BannedCR500Riders.com

Here are a couple pics of the piston from my 500. There is obvious worn ring issues. My question is would you replace this piston or just rering? The cylinder looks great - no scoring at all.

Piston looks usable, but what is more important is what it measures compared to the bore.

I need a bigger monitor.

Measure the cylinder and piston, only way to know fer sure.

iggys-amsoil wrote:I need a bigger monitor.

Measure the cylinder and piston, only way to know fer sure.

I left the images large to show detail - my monitor is 46" though. LOL

What are you using for filter oil?

Wesson?

I'd start over.

AlisoBob wrote:What are you using for filter oil?

Wesson?

I'd start over.

I have not rode this yet - just finished building and done a compression test and then tore it down. It seems there is was a lot of blow by. The cylinder to piston clearance is within spec but on the higher end of spec. The ring end gap is much larger than spec.

I'd start over too.
I'm not the sharpest knife in the drawer but, the highly specific blowby suggests a problem somewhere.
To me, a new topend is cheaper than a new engine.
I'm getting ready to do it to my 480.

blowby looks strange, is that the result of the dreaded stop sign bore?

Kuma wrote:blowby looks strange, is that the result of the dreaded stop sign bore?

Not sure - there is blow by on each side of the piston - around the wrist pin area and also some towards the intake / carb area. I measured the bore though and it does not seem off. Tomorrow I am bringing the cylinder to my father's house the cylinder to confirm the bore with better equipment. If it needs a bore I will just sell the bike for $50.00 and a case of beer.

So, it's 1.00 over?

Tharrell wrote:So, it's 1.00 over?

Yes it is so no problem boring. The problem is I live where a good machine shop is hard to find - may need to send it away for a good bore job else risk letting the local yahoos play with my cylinder. Ironically I just got back from Boston - should have taken it with me and had it done there.

Shipping within Canada sucks! Overpriced an slow!

That said for someone who seems to have a grasp of what's needed to be done right on these, Roosty seems to be the guy if you need to ship it anyways.
I went local and am happy with my results so far, but if I didn't have someone nearby I trusted it would have gone to Millar (Roosty) if for no reason than he seems committed to the cr500 for the past and future

Roosty seems to be the guy if you need to ship it anyways

roosty delivers far better than oem work

2strokeforever wrote:

Roosty seems to be the guy if you need to ship it anyways

roosty delivers far better than oem work

I PMed Roosty about it.

Bore was within spec in terms of being round so I cross hatched it and ordered a new complete Vertex top end. I cannot wait to try this beast with a new top end. The old piston will be a pen holder at work. :-)

Did you get a compression reading on the old top end?

Yes it was 60 - the ring end gap was over 1mm - rings were toast. The moron I bought it from on eBay said it was just rebuilt but thankfully all it needs is top end or so it seems. It has a brand new right side cover / water pump which is great since it is the MG one.

Well, that's the blowby explanation.
I can hardly believe it ran at 60psi!
I would certainly replace the whole top end if it were me.
But then, I would probably redo the crank just to be sure as well.
If you caught Doggers rebuild thread, that's about how bad I have it.
It's a very informative build as well as the others on here.
Good luck and keep us informed. Tony

I had it started once but man was it hard to get going - I knew at that point something was wrong. I am waiting for the parts to come now. The crank checks out fine as far as the tests I have done. We have a short summer here and I really want to get this thing running. This winter I think I may split cases etc and I have a few upgrades I want to do - ex. newer style wayer pump cover to replace the MG one.

I installed a complete new Vertex top end tonight. I started late so I have to finish tomorrow evening. I cannot wait to try this bike - I even took Friday off to tune the bike in.

What are the clearances?
What about the crank seals?
A compression and leak down test would be great after the rebuild too.

Tharrell wrote:What are the clearances?
What about the crank seals?
A compression and leak down test would be great after the rebuild too.

Piston to cylinder clearance is fine - top end feels much tighter - I think the wrist pin bearing was really worn. I will perform tests once the engine is fully assembled - hopefully tonight but never can tell when you have four year old twins in your care.

4 year old twins?
How do you get ANYTHING done?

Tharrell wrote:4 year old twins?
How do you get ANYTHING done?

x491

MojoScojo wrote:

Tharrell wrote:4 year old twins?
How do you get ANYTHING done?

x491

I got to say I enlist a little help from Budweiser at times.