Cylinder Height setup for 250 motor

[Big Mac]

I'm doing a top end rebuild on a '76 KTM 250 motor, and got a new Wiseco piston from Al B. to replace a Wiseco that came out. The Wiseco's don't have the Dykes "L" ring, so the cylinder deck height adjustment above the top of the L ring doesn't apply.

Does anyone out there have an old 250 Dykes L ring laying around that they could put the calipers on for a precise measurement on the height of the L? I'm hoping the Wiseco piston has the same location ring groove and I can do the math to match it up right.

Al B. said without a calculation of measurement off the ring, that holding the top edge of the piston down below the cylinder deck level the same .040" per the book was about right. I've got a .025" base gasket on now and the piston top edge is above the cylinder deck a smidgen already.

Thanks in advance for the feedback.

 

[Kip Kern]

I have run into the same at one time or another.  I will check out my 250 pistons and do a comparison measurement for you and get back with you.  Some of the older Wiseco's were also a single ring design and I have had to do the same on 175's/250's

 

[Big Mac]

Thank you Kip! A measurement of the L ring height AND a measurement from the top piston edge to, say, the bottom of the L ring groove on a stock piston...would be dead-on perfect! Might also help some other Wiseco top ende rebuilders too. Much appreciated.

 

[G Ellis]

250 L ring height is .050 to the top of piston. In my service book "X" height is .035 to .047 for 250's.Hope this will help.

 

[Big Mac]

Thanks Mr. Ellis. When you say L Ring height is .050" to the top of the piston, are you talking about height on the piston from bottom of the L ring slot to the top edge of the piston, or just the measurement of the height of the L ring itself? Thanks again.

 

[G Ellis]

I was talking about the top of the L ring. If you need the measurement to the bottom of the L ring let me know.

 

[Big Mac]

Got it, thanks. How about the measurement on height of the L part of the ring itself? Do you happen to have an old ring around to measure? Thanks

 

[G Ellis]

I was talking about the top of the L ring. If you need the measurement to the bottom of the L ring let me know.L ring measurement is .080 thick

 
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[Kip Kern]

Big Mac,  Give me a ring at 765-668-8038 (Indiana) and I'll try to help.  Sorry for the delay but have been busy on the Six Day Reunion bike!

kip

 

[Big Mac]

Kip-- thanks, but I think I've got this figured out, thanks to Mr. Ellis. For anyone stuck on this w/ Wiseco replacement piston: L height on the stock ring is .050", ring sits .080" from top edge of piston, so for .040" to cylinder deck height, piston top edge should sit about .010" below cyliner top deck at TDC. I got to this height using 2 different base gaskets for total thickness of about .048"--which is pretty darn close to the .040" (1mm) base gasket Al B. recommended to start with. I should have just listended to Al. Thanks for your help!

 

[G Ellis]

Big Mac glad to be of some help. You can address me as Gary, Mr Ellis makes me fill like I am getting old. I am only 44, hope that your 250 gets its life back in it again.