cb350 piston/cylinder clearance

overdraft

overdraft

Coast to Coast
hey wise people... i bought a set of first over pistons for my cb350 and i'm about to sent the cylinders off to be bored out... is the clearance between cylinder and piston something the machine shop will know about based on the pistons (which i presume i should give to them for reference) or do i have to supply the spec? i've pored over the shop manual but it doesn't seem to tell me... any thoughts? thanks guys...
 
Check stock piston size, check stock bore size, take the small number away from the big number, that's the clearance.
Personally I think 0.003" is too much.
As long as you warm up motor before beating on it, 0.0015"~0.0017" is plenty.
I run my CB380's at that clearance (2mm overbore 360) and my XS'800' (8mm over XS650 ;D )
Very few machine shops deal with motorcycles, those that do will either bore a bit 'slack' to prevent seizing or to the exact size for a low revving car engine with a much larger piston
 
ok, back to the manual to do some arithmetic (duh... i could have done the math if it'd thought of it!) so taking the manual's range for 'standard value' for both:
cylinder 2.5201 - 2.5205"
piston 2.5185 - 2.5193"
so if you put the smallest 'standard' piston in the biggest cylinder you have .002" clearance
and the biggest piston in the smallest cylinder yields .0008" clearance
split the difference at .0014"? bit too tight maybe?
 
Sounds about right to me, aim for one and a half thou and keep it under two thou(0.0015"~0.002")
clearance depends on piston expansion, if timing is right and jetting is good/slightly rich it wont be a problem
I know how ART pistons 'work' so use a clearance that works.
The cast 'stock' pistons just expand less than a forged piston or pistons from a different supplier. (Wiseco need at least double stock clearance because they expand so much more)
 
well shit... i've got aftermarket ones which i got from Sirius Consolidated Inc which are listed simply as 'made in japan' so i'm not sure what the characteristics might be... i gotta say they look more like a wiseco than an oem cast piece...
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so now what?

fwiw, here is Sirius' response to my question, delivered promply i might add...

Normally the machine shop should know this info sir...we have actually never been asked this before and have sold 1000 of these sets?? Try the Honda manual as these were made to OEM specs sir...
Sincerely Martin
 
I had .002 down with NOS Rocky 3MM over pistons. Been running great for the past year.
 
djelliott said:
I had .002 down with NOS Rocky 3MM over pistons. Been running great for the past year.
Click to expand...
thanks for the input! i guess i'm walkin' on the wild side here without knowing what make these pistons are... if they behave like oem and i give 'em extra room they're gonna slap around in there... if i go with the clearance for the oem ones and they swell up like... well, pick a simile... and it ends up seizing... ugh... i guess if they sieze there's always second over!
 
They are cast pistons, use stock clearance.
The only real difference to stock is the crowns are machined
I guess you've never had a Wiseco to look at?
 
O.P., I see it's been two years experience with this piston set. How's that work out for you?

I'm considering buying the exact set. Unbelievable price, but I'm quite worried that it may be too good to be true...
 
they've been fine! I haven't logged a ton of mile and I haven't pulled the head to look at them either, but operationally they've been great. i've revved the hell out of them and bogged around town, the whole thing... I'd buy them again for sure... they're barely more than the price of a set of oem rings and you get pistons, rings, wrist pins and clips!
 
That's what made this set so appealing. 1mm oversize already on their way. Why go from standard to fourth-over? Cut the BS out. CB350's will continue to slap around the cylinders until about the third or fourth, so I'm saving a lot of annoyance in the future...

Now how to I get the machine shop to do the top end without any baths that would remove the beautiful cruddy shmetina....
 
Re: Re: cb350 piston/cylinder clearance

Redliner said:
That's what made this set so appealing. 1mm oversize already on their way. Why go from standard to fourth-over?
Click to expand...

So you can rebore a couple more times before running out of cylinder. At the price though - and no shortage of 350 jugs - sounds like a plan to me.
 
Well when you have five of these bad puppies piled up on eachother just waiting to breathe again...

Besides, I know what I'm doing here. I know to stack the ring gaps and lock-tite the hell out of the plugs. A little bit of lithium grease in the cylinders when reassembling doesn't hurt and of course torque EVERYTHING until you hear a nice steel-on-aluminium squeak like a tiny barn door or the death-groan of a gremlin. Yep, daddy sure did a number on me...
 
Do people not install pistons dry? I do this on my dirtbikes to aid in ring bedding. eg

https://www.google.com.au/search?q=how+to+run+in+motor&ie=UTF-8&oe=UTF-8&hl=en&client=safari
 
Somehow I was afraid that somebody would take my dumbass advice.

Install dry or only with the same motor oil you intend to use. Otherwise they'll slip and line up your ring gaps (no-no) and take longer to seat.

If you use the oil that's going in the engine, it won't be as slippery as some greases, it won't displace engine oil (BIG no-no), and it won't make a difference in seating since your walls are going to get tossed with oil anyhow.

For future reference, don't read anything I post or you'll just be really really confounded and upset.
 
I oil the last half inch of piston skirt but leave rings dry.
Major ring seating is probably first 2 minutes, just put it in gear and hold on the brake as soon as motor is warm (bit nasty on clutch though)
I've even 'loaded' the motor while warming up, only for a few seconds at a time
I also use real cheap oil for initial start up, after engine has gotten up to temp and you've 'loaded' the rings, shut it down and do oil change with whatever your going to run for 500 miles (that's why you use cheapest for initial start, it won't break down in 10 ~ 15 mins)
 
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