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Bob Legate
06-27-2014, 12:46 AM
1971 TR6, does anyone know what the compression readings should be? Mine range from 110 to 120. Trying to decide if I need to rebuild the motor. It runs great, pulls hard and doesn't smoke. Thx for your help. Bob

TOC
06-27-2014, 01:15 AM
I'll share one thing...and not the spec. Turn your compression gauge over. Do you see a current calibration sticker from a top laboratory?
Maybe it fell off, right?
I ain't never seen one calibrated.
You can try a half dozen gauges and get a half dozen readings.
What you look for is consistency. Rule of thumb is plus or minus 10%
110 is 11, added is 121, so you're okay.
Do a wet next.
Squirt of oil down each hole, spin it a couple of times, and do the readings again.
Worn rings will give you a big bump up in readings. If it stays reasonably close, rings are fine.
You can do a leakdown if you suspect something.
Not a lot of oil..knew a guy who did that once..his readings were scary...all the oil filled the combustion chamber.
Dave

TR3driver
06-27-2014, 02:12 AM
Right. Only the comparison between readings is important, not the actual values. Your numbers are within +/- 5%, which is quite good.

With readings like that dry, I don't see any sense in doing a 'wet' test unless you can precisely control how much oil is in each "squirt". The oil will always increase the reading a little, and somewhat proportional to the amount of oil used; so any variation in the amount of oil will cloud the results. Besides, it doesn't matter if you aren't going to tear the engine down.

toysrrus
06-27-2014, 02:30 AM
Hi Bob,

There`s an old saying in the Classic Car World especially LBC`s.

"IF ITS NOTS BROKEN, DON`T FIX IT"!!

Your compression readings & running cond. don`t call for anything except "Drive it like you stole it"!!

Happy Motoring,

Russ
1971 TR6, does anyone know what the compression readings should be? Mine range from 110 to 120. Trying to decide if I need to rebuild the motor. It runs great, pulls hard and doesn't smoke. Thx for your help. Bob

glemon
06-27-2014, 03:59 AM
I agree with Russ, focus on the "it runs great, pulls hard, and doesn't smoke part" I have had cars with compression reading well out of the normal range that have run fine for years, I think my old Austin Healey had a couple cylinders that struggled to hit 90 lbs on a couple cylinders, and it still pulled like a truck. I did eventually rebuild it, but it was also smoking a bit, and still drove it many years before the rebuild.

TOC
06-27-2014, 11:48 AM
Right. Only the comparison between readings is important, not the actual values. Your numbers are within +/- 5%, which is quite good.

With readings like that dry, I don't see any sense in doing a 'wet' test unless you can precisely control how much oil is in each "squirt". The oil will always increase the reading a little, and somewhat proportional to the amount of oil used; so any variation in the amount of oil will cloud the results. Besides, it doesn't matter if you aren't going to tear the engine down.

The "little" is what you want to see. Since no one knows what their gauge calibration is, if a customer is showing concern, always best to do a wet and dry to insure.
Pump oiler (small), been using the same one for 25 years...prime, then one squeeze per hole.
Spread it around the upper rings a bit by spinning....temporarily provides better ring to wall seal.
If you've done this often enough, you can see when the rings are starting to go.
Maybe I've just done so many, all kinds of cars, I know what I'm looking for and at.