Engine Rebuild

[krapfever]

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

[joe c]

.5 is .5mm, s3 is 3m over.

jc

[kenessex]

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

AHRMA 412
Vintage racing - old guys on old bikes

[krapfever]

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!

[xander450]

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

[texmawby]

i agree with xander.

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

can we get a ruling on this?

texy

[krapfever]

Tex and xander:

That seems to make more sense based on the measurements I was coming up with.

Honda go sideways!

[kenessex]

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

AHRMA 412
Vintage racing - old guys on old bikes

[parks61]

what kenny said.
parks

[xander450]

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?