the most worn (but functioning) top end

[eliteguy50]

I checked compression on a scoot and it was 60psi. This shocked me because the manual (page 6-9) lists compression for an sb50 at 142psi. It had no trouble starting and idled well but it was really slow acceleration and had no top end. This was on a sb50p.

So I was wondering what is the lowest compression anyone has actually seen work? what model was it?

The most miles anyone has seen on a single top end (still operational)? what model was it?

As you can see, curiosity has the best of me.-thanks

[wiguy05]

My 1986 NQ50 had 12,008 miles on it before I rebuilt it. Had roughly 90psi at the time too!

[Kenny_McCormic]

I have run briggs engines that burned 20-50 like a freight train, they ran great but when you need oil before a tank of gas is gone it isn't economical to run em anymore.

I also took a leafblower that had been run on straight gas(2 stroke) it wasn't locked up but the damage was horrible, I honed most of the scoring out, sanded the piston, filled out the smeared ring groove, installed a new standard size ring and it still runs great today. I don't even want to think about what the piston clearance is.

[DandyDan]

I've seen 75-80psi on an '83 Yamaha Riva 80 / Beluga. Someone had rebuilt it with a 1mm oversized piston but used stock rings so the ring cap was like 3mm

[burnt_toast]

Had a cracked/broken ring in my black 94 S and rode with it like that for at least 100miles (ignored sound figuring might be bearings.. lol) and she still rode like a champ!

never checked compression but quite sure it was pretty worn

[wikked_spree57]

My 1987 SE50P I put the Dio motor on, that tired Dio was running on 40PSI and it ran PERFECT... I don't know how, but it ran good. A little sluggish but good.

[Dac]

Had a cracked/broken ring in my black 94 S and rode with it like that for at least 100miles (ignored sound figuring might be bearings.. lol) and she still rode like a champ!

never checked compression but quite sure it was pretty worn

dude, you got to be careful. i did that for like, 50 miles. just ignoring the sound. Then the ring busted up and tore my whole top end up. It even ruined my head.
{ill post pictures once i get on my laptop}

[burnt_toast]

Had a cracked/broken ring in my black 94 S and rode with it like that for at least 100miles (ignored sound figuring might be bearings.. lol) and she still rode like a champ!

never checked compression but quite sure it was pretty worn

dude, you got to be careful. i did that for like, 50 miles. just ignoring the sound. Then the ring busted up and tore my whole top end up. It even ruined my head.
{ill post pictures once i get on my laptop}

oh no doubt, thats what ended up happening

the cyl was toast, the piston was burnt and together they fused to make me who I am today

ughh yeah.. sanjuro hooked me up with a ridiculously cheap topend and coupla slaps around and bugga was up 2feets again

[eliteguy50]

Dac wrote:
burnt_toast wrote:
Had a cracked/broken ring in my black 94 S and rode with it like that for at least 100miles (ignored sound figuring might be bearings.. lol) and she still rode like a champ!

never checked compression but quite sure it was pretty worn

dude, you got to be careful. i did that for like, 50 miles. just ignoring the sound. Then the ring busted up and tore my whole top end up. It even ruined my head.
{ill post pictures once i get on my laptop}


oh no doubt, thats what ended up happening

the cyl was toast, the piston was burnt and together they fused to make me who I am today

that is how I bought mine...here is one of the pistons
http://img200.imageshack.us/img200/9977/img3022.jpg
http://img195.imageshack.us/img195/8817/img3023o.jpg

once I broke it loose it had about 30psi compression (with oiled cylinder) but didn't run.

[808BMW]

I've soft-siezed this stock bore about 10 times, including 2 more just today

Carb is apart now waiting for a jet.

[burnt_toast]

soft seize on stock bore whatdaheck lol

[808BMW]

Yeah, it was doing it the last time I had my bike running (only I didn't think it was that at the time) and I decided to test it out today.
Gave it a good stretch at WOT and sure enough it died on me.
I cranked it slowly with the kicker a few times on and off for like 2 minutes, then just chilled for a few more. Gave it a kick, started right up, and I just cruised it back home real easy, it ended up shutting off right at the top of my hill and I coasted down.

Got to 45 going down my little hill just coasting, fastest yet!

[burnt_toast]

Sounds like you need a rejet, no reason for a stock bore to seize up at all. should be able to handle miles of WOT