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TR8 compression test

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TR8 compression test
#1
  This topic is about my 1980 Triumph TR8
BOBSTR4 ROBERT BLAKE
AUSTIN, USA   USA
1980 Triumph TR8 "Ralph"
I would like to perform a compression test on my 80 TR8. Without having someone sitting in the drivers seat to bump the ignition, I have run a lead from the battery plus to a hand held pressure switch and then to the starter positive side. This way I also avoid going through the ignition so the distributor is also offline. Disabled the fuel pump at the fuel tank by disconnecting the hot lead. All plugs removed. Should be good to go, right. What have I missed??

RB

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POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
I think you're good to go. For an accurate reading you should have the throttle open and a means to keep the carb's piston up.

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Secretbuzzard John Greenwood
Jacksonville, FL, USA   USA
1960 Morris Mini-Minor
1974 Triumph TR6 ~ For Sale ! ~
1980 Triumph TR8
You should pull the wires off one side of the coil because the bypass circuit will energize the ignition when you engage the starter solenoid. Otherwise everything sounds right!

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RossL Silver Member Ross LoMonaco
NJ, USA   USA
I like doing a test with the engine warm. Are you planning to run the car for a while before the test?
A cold engine could give misleading results

BOBSTR4 ROBERT BLAKE
AUSTIN, USA   USA
1980 Triumph TR8 "Ralph"
Roger that. Will do both cold and hot

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TeeR8 Gold Member Henri Lefebvre
Calgary, AB, Canada   CAN
Robert,

What type of 'pressure switch' are you using? I might use your technique in the future.



Henri
1980 TR8, Platinum
1971 MGB GT, Midnight Blue

Secretbuzzard Avatar
Secretbuzzard John Greenwood
Jacksonville, FL, USA   USA
1960 Morris Mini-Minor
1974 Triumph TR6 ~ For Sale ! ~
1980 Triumph TR8

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BOBSTR4 ROBERT BLAKE
AUSTIN, USA   USA
1980 Triumph TR8 "Ralph"
Made my own switch for about $3, thanks

BOBSTR4 ROBERT BLAKE
AUSTIN, USA   USA
1980 Triumph TR8 "Ralph"
Will disable the coil. thanks

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BOBSTR4 ROBERT BLAKE
AUSTIN, USA   USA
1980 Triumph TR8 "Ralph"
What would be considered reasonable pressure readings.

Bergie Bob Berg
Powell, OH, USA   USA
disable coil by pulling coil wire...plug in compression lead to each cylinder and crank over so you get at least 3 compression hits per cylinder...should be greater than 175 each cylinder...over 190 if cold...

POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
In reply to # 1522486 by Bergie
..should be greater than 175 each cylinder...over 190 if cold...

Those are super high numbers. These numbers do not represent the average 3.5 engine. Your's may vary. Compression gauges are all over the spectrum of accuracy. My pressures are 145 + or - with one gauge I own and 155 + or - with another one. Important that they are within around 10% of each other no matter what the PSI.

By the way pressures tend to higher when testing a warm engine and lower with a cool one... typo Bergie? - Pete

Bergie Bob Berg
Powell, OH, USA   USA
Pete...I have a 4.6L...tested cold... high compression engine from Woody....

POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
In reply to # 1522557 by Bergie Pete...I have a 4.6L...tested cold... high compression engine from Woody....

Well don't take this the wrong way, I'm still skeptical about those numbers however. CI does not really dictate Compression Ratio. In the Buick derived Rover engine, piston dish or lack of does. Skimming the head can add to that too I guess. I have no idea how "built" your particular engine is but Roberts original question (post # 10) was about "reasonable pressure readings", presumably for a very stock 3.5, so stating "greater than 175 (190 cold)" is a bit misleading.

Oh, and I should mention Robert, that my own engine has been rebuilt with 9.65:1 pistons so my own and I have a different cam as well, So my average between my two gauges of 150 PSI may not be what you see either. As I recall, when the engine was as from the factory with a stock compression ratio of 8.13:1, I got pressures ranging from 137- 143 PSI.



Edited 1 time(s). Last edit at 2018-03-31 03:41 PM by POW.

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