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Triumph TR6 - compression

I am going to do a compression test and I was wondering what is normal(good) compression.My car has 75,000 miles,runs well but smokes a little after idling for a while and when I start it up after driving.I can't afford a rebuild right now,but would a valve job be benificial or a waste of $$?I only drive it about a 1,000 miles per year.Thanks for any input,Erik '72 tr-6
Erik Helland

Usually smoke on start up after sitting overnight means warn valve guides as the oil seeps down and contaminates the cylinder. My car smokes like an old oil furnace when I start the car up cold (talk about stinky, my neighbours love me!) . Once the oil is burned off (1-2 minutes) I get no further smoke and subsequently only use a little more than normal amount of oil.

If you get blue smoke when decelerating it usually means warn out rings.

I would be interested in hearing what kind of compression you guys are getting out of an unmodified low-compression ratio engine (i.e. '73, 7.5:1). I will also be doing another compression test on my '73 in addition to doing a cylinder leak-down test (I just purchased the leak-down tester from Eastwood). My previous compression tests were lower than I would have liked (110 to 120 psi). The leak-down tester is supposed to identify if it is bad valves or rings. I haven't yet spent the time to calculate what the ideal compression psi should be for the low-compression motor.

Actually, now that you got me started...

if atmospheric air pressure is approx 15 psi, then 15 psi x 7.5:1 ratio = 112.5 psi (plus 15 psi due to initial gauge reading of zero = 127.5), providing temperature is held constant (P = V * t).

Anybody agree? or is this off?

That's how I would calculate it. The compession tester will give 'gauge' readings rather than absolute pressure, so a reading of 100-110 for a 7.5 head is correct. I look for agreement between readings rather than the actual values, so even if your readings spanned , say, 95 to 105, with none excessively low ( eg 85 ) then all is well.
If one cylinder is low, a useful trick to test for bore wear is to put a 5-10 ml of engine oil in the bore and retest. If the reading is higher its a bore/ring problem (or possibly a cracked piston), if not its a valve.
Peter Cobbold

Well, that's good to know that my compression is not so low. The car has been idle for several years, so I recently restarted it. I used a transparent line to the intake side of the fuel pump, and put the other end in a small container of clean gas on the floor. The fuel pump sucked the gas up into the motor and the thing started. No exhaust smoke, but I was concerned about the compression. The carbs will need to be cleaned and re-adjusted. I've drained the tank - the gas that was still in there was nasty.

I had recently been given some advice from this site on how to pick up the body, and within a month the body should be off. I've waited many years to restore this car - eager to get it apart and back together. The interior is now out (trashed) and after some more diagnostics, I'll remove the dash, windshield, and remove the body.

I noticed that my oil pressure was not indicating on the gauge - I've bought a cheap one to check it before buying a Smith's gauge. Prior to starting it, I let it crank without spark and observed oil flowing around the rockers. There is no knocking from the rods, so hopefully my bottom end is ok. The car has about 78K original miles on it. Wire wheels, no OD. Still has the factory radio. In fact, the rear shocks are still coated with undercoating, so the car is almost original - just needs new paint, interior, and mechanical improvements.

Anyway, I'll keep y'all advised and continue to ask questions as they come along.


Well I finally got around to doing that compression test,here we go,#1/100 dry 130 wet #2/90 dry 110 wet #3/90 dry 110 wet #4/80 dry 105 wet #5/90 dry 110 wet #6/95 dry 120 wet What does it all indicate? I have 40 lbs oil pressure hot at idle and 65 lbs while driving.I know she's a little tired,but I am going to baby her along for at least another season,it doesn't smoke,only when I start up(mostly when warm)and after idling for long periods.Thanks for any input,love this site!Erik '72 tr-6 74,000 mi.
Erik Helland

Hi Erik

Your readings are exactly that a little tired. But all in a range. So your motor should tick along. Just over all wear.

Don't know what criterion you used and or equipment.

If you used engine well warmed 10 minute run not idle. All plugs out 4 compression spins aprox. for each cylinder with a good quality screw in type compression gauge you are quite low. But all within a reasonable range. The difference between wet and dry tell rings or valves. Over 150 using the above criterion is nice. I doubt if you warmed up the engine by your readings?

Bill Brayford

The engine was cold and I used a screw in type of tester,Craftsman,the car does run really quite well hardly burns any oil,sounds pretty tight,but is a little slow.It looks real nice,and I get alot of compliments,it has all accesories(overdrive,hardtop,chrome wires, redlines etc.)and everything works.Thanks for your reply,Erik
Erik Helland

Try advancing the timing more with the distributor. I found what seemed like a lot more power by advancing the distributor a few degrees at a time and test driving after each advance. When it stopped making more power I quit advancing. It never did ping at any of the advancements. I ended up with at least 10-15 degrees at idle. It made a big difference. My buddy scatched tires with it in 2nd gear. Stock '74 engine with 108,000 miles on it. 205 wide goodyears.
Steve H

We TR owners who have had our cars for some time have learned to apply the old adage, "If it ain't broke, don't fix it". It sounds to me that your TR6 can run fine for a summer or two more before you need to change the rings.

I suggest that you check with other members in your area

Rocky Mountain Triumph Club
6821 S. Forest St., Littleton, CO 80122
Glenn Sorensen, VTR Liaison,, 303-220-9742

to find out what their compression is. Those who have answered you above have not considered that you live between 5,000 to 12,000 foot altitude and it's normal that your readings will be lower than we down here at sea level. Say hello to Glenn from me.

When I drove my TR to Breckonridge for VTR two summers ago, I drove over Estes Pass at 12,095 ft. altitude. I had to lean out my carbs about 2 flats in Loveland (5,000 ft) before going any higher.

Enjoy your TR and drive it.

Don Elliott, Original Owner, 1958 TR3A
Don Elliott

I agree with Bill and Don- leave well alone and enjoy driving it. I found that when the bores got worn the oil pressure fell from around 50 at 2500rpm to 25-30 after a climb at 70 mph up a long hill. The blow-by past the pistons probably heated the oil and the pressure dropped. You wont get a catastrophoic failure from a bit of wear, unless you're racing.
P H Cobbold

I know pretty much the whole history of my tr from when it was bought from the dealer.I am the third owner.It belonged to a very dear friend of mine,he was the best man in my wedding using wedding cars sevenoaks 18 yrs ago.He passed away 10 yrs ago and he loved the car.We all had british cars in high school,probably ten of us,triumphs,mgs,jags,a sprite, my dad even had a cortina.Anyway his mom moved to Oklahoma,took the car and stored it.She said she drove it in a parade and that was about it.She moved back here and was forced to sell it due to health issues,advertised it and I happened to see it in the paper.Talk about fate,I bought it did some work on the car went back to visit a few more times with the tr.She was so happy I ended up with it.Sadly to say that she passed last July.I hope that I will never have to part with it.Love driving it,lots of memories.p.s.I also drove it to Breck.what a fun time!Mine is dove grey with a red 250 stripe on the hood.Sorry for rambling on,Erik
Erik Helland

Hey Erik

Never apologise for rambling on and you weren't great info. If as a group we didn't love nostalgia we would be comparing lease rates on Hondas. Now that would be rambling.

Thanks Don never did notice Denver till you pointed it out. That will definately lower your readings as well.

Considering cold test and atmosphere you seem OK.

On that same note if the car was tuned for Oklahoma? Contact Dons friends and check out there setup for your area. Might be all you need to perk it up.


Bill Brayford

Tuning for high altitude? There's no better way than supercharging. See if you can find one of the Eaton- based kits that Vintage Induction Systems made a few years back, it bolts onto the stock engine.
P H Cobbold

This thread was discussed between 03/01/2003 and 21/01/2003

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