The new Kid In town

[texas_bugeye]

There’s a new Old car in town! A neighbor a few blocks down the street stop by in his new car a 61 sprite . Great way to meet your neighbor! appears fairly solid and complete it was owned by a kid with little experience and bit off more than he could afford. It runs pretty good . but when he told me the cylinder pressurest it kind of shocked me (I should check mine)1=65 2=65 3=63 4=59 he took these readings a few nites ago with all the plugs removed and the throttle closed. There pretty even but man that seems low. I helped him do a valve clearance test and when we did they were really tight like nearly no clearance. After adjusting it sounds like a singer sewing machine makes me smile. So we did another test and it came up the same. Car runs great but should the compression be a concern ? It has the normal leak at the scroll but nothing excessive and oil looks ok power seems to be on the low side and it feels like there’s no timing advance. You know.. flat. Could the cam sprocket be Off a tooth? The crank pulley – dampener has no markings! So how do we establish TDC we could measure the spacing to get advance off of my cars marker.
Thoughts on the compression
Thoughts on the flat power
Bad Cam?
I forgot to say that the engine has abou 3000 miles after the kid rebulit it.

 

[racingenglishcars]

Check the guage.
I don't think an engine will run with such low compression.

 

[texas_bugeye]

Yea I expected about 120 PSI.
well the valve adjustment does appear to have made a change.
I noticed that when we pulled the plugs last nite that the plugs were sooty on 1&2 3&4 were a nice tan. Now today all 4 are tan. and now it seems to pickup RPM's quicker when you blip the gas.Could the valves have been not closing all the way? Geez you would think it would run rougher heck if that was the case.If at all. but then again it was so perfectly way to tight maybe it did run evenly bad.

 

[Bugeye58]

I'd re do the compression test with another gauge.
Jeff

 

[texas_bugeye]

does it matter if the carb is at idle postion or wide open?

 

[Bugeye58]

General wisdom specifies that the throttle be held wide open. I've never done an A to B test to see if it makes any difference, but always do mine at WOT.
Jeff

 

[Glen_B]

Butterfly open or closed, the reading will come out the same. You just have to turn the engine over longer to get a full reading when the baffle is closed. A few rotations is plenty with the butterfly open. Five or 10 when shut.

Glen Byrns

 

[texas_bugeye]

I have a 0-200 Psi Ashcroft gauge I'll put it on the hose and check assembly and we will try it tommrow afternoon. Its gota be at least 100!

 

[Bugeye58]

Make sure the valve core in the end of the hose is fully functional.
Jeff

 

[jlaird]

I got 125 in all but I think my guage needs renewed as well. Read low when I did the race car as well, about 35 lbs low when compaired to another guage.

 

[texas_bugeye]

Good point on the valve core. Is it just a standard type you find in tire valves or is it different. If its the same I'll replace both in the cylinder end and the tee bleed.

 

[Bugeye58]

Here's the definitive answer on compression gauge valve cores, from our own Dave Russell. Once again, Dave, thanks.
Jeff

Just a quick note on compression tester calibration.

I was recently doing a quick compression check on a new engine. I ran through the cylinders the first time & was getting a pretty even 190 psi. In the middle of a second test, the gage failed to hold the readings, leaked down.

I replaced the Schrader type valve in the tester with a standard valve stem. The readings dropped to around 135 psi. After much studying, I found that valve cores are not all the same. Collecting a few different types of valve cores, checking the compression tester readings, & measuring the actual tension required to open the various valve cores, I found the following.

Valve cores marked with a red band, standard tire type:
Pull tension - 56 ounces.
Compresion gage reading - 135 psi.

Valve cores marked with an orange band, usually used on air conditioning applications:
Pull tension - 2 ounces.
Compression gage reading - 185 psi.

Valve cores marked with a white, clear, or black band:
Pull tension - 1 ounce.
Compression gage reading - 190 psi.

In checking around, I found one local Carquest dealer who looked up & ordered valve cores for Lysle compression testers. Part number STL20100, black marking band. They work as expected. Compression readings back to the original 190 psi. The orange band air conditioning type cores are very close to correct & easy to obtain. I find that the air conditioning type valves actually hold pressure more reliably than the "special" Lysle valves.

I'll bet I'm not the only one to be perplexed by this problem, or to
buy a new compression tester when the previous one failed to read
properly. It's pretty obvious when you realize that the gage can only
read what is "left over" after it goes through the valve core.

 

[texas_bugeye]

well THERES your problem!!These are red banded I asked were they were from and sure enough he told me the old ones leak so I took some off two tires in his shed. I think I may invest in my own unit as I thought about borrowing his.
The info on the schrader valves.. man I sure you saved me alot of time and heart ache thanks again.

 

[jlaird]

What can I say but again the forum provieds info that is just not available elsewhere.

Thanks folks, will look for a new valve.