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Discussion Starter #1
Alright, I need some help forming a rebuild strategy for my CB160 racer.

I've got a junkyard motor and it's all torn down. I found a decent crank assembly (the bearings on the original were huffed from sitting for years with water in the cases). The head looks clean, and it doesn't appear the motor was neglected or abused when it last ran.

The pistons have a ".5" stamped on them, so I'm assuming they've been bored over. I was just going to give the cylinders a light honing, re-ring the pistons and call it done. However, the right cylinder has some dark stains on the wall that after some honing do not go away. I can't see or feel any gouges.

My strategy questions;

1. I've got .5 rings and can go with the original plan.

2. I've also got an s3 overbore kit w/ head gasket that I could go with after having the cylinders bored over (time + money)

3. Can someone explain to me the differnt overbore dimensions and nomenclature? How much over is an s3 kit? Is a .5 kit .5mm over?


I should also add that my main objective is to just get out on the track, there's time enough for building a Branson Super Sloper later on.



Honda go sideways!

Edited by - krapfever on Jun 23 2007 10:36:34 AM
 

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I would use the .5 pistons with new rings and get the motor back together so you can go racing.
Then I would build the spare motor(you do have a spare) with the s3 pistons, a really prepped cylinder head and a great intake and exhaust. That way as you get to the point where motor is the issue you will have one ready to go.
Like I always say get yourself some parts bikes. If you are racing I say get at least 2 more spares to go with your race bike.

Ken

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Vintage racing - old guys on old bikes
 

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Discussion Starter #4
Thanks, guys.

Yeah, I've got plenty of spares. This set of jugs was the best of the lot. The scoring on one of the cylinders was pretty bad after all.

Did some horse trading and the jugs are gonna get sent to BoreTech with the s3 pistons. If and when I do step up, I'll probably try to go CB175 (5 spd tranny), so the s3 pistons weren't going to do me any good sitting there anyway.

Now I just gotta get to lapping the valves while I wait for my jugs...





Honda go sideways!
 

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Joe C, I don't think you've got that right. S3 refers to the 3rd oversize. Standard Honda oversize dimensions come in .25mm increments - so an S3 piston would be the 3rd oversize, or .75mm over. Your .5 pistons are S2. I should say, this comes from building CB450s - I don't know much about the small bore bikes, but I'd be inclined to say the same would be true, given that they've probably got even less cylinder sleeve to work with.

A
 

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i agree with xander.

4th over pistons were always 1mm over in my experience.

can we get a ruling on this?

texy
 

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I was thinking the same way as Joe. I think that when a piston is marked S3, that means 3mm over. Factory pistons go by .25mm and are marked .25, .50 etc. Aftermarket big bore kits use the S mrkings and Wisco uses decimal inches such as.020, .040 etc.

That is my understanding although I could be wrong.

Ken

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My take on that is it doesn't make a lot of sense, and here's why. Big bore kits are intended to boost the displacement of your engine - but what's the point of rebuilding for 1mm over? Conversely, if a big bore size existed at 1, 2, 3 and 4 mm, why would there be any market for S1-3? And if it's just to restore an engine to spec, who'd want to risk having to rejet to account for increased displacement?

S4 kits would presumably be 4mm over, but most cylinder sleeves haven't got 4mm to work with. Big bore kits are usually kind of strange sizes meant to get an engine in the neighborhood of a specific displacement - the big bore kit for 450s that Powroll made was 498cc at 73.75mm (3.75 over), though most people agreed that was a really bad idea without pressing a thicker sleeve into the cylinder.

krapfever - get out your mic and solve this for us, would ya?
 

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Discussion Starter #11
I mic'ed everything once already, but didn't write any of it down. The jugs and s3 kit I'm going to use went out to BoreTech last week, but I still have the .5 pistons and some huffed jugs and pistons in my spares pile. I'll check it out tomorrow when I get back out to my shop space.

Funny, I've been asking around and everybody seems positive about their answers...but everybody's answer is different.

In a way I'm kind of glad I'm not the only one confused by this. I was beginning to feel stupid.



Honda go sideways!
 

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Krap,
S3 pistons ARE 3mm oversize, big bore kit pistons. They are actually 12th oversize in OEM jargon.

There a ton of the old S3 big bore kits floating around for the 160's, they come up on ebay all the time. There are also S3 kits for 175's but the pistons are such crap that I ended up designing my own. I can't speak about a 160, but on a 175 the S3 kits actually lowered compression from stock....which was already quite low. The 160 has a smaller combustion chamber than the 175 so it's possible compression would be acceptable on your engine.

Check the valve to piston clearance well....the S3 kit I bought and examined the valve reliefs in the piston where about 5 degrees off perpendicular with the wrist pin and a high lift cam would have caused the edges of the valves to nick the edges of the valve reliefs.

The typical S3 kit can be identified by a fairly rough top casting ont he pistons and usually teflon buttons to retain the wrist pins. There may be some "ART" piston kits out there....which are good pistons.

The engine will make decent low end power but will fall off rapidly at higher rpm due to the small valve/port size on the 160 head. Run the piss out of it and it will go pretty good.
JohnnyB
 

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Discussion Starter #13
JB:

Yeh, I'm using an ART kit.

So, lemme get this straight:

.5 is .5mm over (which is actually the 2nd oversize kit with .25mm being the first).

1mm over is an s1 kit, then there are 1.25, 1.5 and 1.75mm overbores before we get to an s2, or 2mm kit, and so on.

Makes sense.


Hmmm, that being the case I can see where the flow charactersitics would be affected by a fairly drastic overbore and stock valves.

Thats alright. I just wanna get the damn thing out on the track.





Honda go sideways!
 

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My last entry into this debate:

http://cgi.ebay.com/ebaymotors/Genuine-Honda-CB72-CL72-Piston-Ring-Set-0-75-NOS-S3_W0QQcmdZViewItemQQcategoryZ35595QQihZ019QQitemZ4616830924QQrdZ1QQsspagenameZWD1V

http://cgi.ebay.com/ebaymotors/GENUINE-NOS-SUZUKI-T250-PISTON-1PAIR-S2-0-50MM_W0QQcmdZViewItemQQcategoryZ10066QQihZ004QQitemZ140133894239QQrdZ1QQsspagenameZWD1V

http://cgi.ebay.com/ebaymotors/NOS-VINTAGE-HONDA-PISTON-CB125-S-S2-1975-1985_W0QQcmdZViewItemQQcategoryZ35595QQihZ002QQitemZ4629149722QQrdZ1QQsspagenameZWD1V

...all of which mark S sizes in .25mm increments. I can't imagine why any company would stamp big bore pistons with "S3" unless they were incremental oversizes of big bore (i.e. big bore kit at 54mm, S1 at 54.25, etc). If they were calling a 54mm big bore for a 50mm standard bike S4, they're just confused.

Alex
 

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Discussion Starter #15
Oh, boy.

Okay, if the volume of a cylinder is found using the formula pi X r^2 X h and the cheapo s3 Hap Jones kit I put in my 350 took it from stock 325cc to 362cc (as was claimed by someone I knew along the way), which was it, .75mm over or 3mm over?

Does anybody know the stroke(a.k.a. h) on a stock 350 piston? That is, if cc's are determined by the stroke of a piston and not the total height of the (empty) cylinder.

If so, solving for r plus .75mm or r plus 3mm and determining which value produced 362cc would solve the question.

It's been so long since I did my 350 I can't remember the measurements off the top of my head. Hell, I probably just handed the kit to the machine shop and didn't give it a second thought anyway.




Honda go sideways!
 

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Actually...I was on drugs...Xander is correct.
3mm over is called S12.

Don't know what the fuck I was thinking.
12 x .25mm is 3mm.

S3 should be .75mm overbore.

My bad.
JohnnyB

PS. So also ignore my comments about power and flow...0.75mm should have a fairly negliable effect on power. ART pistons more than 1mm oversize are pretty rare. I've seen a few 2mm oversize ART kits....I've heard the 3mm oversize are made but have never seen one. ART was the OEM supplier for Honda pistons....way better than the Hap Jones kits.




Edited by - jbranson on Jul 01 2007 8:21:38 PM
 

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It's a bit of an odd question, presuming the answer you're after isn't "millimeters." Stroke is twice the distance between the centerpoint of the crank (on its rotational axis) and the centerpoint of the crank offset - or, more easily visualized, the difference between the piston position at bdc and tdc. It doesn't generally need to be measured - it's a constant spec, and doesn't change unless you've done something really cool or fantastically unfortunate.

A
 

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quote:
It's a bit of an odd question, presuming the answer you're after isn't "millimeters." Stroke is twice the distance between the centerpoint of the crank (on its rotational axis) and the centerpoint of the crank offset - or, more easily visualized, the difference between the piston position at bdc and tdc. It doesn't generally need to be measured - it's a constant spec, and doesn't change unless you've done something really cool or fantastically unfortunate.
Stroke is the distance from the center of the big end to the center of the crank.
 
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