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Top end rebuild

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im prolly gonna get a hell of a cussin for postin a 2-stroke/smoke question :cry: any way im puting a new piston and rings on my 1990 rmx 250 and on the instructions that i got with the weisco piston it said if i had a bridge in the exaust outlet that i had to drill lubrication holes in the piston. i am fairly mechanical and have never heard of this before. this is the first top end i have put on this bike and the old piston dosn't have any holes in it. help!!. thanx in advance :cry: :cry:

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You don't need to drill those holes. :cry: Been there, done that. But make sure the marking on the piston ring is facing UP when you put it on.

Should have no problems.......2 smokers Top-End's are very easy to do.

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You don't need to drill those holes. :cry: Been there, done that. But make sure the marking on the piston ring is facing UP when you put it on.

Should have no problems.......2 smokers Top-End's are very easy to do.

Are you sure, or are you saying that this year RM doenst require them due to no exhaust bridge? :cry: My brother in law put a top end in his old KX and didn't drill the lube holes that it said to drill. He had his Cylinder resleaved and everything. About 10 rides later the engine seized. When he tore in down the front of the piston and rings were melted. I was also on the All Things Moto Forum and read a post about this subject and quite a few people claim the same thing happened with there weisco pistons when they didn't drill the required holes.

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Very easy thing to do and see........does the old one

have holes. There you go......done deal.

Yea right mxchic about the holes.........are they would

not have said anything about them if there was not a issue.

Every piston comes with instuctions and it sure does say to drill the holes. That is for the Older bikes.....as for 90' cr250......no holes.

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If you have a basic manual you should'nt be to confused??. But don't forget to pay attenntion to the power valve assembly??. :cry:

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You don't need to drill those holes. :cry: Been there, done that. But make sure the marking on the piston ring is facing UP when you put it on.

Should have no problems.......2 smokers Top-End's are very easy to do.

What happens if the marking on the piston ring isn't facing up??

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What happens if the marking on the piston ring isn't facing up??

Good question.......I have always been told for yrs. and

yrs. to do this and plus the instructions inside the Piston

say to do it too. Now if you don't do it.........I would

think it would lock-up in 5 min. after rebuild. Most likely

the bottom or top(maybe both)of the Ring are cut a special

way so the ports don't cut into it. I sure have looked at

the Rings before and they do look the same on the top and

bottom, but better safe than sorry. Plus, I've done over 50

top-ends(maybe more)and I have always done the markings facing up.

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Does it matter on 4 strokes?

From what I've read on the crf forum, I believe yes, you do

have 1 ring that does have a mark it needs to be face up.

I have not done any 4-strokes before myself, so maybe put

that question on the crf forum. My 02' crf450 has over 310

hrs. and have Never even had to check the valves, to say the

lest of even taking spark plug out. :cry: My 03' crf450

has over 90 hrs. and the same as the above on the valves and spark plug. What valve problems here on the crf450..... :cry:

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Wiseco knows bikes & their products a lot better than anyone on this forum will & if you have an exhaust bridge & they tell you to drill holes in your piston to lube that bridge you really have no reason not to. Those holes are drilled to lubricate & cool the exhaust bridge. An exhaust bridge is the hottest spot in a 2-stroke & that's why bridged port 2-strokes normally melt down & seize there. Drilling the holes Wiseco specifies has been standard practice for racers with bridged exhausts for decades. I know it was an old trick when I began doing it to my bikes in the mid '70s. It gives additional time/protection against seizing & is very simple & free insurance. When done properly it might help you but defintiely can't hurt anything so there's really no reason to debate it, as they say "Just do it!". Air leaks & other lean conditions are the most common cause for seizes so if your bikes seized make sure it's sealed up before you fire it up.

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