS bit that fits into the impact driver? I have been searching and cant find one!!!

[@BrickHouseBuilds]

amzn.to/3O5deb3

[@90blacknight]

You cannot work on an old Japanese bike without a manual impact driver! Do yourself a big favour and replace all those JIS screws, which are made of cheese, with allen bolts/screws.

[@starsailor49]

Yep, original Japanese fasteners always disintegrate.

[@marcinhanderek4247]

Hi ,how good presure in this bike hondacb500 k3 ?

[@daveco1270]

Did you paint the engine on that bike? It looks really clean. It's nice that you can access the top end with the engine in the frame. That's the only thing I don't like about my CB750...apparently it's not possible to do any top end work without pulling the engine out of the frame.

[@gummitarzan8545]

dohc?

[@daveco1270]

@@gummitarzan8545 No, SOHC 1975 CB750.

[@ClassicOctane]

I did paint it when I originally put it in. I find the 500/550 bikes are much nicer to work on.

[@gregstotts1638]

How good/bad are the '81 CB650 Customs? Thanks

[@ducaduke]

Words of wisdom from a old machinist only file down one side. So you only have to deburr one side not both !

[@kurtyoung6769]

I stopped at 11:00 to suggest that .02 for the 2nd ring gap sounds like the maximum not the minimum measurement. The measured gap being .014 sounds like the minimum gap. Of course this is my opinion but I've done my share of engine work.

[@SuperTambo69]

Maybe those old rings lost a bit of tension. What did they look like regards wear? If past builder didnt do end gaps, maybe he put them upside down? Gaps unclocked? Anyway, good outcome

[@ClassicOctane]

They forgot a few things so I wouldn't be surprised if they were in upside down. I didn't check.

[@cozydram1]

neat

[@fishaussie9112]

Great to see you back wrenching on old Honda’s Better then all the other car crap

[@olliem199]

Did you do a leakdown test?

[@SB-vb8ch]

Thinking exactly the same. Leakdown tester & a keen ear would have highlighted an issue with valve seating etc.

[@Mo_G]

👍👍👍

[@dangeranger69]

did you put oil down the cylinder before the test?

[@ClassicOctane]

Tested dry and got 25 PSI. Put oil in and it jumped to 100.

[@dangeranger69]

@@ClassicOctane 100dosnt seem low the rings need oil to seal properly, but atleast you know whats going on inside now so you dont have to worry

[@handyhippie6548]

since you didn't find an issue, it makes a person wonder what was up in the first place. 100psi difference in compression in one cylinder is concerning, and finding nothing wrong after teardown is just wrong. must have been a stuck ring that popped loose as you worked on it like you said. i would be somewhat miffed if it were me. that's a lot of time and effort spent without an aha moment. but you know now you have a good engine and you got to do a refresh job on it, so that's something.

[@ClassicOctane]

I really expected to see something very obviously wrong with those numbers. I guess it will remain a mystery. The gaskets and o-rings were dry and leaking anyway so it was worth doing.

[@adamlannerd1408]

Motorcycles!

[@daveco1270]

What's the working theory on why the compression was so low before you took it apart? It doesn't seem like there was an obvious culprit.

[@ClassicOctane]

My guess was stuck piston rings that freed up before I got it apart.

[@mickducati1947]

😜🏍👍

[@hendrikdegraeve7554]

How's the compression now?!

[@ClassicOctane]

I will test it again once the rings are seated a little more.

[@hendrikdegraeve7554]

@@ClassicOctane So not sure if I missed it but, have you tested them again recently?

[@chuckymurlo5654]

I take possession of a barn find 74 CB350 Four next week and it looks to me most procedures used on a 500 or 550 could apply to the little brother. Never used a cylinder hone before but I certainly know the concept. Seating brake pads to new rotors for example. With the puny cylinder bores maybe I could use a wheel brake cylinder hone. lol

[@rickmoranis392]

Could your cam have previously been out of time, causing the low compression? I’ve had that happen before where someone swapped the intake and exhaust cams (DOHC in my case). Fortunately, it wasn’t an interference engine.

[@ClassicOctane]

I would think that would cause low numbers across all 4 but to be honest i'm not sure. It's possible.

[@harleyhem3381]

Something isn't adding up here. I'm just hoping ur feeler gauge is in thousands of an ince and not in mm's.

[@toddanderson7942]

You knew you had low compression and didn’t take the precautions of putting cloth rags in the crank case around the connecting rods to catch potential broken piston rings before you slid the cylinder barrel up over the pistons. You lucked out.

[@hendrikdegraeve7554]

Also how come you get these 500's, 550's, 750's like its nothing... Back in europe bikes in terrible condition will cost you 2500 eur's and they are usually really bad condition. For a decent one, its probably 5500 to 7000 eur here... I'm looking for one to completely rebuild but everyone is asking crazy prices.

[@CCitis]

Same in Canada... first, you can' t find them. Second, they are expensive. Even non running ones. I bought a 71 CL450 last year, and it was not cheap... and it needed lots of work. Still trying to get it running right.

[@owen368]

You mention what I have noticed that they seem to have a fair old number of cbs in not bad condition, as you say anything that old in UK is not cheap and in poor condition partly thanks to our rubbish weather.

[@worsttintentions]

Did you figure out the root cause? Seems like a tight ring gap wouldn’t be it. We’re the previous ones the wrong depth?

[@90blacknight]

Guessing it was valves.

[@ClassicOctane]

Never found the exact cause but it seems to be sorted now.

[@damianbrennan2258]

Valve adjustment or valves 🙄

[@danaowen9014]

Im thinking that mabe the head was not torqued evenly and allowed the compression to leak past the head gasket.

[@ClassicOctane]

I inspected the gasket for any evidence of that but didn't see anything.

[@robstuckey]

compression improvement after adding oil = pistons are crap cmon bruh

[@towerdave4836]

So why didn’t you check the compression before completing the reassembly?

[@Jaysqualityparts]

Vacuum leak

[@treycurrieba]

fIrST. 🥳

[@dippyism]

Get rid of the crap music

[@BrickHouseBuilds]

Your musical tastes are just bad dont worry

[@owen368]

2nded