Questions for those who have done ring jobs

[OlderHuskyRider]

I have boxes of "used but trusted" parts , I'm willing to sell to you at a good price !!!

If they are about to fail, they should be worthless, so I'll take 'em for free.....

 

[Tinken]

$315, ouch. I had 8000 miles on my KTM 500 and the valves and the piston looked good so I just put new rings and valve guides in. If your piston isn't gulled and meets bore specifications, plus wrist pin is tight, you don't have to change it. If you see any heat or stress cracks/fractures, I would go ahead and replace it. All engines have blow by, it will never be a perfect seal. Your blue smoke on acceleration is likely a leaky valve guide/seal.

 

[DG Harv Serv]

If they are about to fail, they should be worthless, so I'll take 'em for free.....

Thats my point !!!

Do whatever you feel is best ! Good Luck !

 

[OlderHuskyRider]

$315, ouch. I had 8000 miles on my KTM 500 and the valves and the piston looked good so I just put new rings and valve guides in. If your piston isn't gulled and meets bore specifications, plus wrist pin is tight, you don't have to change it. If you see any heat or stress cracks/fractures, I would go ahead and replace it. All engines have blow by, it will never be a perfect seal. Your blue smoke on acceleration is likely a leaky valve guide/seal.

Thanks for the input and experience on your 8000 mile 500cc, it makes me feel better about my decision. Did you do valve guides (pretty involved job) or valve guide seals (easier)?

 

[R_Little]

If I order a standard size OEM piston, will it fit my bore the way it should or is it possible that the piston will be smaller or larger and require me to get a build-up or grind-down job done on a Nikasil cylinder?

Good question. Not all pistons are machined exactly the same size...husky offers A/B/C sized pistons for the 2-Strokes each a touch larger then the other. Some times an old part is more reliable than a new one. Sometimes a new part just isn't made right. When I rebuild a motor I'm the most nervous when I start it for the 1st time. That "new" piston can be cracked from the factory or handling.

That is why they have specs on component wear. Frankly, I've never seen a 4 stroke piston explode, 2 strokes yes. 4 stokes usually toss the rod bearings when they go.

 

[OlderHuskyRider]

Good question. Not all pistons are machined exactly the same size...husky offers A/B/C sized pistons for the 2-Strokes each a touch larger then the other. Some times an old part is more reliable than a new one. Sometimes a new part just isn't made right. When I rebuild a motor I'm the most nervous when I start it for the 1st time. That "new" piston can be cracked from the factory or handling.

That is why they have specs on component wear. Frankly, I've never seen a 4 stroke piston explode, 2 strokes yes. 4 stokes usually toss the rod bearings when they go.

Damn good stuff there, I bolded the comments I agree with pretty strongly. Thanks for the post.

 

[Tinken]

Did you do valve guides (pretty involved job) or valve guide seals (easier)?

I was a professional motocross mechanic for years, so I was comfortable with drilling the old guides myself, but it isn't normally a job for the home mechanic.

 

[R_Little]

Damn good stuff there, I bolded the comments i agree with pretty strongly. Thanks for the post.

It's different for different bikes and displacement too.

On a 450 a bit of extra ring end gap doesn't really matter as it has plenty of power and 3 sets of rings. My Yamaha 444 smokes a touch when cold.....so what? It still runs as hard as any big bore bike I've ridden.

OTOH, On a 125 you want a good tight ring or you loose power you can feel.

For example my 135 was running weak so I took it apart last week. I have a new piston and ring on the bench but the piston and ring were tight so I just put it back together. As for new parts this is a case in point: The "new" ring had .014 end gap and the 2 yr old one had .012" so I reused the "old" one.

Turns out the power loss was due to a loose PV shaft.

It runs hard again now.

 

[Slowpoke]

Curious as to how many hours you have on the bike in addition to knowing the miles.

The odds of having a problem with a new 4t piston are pretty much zero. Worrying about it is really just a waste of time. These things are forged and machined from billet & they just don't fail.

Keeping your 10,000 miler is something you really should be worrying about. These pistons have a very limited wear surface and small skirts and yours could very likely be worn such that your piston is now rocking in the bore. This often happens after the motor has about 250-500 hours, or about 5000-10000 miles. (depending on riding conditions)That slight rocking motion is very likely also contributing to your blowby and oil use. It's also hard on the Nikasil coating as it causes uneven wear patterns. This could result in you having to spring for a several hundred $$ re-coat, as opposed to a 50$$ hone job. If the Nikasil gets too thin in spots it can start flaking off, which is terminal for your engine.
The rocking will only get worse at an increasing rate. Trying to save a couple hundred $$ and sticking with the 'known' is false economy thinking. You're also setting yourself up to spend 2x as much on gaskets by having to take the motor apart an extra time.
Honestly at 10,000 miles you really should also be looking at the crank and rod bearings as well.

The husky big block motors (like what you have) generally have decently long service lives, especially compared to many of the jap 4ts and some KTMs, but they don't go forever.

 

[ghte]

Which ever route you take please look at the valves and valve seat and check the timing chain