Compression low after fresh rebuild?

[kd460]

Not sure if this is an issue or not. Mentioned in previous posts, stihl 028 that had the piston installed wrong from previous owner.

Put in a new tecomec cylinder/piston kit (super). No real issues installing. For the heck of it, I checked compression prior to first start after rebuild and got 130's.

After running saw enough to make a few basic adjustments and cutting a few rounds to put some load on it (total about 1/2 hour run time so far), I let saw cool down and have checked compression again. Stil no real change in compression pressure.

Gauge has been checked for accuracy and is fine. It is the type with the schraeder valve in the part that threads into spark plug hole.

Pulled plug and muffler, everything looks fine in the cylinder. Starts right away, runs good, feels strong, cuts well. Running adjustments a little rich and gas/oil mix a little rich. Made a few cuts this morning to get things wrmed up and checked comp. again, no real change.

So am I just rushing things and numbers will climb as everything seats itself? Not really sure what else it could be. Should I even expect higher compression numbers? Seems a little confusing to me. KD

 

[Sethro]

How many times are you pulling it ?

 

[kd460]

anywhere from 6-10 or till the needle stops moving.

 

[Sethro]

If it runs good and starts good.I not forsure but 130 is'nt a bad number.But usually 4 pulls with WOT is enough

 

[Lakeside53]

It should be in the 150's... Maybe higher afer a few hours. Did you put in the correct (0.5mm) cylinder gasket?

Are absolutely sure that the super cylinder/piston is compatible with the version of the 028 you put it on?

 

[kd460]

Thanks for the replies, I just went out and measured the cylinder base gasket (I bought two from stihl dealer), it measures .52, so gasket is correct one.

Lakeside, please clarify compatability? If your talking about bore size in the crankcase, yes there was room for the larger piston. Nothing hanging up when I turned engine by hand after new cylinder was placed (before starting).

Just gonna run it for awhile and see what happens, still has me wondering. KD

 

[kd460]

Turns out a bum gauge. It is the type of gauge that has the separate hose that threads into the spark plug hole, and a quick connect at the gauge end. When I borrowed th neighbors to check accuracy, I switched gauges and not the section of hose.

I bought a new gauge today, and have about 148 to 152 with very little run time on the saw. Turns out the schrader valve in the hose (at the spark plug end) was flakey. Guess it just got old. I changed out the schrader valve for another I laying around, but they are different from regular car tire or a/c types. They are the same size and threads, but different colored "bands" on them. Turns out they all have different presure sensitivities and ratings. I think the color band on the schrader valve tells the difference/values.

FYI, the ones I had for ac work are red, the ones from the tire valve are black, the ones in the old comp. gauge are orange, and the one in the new compression gauge are light blue. The orange and light blue are very easy to push in with your figer, the ones that are black and red are harder to push in. The black and red ones gave much lower readings than the orange and light blue.

But, happy to say saw/rebuild is fine. Thanks, KD