Piston in good shape? How do i know?

dell30rb · May 20, 2002

I have approx. 30 hours on my bike. I have all the things necessary to replace the ring. I'm wondering If i sould just go ahead and do the whole topend when I open her up. The bike hasnt ever detonated, was run on castor 927 @32:1 with premium pump gas all of its life. Has never overheated and boiled over. I was wondering if there is a good way to tell if the piston needs to be replaced or not. My plan is this: Replace the ring now, go till the end of summer, then this fall I'll tear the whole thing down and do a complete top end, and get this thing ported by eric. Do you think that my current piston will need to be replaced before the end of summer? The bike is not running bad at all, oil was changed every 3 rides, and the air filter was cleaned after every ride.

I know the only way to tell if the piston is worn or not is to have a shop measure it (or do it yourself), but is there any way I can get around this?

Durt Cycler · May 20, 2002

I generally look for score marks, wear in the skirt and ring land area, and blowby damage. I never replace just the rings I just do the whole topend so I don't have to keep tearing the topend apart so soon.

dell30rb · May 20, 2002

I know, but I got the rings and a base gasket for free when i bought the bike. I'll look at the piston real good. I have looked through the intake port and saw no blow by at all, no score marks either. It looked like a brand new piston. (From the side).

jmics19067 · May 20, 2002

I will only put rings in in the middle in the summer and then do a piston in winter myself but I ride a 250 every other weekend on the average. I dont think your 80 is going to last the summer on one piston . The best way is to measure everything . Take a look at how much it would cost to get your cylinder replated, head resurfaced and splitting the cases to rebuild the crank. A very feasible cost if you let your piston go too long. Now take a look at how much it would cost to buy the tools to measure evrything and /or take the parts to someone who will measure it for you. Not only will doing it right be more cost effective but you won't be waiting around for your parts or machine work to get done if you grenade the engine.

Jaybird · May 21, 2002

Delve in, Dell....it's not as bad as you may think. A cheapo set of calipers and some feeler guages from Sears is all one needs to measure things. If you don't have the rest of the tools, just start making birthday lists. You'll be glad you know how to take care of your own stuff. Being dependant on a dealer or a shop is not a fun thing, nor cheap.

If "gettting around maitnenance" is what you seek...ride it till the hinges fall off and don't worrry about it! :)

MikeT · May 21, 2002

Jay, What would you recommend using to measure the bore? I might just buy one of those tools, but do they really sell a dial bore gage at Sears? Also I guess I would need a dial Vernier Caliper for the piston, correct?

jmics19067 · May 21, 2002

The next time your at Sears get the hand and power tool catalog every thing you could possibly need or want would be in there. non digital calipers 40$ digital calipers 150$ bore gauge 110$ . although the calipers are good I prefer to measure my pistons with a micrometer 4 pc set 0 -4 " 100$

WoodsRider · May 21, 2002

Personally, for the piston, I would buy a micrometer. Calipers are not that accurate when it comes to measuring diameters with such a tight tolerance. For the cylinder, a bore gage is best, but many people do not know how to set-up a bore gage properly. Using a known standard (setting ring) is the most accurate method, but you can use a micrometer if you're careful.

I've been involved with metrology, inspection, gage selection and gage r&r for a long time. I've seen good parts get scrapped and scrap parts get used due to inaccurate measurement techniques.

jmics19067 · May 21, 2002

Using a known standard (setting ring) is the most accurate method, but you can use a micrometer if you're careful.

curious& unfamiliar with how these two are done what is a setting ring? woudl / could you use a piston ring in non worn part of the cylinder measure the end gap, then slide it down to a worn area and measure the end gap.once you know your circumference then divide by pi x 2 to get the diameter? how do you use a micrometer to measure inside?

dell30rb · May 21, 2002

I have a feeler gauge already... What would that be useful for?

I've only used it to adjust the valves on the xr200.

Jaybird · May 22, 2002

I agree the best way to check bore is a bore guage. Ditto on the mic's.

Dell, use the feeler guages to check your ring end gap. This is very important for proper top end work.

Also, next time you have a question about plug perfomance or type...measure the gap before you post. :)

WoodsRider · May 22, 2002

Originally posted by jmics19067
what is a setting ring? woudl / could you use a piston ring in non worn part of the cylinder measure the end gap, then slide it down to a worn area and measure the end gap.once you know your circumference then divide by pi x 2 to get the diameter? how do you use a micrometer to measure inside?

A setting ring is a known standard available in different sizes and grades for accuracy.

Measuring piston ring end gap will only tell you piston ring end gap. Cylinders don't wear even, they end up more of an egg shape. Piston rings aren't perfectly round either.

If you set and O.D. micrometer to a known size, then set the bore gage (zero the dial indicator) to that size you can then measure with the bore gage.

MikeT · May 22, 2002

Originally posted by WoodsRider

A setting ring is a known standard available in different sizes and grades for accuracy.

Measuring piston ring end gap will only tell you piston ring end gap. Cylinders don't wear even, they end up more of an egg shape. Piston rings aren't perfectly round either.

I thought you were talking about "setting" a new ring in the bore and measuring the end gap. I have never heard of a setting ring either. Could you explain further.

jmics19067 · May 22, 2002

A setting ring is a known standard available in different sizes and grades for accuracy.

So for a lack of better words it is a machined plug of the exact diameter you want?

Measuring piston ring end gap will only tell you piston ring end gap. Cylinders don't wear even, they end up more of an egg shape. Piston rings aren't perfectly round either.

Your right I had a brain fart on the out of round , but what I was trying to ask is if you know the original circumferance of the bore and measure the difference of the ring gap between where the cylinder is worn and not worn. Kind of a foolish question though since not only cylinders wear in a cone shape but also in an oval shape.

WoodsRider · Jun 3, 2002

Sorry for the delay in answering, I was out of town on business.

A setting ring is also known as a ring gage, which is different from a plug gage. If you look up ring and plug gages in a McMaster Carr catalog, you'll get a better description of what one is.

jmics19067 · Jun 3, 2002

just happen to have my yellow hymnal right here

ahh hah I see what you mean now. too set your instruments to zero.

WoodsRider · Jun 4, 2002

jmics - Close enough. ;)
Are you going to make the Paragon trip on 6/22-23?

jmics19067 · Jun 4, 2002

I certainly hope so !!!!!!!! just so happens I was going to take off that Fri and Mon. for a long weekend since it is my bday Fri. If my honeydo list dwindles down to a day off and the planets are aligned properly. If I can and do make it though I have very little resources for roughing it out in the woods for a weekend so it will probably be only a day trip for Sunday.

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