948? Compression Test

[erstearns]

Pulled the 948? engine out of '60 Bugeye restoration project car. The engine ID plate is missing. What should the compression test read? I got readings ranging from 170 to 190 psi. Seems pretty good for an engine that has not been run since the mid 80's or earlier. Any other way to tell anything about the engine without tearing it down? It has been out of the car before, it was pained robin egg blue. If nothing else it will have to be repainted the proper color.

 

[DougR]

Well ers, those readings sound very strong. Did you test both dry and wet? If nothing else, with the engine out, I'd replace the freeze plugs just on account of they're cheap and easy to do. It would probably be a good idea to positively identify the engine. Did you pull the engine and trans?

A fun project! Good luck!

 

[erstearns]

Test wet or dry? I tested as it sat after pulling. I assume that was dry. I did not introduce any fluid through the top end or through the plug entry. I was just trying to see if the starter turned the engine over and thought it was a good time to test compression. I pulled the engine and tran as one unit.

 

[spritenut]

Those compresion readings are great for that engine.
If you can crank it over, why not fire it up?
Yes even out of the car.
Hook up the coil, hook up an oil pressure gauge, run the hot wire from a jumper cable to the hot side of the coil (+ or - ground?)
Hook the hot jumper to the starter terminal, use the ground jumper and hit the ground of the starter to spin it over. Remove the carb float bowls, fill the bowls with fresh gas, have a fire extinquisher handy, set the gas can far away from the engine and fire it up. Keep a hand on top of the rocker cover so it doesn't jump all over or tie it down, they don't move that much but it could vibrate across the floor if it has a bad miss.
Do NOT run it very long with no water, when the floats are empty, that was long enough. Wait for it to cool completely before starting it again. Be sure to keep an eye on the oil pressure gauge when it starts.
I do this all the time and the old lady across the street loves watching an engine run while just sitting out side of the car on the garage floor

 

[erstearns]

spritenut, thanks for the reply. Many of my buddies that are american gearheads suggest getting the engine running while out of the car. Currently the engine is on a stand, I had to take off the flywheel to get the mounting brackets to fit. I may try to get another stand that will allow me to fire it up. I do not know the pedigree of the engine. It appears that it has not been run since the oil filter element was changed and new points, rotor etc were installed many years ago. With the engine being painted I assume that it had some work done on it back in the day but I do not know what. I cannot track down the past owner but I will keep trying. Thanks for the comments, I will try and fire it up.

 

[ThomP]

The spark plugs can tell you whether the engine was using oil. I have owned several engines that had good compression, and ran well but still burned oil. Give those plugs a good inspection any you'll know.

 

[Bob Claffie]

I once maade the mistake of bragging about how high the readings were on a compression check. Then a more experienced mechanic told me that the higher the reading the milder the cam! You get big numbers because the valves aren't opening early or fast and not going very high either. Best to check valve lift with a dial indicator to make sure the cam isn't overly worn. Bob

 

[erstearns]

Bob Claffie, thanks for the tip. I will check it out. At this stage I am trying to determine if the engine needs a rebuild and that was the first thing I checked. I will continue to investigate. Thanks again for the info.

 

[Dave Russell]

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by erstearns:
What should the compression test read? I got readings ranging from 170 to 190 psi. <hr></blockquote>

ERS,

Readings of 170 to 190 would indicate a compression ratio of well over 11 to 1. Unless the engine is modified to raise the compression ratio to very high, I would expect to find a lot of carbon build up in the combustion chambers which is causing the high readings. Or possibly an inaccurate gage.
D

[ 09-13-2003: Message edited by: Dave Russell ]</p>