Topic: cb350 issues

[Gittfiddler]

Hey Folks,
I had a 72' cb350 that a "buddy" missed a gear and broke off a valve for me.  I had the head rebuilt with new valve seats, put new valves all around, standard pistons & rings, cam chain tensioner.  Got it back together and running and didn't do any fine tuning because I wasn't riding it.  Well, I had to trade it for some work I had had done and I disclosed to the new owner that it had to be tuned up before he could ride it any distance and that it had to be broken-in properly.  So what does he do but immediately takes it for a cruse and it over heats and stalls out.  I took it back and did the final tweeking myself and had it running great, more power, long rides no overheating.  He takes it back and has the same issue.  He is now in a different city and I told him that he has a vintage bike and that if he wasn't willing to work on it himself he'd better find a good mechanic who can.  He took it to a guy who checked it out and did a compression test and found the left cylinder has 130 lbs compression and the right is at 80 lbs.  He also said that the cylinder walls were ground too coarse and that would cause the rings to wear prematurely.  I did run a hone through the jugs, very sparingly with fluid to knock down ridges.  I did lap the valves, and followed the clymer manual on installing the rings.  The bike only had 8k original miles so I didn't think it necessary to bore oversize. 
My questions are,
Has anyone experienced the overheating issue?
Are the out-of-the-box cylinder hone stones too coarse for honda rings?
Is this mechanic trying to scare this guy because he doesn't want the job?

I know there are a lot of open ends to my situations but any advice would be appreciated.

[Nikkisixx]

Are the out-of-the-box cylinder hone stones too coarse for honda rings?

Hey gitfidler, it sucks you are working on a bike you sold but it is mighty nice of you to do so!  Not many people would do that, "caveate emptor" as it were. 

I hate to answer a question with a question but when you say you honed it, you used a hone and not a dingleberry?  Is it possible you took a little too much out and the rings aren't sealing?  Stones come in different grit, can vary from manufacture, and can be fairly aggressive.  Did you mic the bores after you honed them?  Unless the mechanic has the head off and is looking at the cylinder he is just guessing at this point. 

[Gittfiddler]

By dingleberry do you mean like the bottle brush with abrasive balls at the ends?  No, I used a 3-stone spring loaded deal in a cordless drill.  My goal was to even out the ridges at the top and scuff the wall surface glaze.  I really might have done 10-20 sec per sleeve, trying not to remove hardly any material.  From past experience and all the info I have read, my thinking was that a slightly scuffed cylinder wall is what you want for the rings and the sleeve to wear into each other.

I haven't done a search yet, but would a leak-down test help find where the issue is coming from?  Never seen one done either.

[Nikkisixx]

From past experience and all the info I have read, my thinking was that a slightly scuffed cylinder wall is what you want for the rings and the sleeve to wear into each other.

Yup, your thinking is sound.  The ridge you mention can be carbon buildup or it can indicate the amount of wear.  It can also hold the hone stones cockeyed in the bore which leads to an uneven cylinder wall.  With so few miles, I'd guess it was mostly carbon.  With such a light hone, your walls are probably fine. 

I haven't done a search yet, but would a leak-down test help find where the issue is coming from?  Never seen one done either.

A leak down test would indicate where the compression is sneaking away.  If you have the tools (compressor and gauge) and knowledge it would be helpful in your situation.  A lot of auto part stores will loan or rent the gauge you need.  This here interweb has all the info you need to perform the test. 

Now, I don't know this mechanic from Adam's housecat, but  you should go behind him and check the compression and what not yourself if you can.

[kirkn]

Wait, what?? 

I'm missing something here - you sold (traded) the bike, and you clearly said work was required.  He took it anyway, then brought it back, you fixed it up great (to your own satisfaction), then he takes it away again and has MORE problems?  Any he's moved away to another city???

Why is this even a problem anymore?  I'm thinking "hey, it was running perfect when it left here last...."

Just my two cents...

[Nikkisixx]

I'm missing something here - you sold (traded) the bike, and you clearly said work was required.  He took it anyway, then brought it back, you fixed it up great (to your own satisfaction), then he takes it away again and has MORE problems?  Any he's moved away to another city???

Why is this even a problem anymore?  I'm thinking "hey, it was running perfect when it left here last...."

Just my two cents...

Yup, hella nice guy to go through any issues.  Gittfidler, will you sell me a 30 year old bike and provide a warranty? 

[Gittfiddler]

Luckily, he's not insisting I deal with the problem.  I just want to be able to give reasonable advice on what he should do with it.  It was a fun, clean bike when I let a friend ride it and blow it up for me. now it's a pain in the ass and bums me out that it's gone to someone who wanted to look like a hipster and can't keep it going.

Does anyone think that if the bike was ridden gingerly and broken in well it might get better? It only has about 25 miles on it since the topend build.

[Nikkisixx]

If you want to see if it will heal itself, it should be given a fighting chance.  Fix whatever is making it overheat (lean-out?), give it some fresh oil, make sure the valves are adjusted, you know - basic tune up stuff.  Then baby it for a while - no high revs and stay close to home.  Tell your hipster buddy (there are hipsters in Idaho?) to take it easy on it for the first 500 miles and you may be ok.  Good luck man!

[low-side]

     It sounds like this guy has already fried it - literally.  It sounds like his mechanic is trying to make him feel better with the cylinder wall finish crap.  With the rings these bikes used it would be pretty hard to produce too rough a finish for them if the bore were bored and honed or even just honed with a glaze breaker.  What sounds much more likely is that one cylinder was slightly tighter than the other and this guy took it out and beat it so badly that it over heated and cooked the rings on one side and they don't have any tension anymore.  I've seen that happen before, and this sounds right for it.  Or it might be completely off   Whatever it turns out to be, good luck to you both.