As stated in earlier threads, I have done a top-end rebuild to cure a leaky base gasket. Honed cylinders, new rings, valve re-grind plus all gaskets. Also fitted an EV27 cam, (which I am delighted with).
Now after about 100 miles or so, on idle it smokes a little bit so I decided to do a compression test.
My Clymer manual says 90 psi is normal, I am getting a reading of 165 psi, both cylinders within a lb or two of each other, so, of course, I am chuffed.
But if 90 is normal why am I so much higher?
The engine is standard with standard size pistons, no re-bore or anything like that. As I said, only the EV27, an S&S super E and Scremin eagle ignition coil module.
Does the cam make a difference?
Thanks.

Tony.

 

Maybe the gauge is wrong, I'm running weisco 9.5 pistons and EV 27 cam, and I'm sure my compesion was 125-130 psi range last time I checked. So one of us has a faulty gauge.

 

I wouldn't be concerned about it. The more import measurement is the no difference between cylinders. 90 might be borderline acceptable, that is, if it's 90 you can get by without a rebuild. 160 is more "normal" for a typical motor, not necessarily a HD. And, as SG states, everyone's gauge is different to some extent or other. Mine, for example, just presses a rubber stopper against the spark plug hole. My other compression gauge, the one I always carry with me, is my thumb, and calibration on that one is not too close, but it's always "handy." It has more of a binary calibration: Has compression, doesn't have compression.

A cam will make a difference in the compression reading. A big cam can give you lower readings on the gauge from valve overlap.

 

Thanks for replies.
Should have said tried two different gauges. One was screw in type, (like a plug) that gave 165 repeatedly. The other was a push and hold on type, (no, not thumb!!!) that gave a slightly lower reading, 155 lbs which I put down to the fact that it is hard to hold on.
As Dr.Hess said, as both are more or less same I will not worry.
Tony.

 

Also, the timing of when the intake valve closes will effect compression readings.
Early close = higher compression reading.

Yours seams normal.
Hopefully the rings will seat better with time. Shouldn't be smoking, unless you put one of the rings in upside down. Does it smoke both cylinders?

 

EV27 is a compresson builder so your compression sounds normal, with the compression ok you wouldn't think you have oil getting past the rings. I believe you mentioned earlier that you installed a Super E with the rebuild, is it possible the idle circuit is alittle rich and the smoke you notice? if I'm wrong on the carb install, please disregard.

 

Good point. He never did say what color the smoke was.

 

No, I always had Super E.
I suppose smoke would be a bluish color and is same from both cylinders.
Now it's not much, but noticeable only on idle. It goes when engine is revved and not there at all while running under load or on over-run, (de-cellerating).
Tony.

 

I had a smoke issue a few years ago on my EVO when I put in an EV27. After running a couple hundred miles I have some blue-ish smoke. It turned out to be valve guide seals. All I could come up with is that the EV27 had ever so slightly more lift which pushed a previously un-wiped / rougher portion of the valve stem into the seal causing it to damage the seal enough to allow oil through. I had to tear into it.

Ended up boring the cylinders .010", new rings, valve job, port, shaved heads, new springs...got her back together and it still smoked. This time it was the rings that didn't take. I did a compression test and it tested fine...never did a leakdown test at that time. I had to tear into it...again.

Honed cylinders, new rings, put together with dry (no oil) cylinders and haven't had a problem since.

Not sure that helps at all.