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Discussion Starter · #1 · (Edited)
Hi guys,

Things I've now noticed on my 72 cb450 that am unsure if related to my recent adjustments or not:

- Black smoke is now coming out of the crank breather when bike has been running for a while (more smoke with throttle open)
- Did spit a bit of oil from crank breather after a ride (visible splash on battery)
- Sometimes some white/grey smoke comes out of right exhaust
- Idle climbs from 1.2k to 1.8k when bike is VERY hot

I recently adjusted the valves a little looser than spec (as recommended on this forum) and patched it back up.

Pressure from exhaust seems strong on both sides (hand check). Rings were replaced + bores honed about 4k KMs ago so would be sad to hear i've blown I ring...

Appreciate any help - am still a novice wrencher.

Thanks,
RC
 

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I'd start with a compression test, after verifying the oil level is correct when measured with the bike held upright. If the oil level is high, and it wasn't before, smell it for fuel.
 

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I have never heard of or seen black smoke from an engine breather. Black smoke in my experience is related to rich mixture. I have only seen black smoke from oil with open flame. Are you sure it is black ?
 
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Discussion Starter · #4 · (Edited)
It's not thick black but it's definitely not white smoke...


I just bought a cheap compression tester and got 75 on right and 70 on left... Surely that's a leaky tester as opposed to real compression, right? Can the bike even run on that little compression? (it came with a long hose and wouldnt screw all the way in)

I've checked oil level on centre stand and it's within the 2 lines on dipstick (don't think the oil smells like gas but the smoke definitely smells bad). I'm using 20w50 as it's been quite warm these last few months (https://www.repco.com.au/en/oils-fl...e-mc-4-st-20w-50-motorcycle-oil-4l/p/A9514996) as manual suggests.

I rode it to get the compression kit and it still pulls pretty well when I open the throttle so im confused at the moment...
 

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Black smoke.... I think soot.
The bad news is that the only way you get smokey breath from the engine is gas blowing past the rings. If you think you are doing the compression test correctly and still getting a low reading try squirting a little engine oil down the plug, if that brings up the pressure then I am afraid it is rings. Brace your self for bad news.
 
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It could be worse than rings; it could be a crack in a piston crown. For both sides to have low compression, assuming a proper test, cracks in both, or bad rings on both, would be a possibility.
 

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Discussion Starter · #9 · (Edited)
Hi all,

Appreciate the advice - Here is where I'm at now:

Did another compression test trying to screw the piece in as best I could (still couldnt get it all the way down...) once bike had been properly warmed up and with throttle fully open.

Results were:
- 95 left
- 90 right

I put a bit of oil in and got:
- 105 left
- 110 right

Definitely think there was some compression leakage but probably not enough to push it into spec. Guess 450roo is right, bad news, blown rings? Pretty devastated...

Would you recommend outsourcing this to a mechanic? I'm not overly proficient on the tools and from what I've read this particular repair can make or break the engine... How long does this type of repair usually need (am trying to quote in my head how much it'd cost at $100p/h + parts)? Or is this something that can be done solo? (Think I'd need specialty tools too right?)

Is it dangerous to ride as is (can I ride it to a mechanics for example)?

Thanks again for the help from a very sad 450 rider...
 

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Riding won't cause more damage in the short run but don't ignore it.
Taking the engine to a mechanic is the safest if you don't know what you are doing. The catch is ... how much money do you have?
Before you take it to a mechanic get in touch with the Vintage Japanese Motorcycle Club or other vintage bike club in your area and find out who is experienced, competent and HONEST working on vintage bikes. Also someone who will search for parts at a good price, buying from your local Honda Dealer can (but not always) be more expensive.
Unfortunately there are sharks out there.
Contact me if you need. Allan <[email protected]>
 
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Discussion Starter · #11 ·
Thanks 450roo.

Have asked VJMC and they can't recommend but have put a note up on their forums on my behalf which is kind of them.

Well regardless of money, I'm going to make the repair. It needs to be done because bike is semi-worthless with those blown rings. In your experience are we talking 1000s? If you think I could get stung on the parts, is it a done thing to buy the parts and provide them to the mechanic so they only look after labour?

Also, I'm not entirely turned off the idea of doing it on my own. I saw Common Motor has just released the final of their videos which covers a ring change... Is it something that can be done with a video/manual walkthrough?
 

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Discussion Starter · #12 ·
I decided to at least take out the engine and break it open as the whole point of getting a vintage bike is to learn to tinker... Here's the problem piston i found. Unsure just yet if there are other issues but as you can see, the rings must have gotten stuck and then started eating into the piston.

Looking at this, do you think it would have scraped the side of the cylinder or is it too hard metal for that? Might go see a machinist to verify...

IMG_1306.jpg

Also when opening I saw the cam chain tensioner had chips in the wheel. Does this look normal/usable?

IMG_1305.jpg
IMG_1304.jpg
 

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I say the cylinder will need bored and oversized pistons. Pour solvent or kerosene in the valve ports and see if they leak. Probably replace that roller if you can find one.

Sent from my SM-J320V using Tapatalk
 

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The tensioner roller is brittle and losing pieces of rubber so yes, as stated above, you should replace it. Honda doesn't sell the roller (or didn't), the whole assembly is intended to be replaced, and good used ones are very hard to find... while NOS versions are even more expensive. If you can find a fairly low mileage used engine (say, from a wreck long ago) you might get lucky, as I did. As these things age, it's nice to have a spare engine or two around for the good used parts
 

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Discussion Starter · #15 ·
The tensioner roller is brittle and losing pieces of rubber so yes, as stated above, you should replace it. Honda doesn't sell the roller (or didn't), the whole assembly is intended to be replaced, and good used ones are very hard to find... while NOS versions are even more expensive. If you can find a fairly low mileage used engine (say, from a wreck long ago) you might get lucky, as I did. As these things age, it's nice to have a spare engine or two around for the good used parts
Thanks ancientdad - Something like this?

https://www.ebay.com/itm/1973-Honda-CB450-CB-450-K6-Cam-Chain-Tensioner/143225089120?hash=item2158e16c60:g:ikwAAOSwf2pcllzY
 

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Yeah, though I'd ask the seller for a few more closeups of the roller itself to get a better view of whether or not the roller looks baked - the only view you have is not a bad one, but it could stand to be closer. Still, at that price it would be a cheap investment
 
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