Low compression on scrambler 50

Are you holding the throttle open? Check it with another gauge to verify it's not a faulty gauge or leaking connection to the gauge.

Thanks Latebird, for your reply. It is WOT when testing the compression and I testing the guage on my golf cart and it tested 130+psi as it should. Not sure what else to check. I did install the new head and gasket with the same results, about 20 or so psi. I have changed the head gasket several times and scared now that the bolts may ring off if I continue. I am torqueing the head nuts to 168 inch pounds/14 foot pounds each time. I did get the piston, rings and cylinder as a set from ebay and they looked ok. Maybe another better quality set may be the answer. I am not familiar with the scrambler 50 and just looking for any paculiararities that may help. I am about ready to order another piston, rings and cylinder. Any suggestions as to what is a good quality brand besides Polaris? Is Niche brand ok?

Only the piston, rings and head gasket have have anything to do with compression. Other than that it's the length of the stroke.

It's obvious you have limited engine technician skill.

As you have found out, installing a new head did not change the compression - when you installed the new piston, did the top of the piston come to the top of the cylinder at TDC?

latebird said:

Only the piston, rings and head gasket have have anything to do with compression. Other than that it's the length of the stroke.

It's obvious you have limited engine technician skill.

As you have found out, installing a new head did not change the compression - when you installed the new piston, did the top of the piston come to the top of the cylinder at TDC?

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As I mentioned, I am not familiar with the quirks of some of these small engines but even though not a "professional" mechanic, I have built and rebuilt probably 8 or 10 car and motorcycle engines over the span of 50 years or so with success. So, I am not completely unfamiliar with engines. I am sure you have heard of a "warped" head on engines before thus the reason for installing a new head and gasket.
All that aside, I did more compression tests with the carb and reed valve removed and still only geet about 15psi.. I have done nothing to change top dead center as the piston does come to the top of the cylinder as it should. The new piston looks identical to the old one. Also, before the original teardown, there was only 30 psi. Thanks for your help and replies.

Are you sure you got the piston in with the correct side toward the exhaust?

latebird said:

Are you sure you got the piston in with the correct side toward the exhaust?

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Yes. The arrow is pointed toward the exhaust, like the original piston position. I feel like I am just overlooking something. Only getting about 15 psi. on numerous tests at WOT and even with the carb and reed valve removed. This is really becoming a challenge. Thanks again

No - that is not right and the gap appears to be larger than .012 - was the ring squared to the bore using the piston to push it into place?

Yes, I squared both rings with the piston. The original gap was smaller and appeared that the ring ends were binding when installed in the piston so i filed them a bit. A video on the Niche site "how to install pistons on a two stroke " indicated the gap should 0.24 to 0.26. I will order another set of rings and try again. Now, to find some good quality rings and probably a piston too. Thanks

Typical new ring gap is about .012 to .015" on a 50cc two stroke with a service limit of about .024 to .030"

latebird said:

Typical new ring gap is about .012 to .015" on a 50cc two stroke with a service limit of about .024 to .030"

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Gotcha. Will gap as you seggested when I install the new rings.