'72 Jackpiner - Compression Check

[iyaoyas]

Can anyone tell me what the compression range is for a '72 KTM 175cc?  I measured ~68psi...

By comparison, a '72 Sachs 125cc measured ~115psi...

Thanks-

Stephen

[thrownchain]

68 lbs definately calls for an overhaul. Very good would be around 150 lbs. Give or take a few lbs.

[Larry Perkins]

You may know this but to get an accurate compression reading you have to hold the throttle wide open when kicking.  Continue to do so until guage won't go any higher.  IF you are doing it correctly both bikes are low on compression.  If throttle is not open it is an incorrect reading.

Larry P

[Kip Kern]

Don't forget to hold the kill switch on while kicking and having the throttle wide open!;)

[firstturn]

Kip,
  Is that what the knobby mark was going up the wall in my old shop?   []

Ron Carbaugh

[iyaoyas]

I did not hold the throttle open so I'll repeat the test again with this condition.  That said, does anyone know the compression range (psi) the KTM 125 engine should be within?  I understand 150psi is good but how good is good?

Thanks for the feedback guys-

[gooddirt]

Ground- out your spark plug to protect your moto plat. (or is that just a myth ?) I guess keeping the kill button does the same thing ?

[454MRW]

Yep, that's why you hold the kill button. It's awfully hard to get a bike to run with the compression tester in place of the spark plug. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S

[gooddirt]

Yes no doubt on that one, not all bikes have a kill button. And some folks don't know of moto plat safety tips. LG

[iyaoyas]

Ah Ha!  Learned something new regarding use of the kill switch to protect the motoplat ignition...thanks again!  Stay tuned for v_2 of the compression test results...

[Rain Man]

Is it better that the engine is warm first??  Of course thats if it will start.  My 73 JP has 128.2 lbs of compression, cold. And it runs great, still.

Raymond
 Down East Pentons

[David Laite]

That is low, not enough to fire on with the exception of maybe an older Briggs twin. My '73 Piner comes in at 126 psi for comparison.

1973 Penton Jackpiner
1982 Yamaha XT200
1982 Yamaha XJ650J Maxim
1987 Yamaha YZ490
2005 Honda CRF450R

[iyaoyas]

Ok...WOT, (kill switch engaged) compression as follows:

Jackpiner: now 85, was 68psi
A few comments:
- The piston was seized (several years) prior to the 1st test
- Carb was not installed, now installed 2nd time around
- Perhaps the piston ring remains 'stuck' within the ring groove??
- Will retest after I warm up the engine, that is if the engine starts...

6-Days: now 125, was 115psi.  Will retest after warm-up...


Berkshire (12 miles on DW rebuild - 1st over): 115psi  Will also retest after warm up...

Thanks again for the feedback!

-Stephen