Topic: CB350F: two failed top end rebuilds, stock bore and 393cc

[Ridem32]

I'm not even sure with a leak down test or compression tester if anything would show up. With the compression rings being new it can still show and hold compression even with a broken oil ring.  But I would run both test just to see the results. I did look at the factory rings and it does show one ring for oil ring. Aftermarket rings use the 3 oil rings like most all oil rings use.  Even if it's a broken oil ring it's not the end of the world it can be replaced.  I think the oil ring on #4 broke after you rode it.  I don't think it's nothing that you did wrong putting it together or breaking it in while riding it.  Run test and let us know.


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[markreimer]

Ok, some more info to share.

I haven't been able to source a leak down tester yet, but I'll just make one if I can't find or borrow something this week. I was able to do a compression test though.

1-2-3-4





Man. Can't get much more consistent than that. All four within 1 psi of each other.

Last year before the rebuild my results were
1: 125
2: 105. 115 max after a few more hits. 180 wet
3: 120
4: 125

Kinda weird that the numbers are actually a touch lower. But they're much more consistent.

 I also pulled the plugs after my 110km ride home on the highway.



It looks to me like 1 is lean, 2/3 are close, and of course 4 is fouled. I've also been getting some black smoke on top of blue. Perhaps 4 is getting way to much fuel from a stuck float or something.

I'm going to pull the carbs so I can look into the head at the valve guides, see if there is any sign of oil running past. While I'm there I'll check the float heights and jets.

Not really any closer to diagnosing the problem. Hopefully a leak down test sheds more light before i have to open it up


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[markreimer]

Here's a photo looking inside the intake of #4. Hard to say if it looks normal or not. Thoughts?





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[markreimer]

Compared to 1/2/3






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[markreimer]

Pulled the carbs, they are immaculate. No dirt or blockages anywhere. Floats were all at exactly 22mm. Quickly ticking off the 'easy' checks before the head comes off.




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[Ridem32]

I sure wish you the best of luck. But I still say broken oil ring on #4.  I hope I'm wrong


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[markreimer]

Managed to make a leak down tester (without a dual gauge) with stuff I had laying around.

I couldn't detect air leaking anywhere even at 80psi. If I increase pressure the engine would turn over. Without second hands that's the best I could do.

So good compression, no obvious leaks. Nothing left to do here but pull the head and check for a blown gasket by the oil seal, and possibly broken rings.

Either way I need new gaskets so I'll order those up now


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[Ridem32]

Keep us informed.  Everything will work out. The worst part of any job is dreading it. Just take your time and do it.  It's really not that bad to pull head and jugs


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[markreimer]

Will do. I know it's a fairly easy affair to pull it apart on a 350F, more-so a pain given the time off the road and the cash. But it must be done.

What do you guys think about how that intake valve guide looks: it appears to me that there is a very light spray of oil in there. But there was no oil pooled on the top of the valve or evidence of oil running down out of the guide that I could see. I'm thinking given how oily that cylinder is, it probably got a bit oily in there when the intake valve opened up. Does that make sense, given that air would be rushing into the cylinder at that moment?



Currently trying to source an OEM gasket set. It was really hard to find some the first time I rebuilt the top end. I might have to go aftermarket 

I hear nothing but bad things about NE gaskets. Versah doesn't appear to have made a 350F kit. Any luck with Athena gaskets on this engine?

[Ridem32]

Check with David silver spares.com


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[markreimer]

I did, no luck. There are three on eBay now. Two come in complete gasket kits for around $250 Canadian (I'm Canadian). That's what I originally bought last year, but it was only around $100 then...

There is one head gasket on its own for $80 Canadian, which I'll probably jump on. That's the most important item. The four oil seals I can order from Honda directly. The base gasket and valve cover o-ring style gasket are available for pretty cheap. I might just have to cobble this all together.

There is also a copper head gasket on eBay. Curious about that. I like the whole resuable aspect, but I know nothing of this seller/manufacturer...

http://www.ebay.ca/itm/161756230924?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

On second though, this says 52mm gasket. 350F pistons are only 47 or so. I wonder if this is meant for a 400F and is mislabelled.

[cphill02]

Any update on what the root cause was?

[RAFster122s]

Copper head gaskets will leak oil, typically only used by race bikes or those who do not mind cleaning oil off the motor regularly.  I would steer clear of a copper head gasket unless you are racing and tearing down the motor often.

[markreimer]

Brought the bike back into the garage finally. Job changes and life etc prevented me from getting back into this motor. Now I've got some time free. I'll report back Thursday night, that's when I'm cracking it open again

[RAFster122s]

Mark,  I think you may misunderstand what a leakdown tester is...or is not.  A leakdown tester is looking to see if a pressurized cylinder leaks "down" from an initial pressurized setting.  It is not a continuously fed cylinder by a compressor to maintain a certain pressure.
You pressurize a cylinder to 80-100-120 psi , then you remove the pressure source.  The gauge holds that pressure and the gauge show you the current pressure in that cylinder...this is done at TDC on compression stroke.  Then you will compare the pressure after a 3-5 minute or longer interval.  You do this test and compare it to other cylinders.  Typically it has a shot of oil in the cylinders to give it a better reading/chance to show a more real life reading.

If you are not able to hold pressure in a cylinder without significant leaking then you have a valve or ring or headgasket issue.

Comparing other cylinders gives you a basis to judge overall engine health and comparatively between cylinders.

Ensuring your valves are properly set is a good idea before this or wet and dry compression checks.

Managed to make a leak down tester (without a dual gauge) with stuff I had laying around.

I couldn't detect air leaking anywhere even at 80psi. If I increase pressure the engine would turn over. Without second hands that's the best I could do.

So good compression, no obvious leaks. Nothing left to do here but pull the head and check for a blown gasket by the oil seal, and possibly broken rings.

Either way I need new gaskets so I'll order those up now


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[markreimer]

I see. I didn't hold it there for 5 minutes, rather I pressurized the cylinder, and listed for air escaping either through the exhaust valve, intake valve, or into the engine case (past the rings). I couldn't hear air hissing anywhere. I had just had new valve seats cut and lapped, with a cylinder hone and new rings, so I didn't expect to hear anything.

Either way, top end comes apart Thursday and it'll be clear as day if I have a broken ring or blown gasket.

[markreimer]

Well I got the engine apart and found some very weird surprises.

First surprise - there were no broken piston rings and no sign of a blown head gasket. Hmm, interesting...


Second surprise. Those OEM oil orifice seals appeared to have disintegrated. It's not clear if that happened during disassembly, but the rubber was pooched. These came in a NOS Honda OEM gasket kit. I had a light layer of hondabond around the seals, and Copper Coat on the head gasket. I'm not sure if they fell apart from age, heat, reaction to the copper, who knows. Maybe I sprayed brake cleaner down there or something and don't remember. Either way, they were fried, but there was no sign of oil leaking past the head gasket.



Third surprise - All four of the pistons tops and valve faces seemed equally sooty and nasty, after only about 100 miles. Though plugs 2/3/4 weren't the worst compared the #1



Fourth surprise, and this is the BIG one. I went to check that I put the rings in #1 in correctly, as that is the cylinder that seemed to burn a boat load of oil. I couldn't find the "top" marking, though I could on the other 3, so I decided to remove the ring for a close look. It does seem that I had it in correctly, but I decided to check the ring end gap. My service manual says the range is 0.1 - 0.3mm, with an absolute max of 0.7. I was somewhere around three times that!! I had a .5, .55 and .6 stacked together and it still fit. WTF.



I never filed these rings. They are NOS OEM Honda. What is weird is that I remember clearly measuring the ring gap and have in my notes that they were close, but still under the max range. So what on earth happened... Maybe I measured it wrong. Or is there some possible way they could have worn that badly so fast? I wouldn't think so...

So I removed a ring from #4 to compare. It was better, but still measured at 0.7, the max limit.

Cylinders look good. Pistons feel snug in the bore.

What next? I'm thinking I could spring for new rings, but what if they are just as loose? Then I'm out $100 for rings. Maybe I just buy the Cruizin Image 393 and bore out the block, then I know everything is good.

Thoughts??




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[Keith]

It is possible that the valve guide seal popped off the guide, vacuum will draw oil through the guide. Leak down won't find that.

[markreimer]

I had my machine shop measure the bore and pistons before they did the hone. They told me there was enough meat there to stay within the piston-to-bore spec in my manual, though 'just' enough. I measured it myself as well and my measurements agreed with them. The piston feels quite tight in there. I'll check again with a micrometer, but I can't imagine it's expanded that much. I mean, I have in my notes that the ring gap was within spec, which is .1-.3mm, wear limit of .7mm. #1 cylinder is around 1.5mm now. That's a huge amount of cylinder to wear away! I can still see the hone cross hatching, and like I said, piston feels very snug and good in there. I had no rattling piston sounds while it ran, and the pistons look good.

Would very large ring gaps alone explain my oil consumption problem, even if the piston to bore clearance is within spec?

[markreimer]

Hi Keith - I checked the seals, they're all where they're supposed to be. See my big post just before this one, I found massive ring gaps on all my cylinders. No broken rings or missing valve seals. My oil supply seals were in bad shape, but no sign of oil creeping past the head gasket anywhere.

[innovativems]

I had my machine shop measure the bore and pistons before they did the hone. They told me there was enough meat there to stay within the piston-to-bore spec in my manual, though 'just' enough. I measured it myself as well and my measurements agreed with them. The piston feels quite tight in there. I'll check again with a micrometer, but I can't imagine it's expanded that much. I mean, I have in my notes that the ring gap was within spec, which is .1-.3mm, wear limit of .7mm. #1 cylinder is around 1.5mm now. That's a huge amount of cylinder to wear away! I can still see the hone cross hatching, and like I said, piston feels very snug and good in there. I had no rattling piston sounds while it ran, and the pistons look good.

Would very large ring gaps alone explain my oil consumption problem, even if the piston to bore clearance is within spec?

Absolutely on a larger ring gap


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[markreimer]

Called my machinist and asked if he can handle a block as small as the 350F. No problem to bore it to 50mm for the Cruizin Image 393cc kit. $190 Canadian for bore/hone. Plus 150 for the kid, and then some gaskets. I think that's what I'll do.

I'm still trying to figure out how that one ring had such a huge gap. Every time I've used Honda rings they haven't needed filing. It doesn't appear that the cylinder was worn at all (it shouldn't have been..) and the ring looks normal. What do you guys think - bad ring that I forgot to measure? Or is there some way a ring could actually wear that much, that quickly?

[innovativems]

With doing the big bore I would add a ttr400 oil cooler setup as it makes the cylinder sleeves pretty thin. 

I would guess the ring was off when out in


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[markreimer]

Cool, I'll look into it.

Ordered the 393 kit, should be here in 1-2 weeks. Then my machinist needs a week to do the overbore, so I'd guess end of the month it should be back together. This is my wife's bike mostly, so she just puts around the city. I'm not too worried about the heat there. But when I ride it that's a different story 

[markreimer]

Hah fair point. It's usually under 77F while riding here, other than a few weekends of the year. Spends more time riding in mid 60's honestly.

So the big bore kit will solve a few of my issues here - the ring gap, piston to bore clearance, etc.

But I still have other issues. Namely, why did those critical oil orifice seals deteriorate so badly. They were OEM Honda. Anyone have an idea? All the other seals from that kit were in new condition still. I coated them in Hondabond, but that shouldn't have hurt it. Copper Coat shouldn't have either.

I wondered if maybe they were crushed and ripped during installation. The head was decked slightly, the block was not. Perhaps it was over compressed as a result? Hmm...

The Cruizin Image kit comes with a head gasket for the 50mm pistons, but I'll still need a base gasket, valve cover o-ring gasket, exhaust gaskets and the oil line seals... I'm thinking I'll order new OEM oil orifice seals if I can find them, but I'd rather not buy them as part of some 40 year old kit again.

The base gasket and valve cover can be whatever brand, NE or something, those are usually pretty easy to keep leak-free.