• Hey Guest!
    British Car Forum has been supporting enthusiasts for over 25 years by providing a great place to share our love for British cars. You can support our efforts by upgrading your membership for less than the dues of most car clubs. There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Upgraded members don't see this banner, nor will you see the Google ads that appear on the site.)
Tips
Tips

Compression check

Share this page

prb51

prb51

Luke Skywalker
Country flag
Offline
I've got the 3 waiting for it's refurbished header so the carbs/intake are off along with the old header and was thinking this would be a good time to do a compression check as I've got automatic WOT the way she sits.
Any problem with my thinking and what psi should I be looking for anyway?
 
prb51 said:
Any problem with my thinking and what psi should I be looking for anyway?
Click to expand...
It's more important that the reading be (nearly) constant across all cylinders. Many things not having to do with engine condition can affect the exact value shown. Normally, all values within 5% +- of the average is considered good, and 10% is acceptable (unless you're going racing).
 
TR3driver said:
It's more important that the reading be (nearly) constant across all cylinders. Many things not having to do with engine condition can affect the exact value shown.
Click to expand...

+1

You've obviously going to be testing your engine cold, since the whole intake is off. That'll probably give you lower compression readings than if the engine were warm. Don't let that scare you. All kinds of things can effect the exact numbers. Engine temperature, ambient temperature, altitude, throttle position, air filter, fuel line disconnected or not, etc. As long as your numbers are consistent and not ridiculously low, you're engine has 'passed' the compression test.

One thing I've learned: I've gotten numbers on a compression test before that were very scary, but turned out to be the result of valve misadjustment. Fixing the valves brought the numbers in line. So now I don't bother to do a compression test on an unknown engine until after I've done a valve adjustment.
 
And, of course, you'll want all the spark plugs removed for the test, not just one at a time.

I also clamp the fuel line so it's not pumping fuel while cranking.
 
Thanks, good advice all.
Geo, I still have the fuel shut off petcock that works and I'll empty the fuel bowl and put the line in a container for safeties sake.
Actually, just looking for something 'car' to do while I wait for parts.
I've polished and painted everything I can think of in the engine bay and ended up oiling the leather seats and putting protectant on all of the rubber hoses/grommets...oh yea, and took a .22 cal wire brush to all of the open bullet connectors.
Waxed everything the apron covers (to include the aprons underside)....
Tightened this/that....
Checked the toe in.....
My wife thinks I've lost it.
 
I was fortunate to find 110-115 in each cylinder. You have definitely not lost it - you're just finding it.

Say - how 'bout some pictures of all that engine bay work?

Tom
 
On the late TR3A I restored, the owner had not run the engine for the four years it sat in his garden under a tarp - after it was plowed sideways along the highway by the front bumper of a Freightliner. He told me the engine had been re-built and improved just before the collision. During the seven years I had it for the restoration, I checked the compression (cold) several times. The readings were scary ! 100, 20, 20 and 50. The owner told me not to do anything to the engine. When it was all finished and ready to run, it warmed up nicely and I re-checked the compression while it was still hot. I had the throttles (butterflys) fully open and had removed all 4 sparkplugs. The readings were 170,170, 165 and 165.
 

Attachments

  • 8517.jpg
    8517.jpg
    43.1 KB · Views: 85
Don,
Wonder what I'll get cold but as you say, I'll not worry about it as she goes nicely.
Are these two dif cars or pre repaint? I suspect they are two and do you still have both?
I've heard similar stories about 3 motors standing neglected and firing right up once tuned, good little motor.
Here are some pics but the clean up etc was unintentional. I originally was just changing the rad out but found a small hole in the header ergo....
https://i216.photobucket.com/albums/cc138/prb51/MomvisitCars055.jpg
https://i216.photobucket.com/albums/cc138/prb51/MomvisitCars054.jpg
https://i216.photobucket.com/albums/cc138/prb51/MomvisitCars056.jpg
https://i216.photobucket.com/albums/cc138/prb51/MomvisitCars057.jpg
 
My own TR is a black 1958 early TR3A. I bought it brand new 49 and a half years ago. The green one is a late TR3A that I did for the owner who lives in Toronto. Attached is a photo of me with my car taken at VTR in Colorado in 2001.
 

Attachments

  • 8519.jpg
    8519.jpg
    148.9 KB · Views: 120
Don,
Both cars look great.
There is something special about owning a car that long, like a marriage, no secrets.
I've sold too many I should of kept: the 1962 Maserati 3500 GTI I bought in Italy as a young Sergeant (and drove there for 3 years) and the E type Jag I picked up after RVN.
I admire guys that buy and keep for years.
 
The photo of your engine compartment shows stop bolts for the clutch & brake pedal returns. Do someone know -- was this originally done? Was in continued with TR3As?

My bracket has the holes for this and it seems this might be a useful adjustment to take up some of the inevitable slop that develops as the parts wear (esp the hole in the top end of the pedal arm that gets ovalled by the clevis pin.

Brake%20Stop%20Bolt.JPG
 
Early cars had the stop bolts, but they were discontinued at some point. I think during the TR3A run, but I'm not sure offhand.

A drop of oil once in awhile will help keep those holes from wearing ...
 
My TR3A (TS 27489 LO) didn't have any stop bolts when I bought it in May, 1958. The holes are there in case I ever wanted to add them. But I've seen them on later cars. These might have been added by recent owners.
 
My TR3 TS14502L had the stop bolts on as I have pics of the original car as it was taken down and redone by the PO ( a great home frame off ).
When I purchased the vehicle the PO (deceased, bought from 3rd party) had collected all of the registration/maint documents (hard copy originals) going back to 1972.
It was basically unmolested when the resto was done from mid to late 90's and looked it, it hadn't been driven since 90 but was in limited service up to that point (very ratty).
The PO had earlier photos of the car and did a nice job of cataloging all of his work with pics and kept every receipt and bit of info related to the car.
When I read about Pedro and other DPO's I thank Mr. P for all of his hard quality work and wish I could have met the gentleman. I'm sure he would have enjoyed this site.
 
Back
Top