• The Roadster Factory Recovery Fund - Friends, as you may have heard, The Roadster Factory, a respected British Car Parts business in PA, suffered a total loss in a fire on Christmas Day. Read about it, discuss or ask questions >> HERE. The Triumph Register of America is sponsoring a fund raiser to help TRF get back on their feet. If you can help, vist >> their GoFundMe page.
  • Hey there Guest!
    If you enjoy BCF and find our forum a useful resource, if you appreciate not having ads pop up all over the place and you want to ensure we can stay online - Please consider supporting with an "optional" low-cost annual subscription.
    **Upgrade Now**
    (PS: Subscribers don't see this UGLY banner)
Tips
Tips

TR6 TR6 compression test

Terry_M

Senior Member
Country flag
Offline
Just completed a compression test, on a warm engine highest 105--lowest 105--Wondering is this acceptable I have low oil pressure at hot idle (2 lb) and thought refreshing the bottom would extend the life
opinions ,please
Terry
 

TR3driver

Great Pumpkin - R.I.P
Offline
Those readings are a little too good; makes me wonder if the gauge is broken. Easy test, squirt a small amount of oil (like one pump of the can) into a cylinder and check again. I've never had an engine that didn't show at least a 1 psi variation between cylinders, even right after a rebuild. With the oil, the reading should come up at least a little. If it comes up a lot, then the rings are bad.

You didn't give any history; but if the low oil pressure is due to worn bearings in the lower end, then new bearings would certainly pull it up. OTOH if you have a broken oil pump or a big leak somewhere (like maybe something caught in the pressure relief valve, blocking it partially open), then new bearings won't help much.

How do you even read 2 psi on a TR6 oil gauge? Have you checked the gauge for accuracy?
 
OP
T

Terry_M

Senior Member
Country flag
Offline
My bad--the reading for the compression test were from 90-105 (90,100,100.105.105.105 )--No major oil leaks ,new pressure relieve valve The car has 81000 miles on the odometer and i have not driven for three summers . When starting cold at idle it sits at 50 as the motor runs to temp the oil gauge slides to slightly over zero (why i said 2 LB) revving and it comes up to 40-50 and the idles down to zero plus 1-2
I can't say the oil gauge is accurate ,i do believe it indicates a problem The question is what is a acceptable number for a compression test--- I will try the comp test with oil again this week and get back to you
Terry
 

poolboy

Yoda
Country flag
Online
Does the engine smoke when you accelerate /
How many miles can you go before you find you are a quart low ?
 
OP
T

Terry_M

Senior Member
Country flag
Offline
hello
as i said the car has been resting for three summers, can't remember how far until a oil top up ,i get white smoke from the tail pipe on revving I rebuilt the carbs and the final adjustments are proving to be challenging ( i am now far too rich) The oil is 20-50 fresh change
terry
 

poolboy

Yoda
Country flag
Online
It's possible that the piston rings are just stuck around the pistons, having sat so long without movement.
 
OP
T

Terry_M

Senior Member
Country flag
Offline
I thought the car sitting would affect the comp test ,but it shouldn't effect the oil pressure should it ?- To put the car on the road is insurance and licence tags then find out i am running the risk of damaging the motor
 
OP
T

Terry_M

Senior Member
Country flag
Offline
I did the comp test to determine if it was cost effective to freshen the bottom of the engine,which i believe i can complete myself--Low compression in my mind is motor rebuild,which is beyond me and require a professional
Terry
 

Zip960

Freshman Member
Offline
I bought a 1971 rust bucket parts car for the A overdrive and did a compression test on the "warm" engine before removal and the numbers were: 140, 135, 132, 130, 130, 140. It was a CF engine.

All are within 10%. So the engine is GOOD! Almost all maintenance books I have read tell you not to concentrate on the numbers, to just ensure they are all within 10%. That said, I can't understand how you're numbers can be that low. If it was me, I would borrow a gauge and do the test again.

HOWEVER, And after reading the rest of your comments....white smoke, almost non existent oil pressure, 20-50 oil...sounds like a "tired" engine :( Can't rebuild, find a used one on CL and make sure you see it run before you buy!

CHEERS
 
OP
T

Terry_M

Senior Member
Country flag
Offline
hello Zip
i do appreciate the reply with some help other than ,whatever I was looking for other sites for help-- I thought the motor was tired ,was prepared to rebuild freshen the bottom ,the compression was a worry Purchased a new gauge and will try again As i said i rebuilt the carbs and still trying to get the mixture down to acceptable levels .August i plan on reinsuring and driving for a month or so and try the compression again
regards
terry
 

TR3driver

Great Pumpkin - R.I.P
Offline
My bad--the reading for the compression test were from 90-105 (90,100,100.105.105.105 )
Ok, that's still reasonably good. The lowest is only about 10% below the average. No doubt you're losing some power, wouldn't want to go racing with that motor, but it should run fine for the street. I've certainly driven much worse.

When starting cold at idle it sits at 50 as the motor runs to temp the oil gauge slides to slightly over zero (why i said 2 LB) revving and it comes up to 40-50 and the idles down to zero plus 1-2
I can't say the oil gauge is accurate ,i do believe it indicates a problem
Well, the old rule of thumb for minimum oil pressure is 10 psi per 1000 rpm. Since you're looking at a 40 year old version of a gauge that wasn't all that accurate new, it could easily be the gauge off by that much. But I'll agree, it could probably use some new bearings, and check the oil pump while you're in there.
The question is what is a acceptable number for a compression test
The absolute numbers are not really important, since they are affected by all sorts of things including compression ratio, temperature, even humidity and altitude. What you want to look at is the variation between the numbers. +/- 10 percent is considered about the limit for a "healthy" engine; but they will usually still run well enough at +/- 20 percent (although idle may be a little rough). When I got my previous TR3A, one cylinder was down around 85 while the other 3 were around 130! I drove it that way for about 6 months, until I had time & money enough to stuff a set of rings in it. (Then another 2 years before I put in the set of liners & pistons that it really needed.)

If the low compression is from leaking valves, then continuing to drive it may do some damage to the leaking valve seat, possibly pushing it from repairable to needing replacement. But even replacing a valve seat is fairly cheap compared to the overall cost of an overhaul. And if it's just rings that are leaking, they aren't likely to do any more damage than you already have.

That said, changing the rings and lapping the valves isn't that hard for a "shade tree" mechanic, nor does it require a lot of special tools. (It does require some, just not a whole lot.) And it can be done with the engine in the car (so you don't need a hoist, place to store it, etc.) If you just want to squeeze a few years use out before doing a proper overhaul, you might consider rings along with bearings. In my case, one of the rings was actually broken in the cylinder with low compression, so new rings helped a lot even though the cylinder wall was in such bad shape. The rings had apparently rusted to the cylinder during storage (before I got it), leaving a row of rust pits around the cylinder. The bore was visibly oversize through the section with the pits, plus some of the pits were still there. I put probably 30,000 miles on it that way (drove it to work almost every day and all over the place on weekends).

PS, never did get around to doing a proper overhaul on that engine. The OD had quit and I bought another TR3 just to get the OD out of it. Its engine ran better, so I swapped the engine along with the OD. Never heard back from the guy who bought the TR3 with my old 3A engine in it, but he seemed anxious to buy even after I explained what had happened, so I guess he was happy.
 
Similar threads
Thread starter Title Forum Replies Date
P TR6 1971 TR6 compression Triumph 2
T TR6 TR6 fuel line / mechanical fuel pump compression? Triumph 5
E TR6 TR6 Compression Triumph 12
hondo402000 TR6 TR6 Compression readings Triumph 7
Slider748 TR6 '74 TR6 Compression readings Triumph 2
R TR6 Crazy Ignition Failure in TR6 engine… Triumph 7
mctriumph For Sale 69 Tr6 Triumph Classifieds 0
B TR6 TR6 block decking Triumph 2
A TR6 How many fuel filters-TR6 Triumph 20
Got_All_4 General Tech TR6 Transmission Troubles Pops Out of 3rd gear Triumph 2
J TR6 Repadding TR6 frame Triumph 0
S Wanted Need an HVDA conversion kit for 73 TR6 Triumph Classifieds 3
M TR6 Sorting out new TR6 Triumph 10
tr6nitjulius For Sale TR6 Clutch Master Cylinder $40 Triumph Classifieds 0
S TR6 '72 TR6 distributor issues Triumph 3
R TR6 Limit Mechanical Advance on TR6 distributor? Triumph 8
RonC General TR TR3 Shifter on TR6 Triumph 8
B TR6 TR6 convertible top frame Triumph 0
K TR2/3/3A The TR6 gearbox Ist gear.... Triumph 1
tr6nitjulius For Sale TR6 tail light assemby & Resurfaced/New Ring Gear Flywheel Triumph Classifieds 0
tr6nitjulius TR6 TRIUMPH TR6 Triumph 7
S TR6 New tr6 purchase Triumph 31
Jim_Stevens TR6 Barn find of TR6 and many TR3 parts Triumph 9
nichola TR6 Hot spot on cylinder head - 1973 TR6 Triumph 2
R TR6 Heater control bezels TR6 Triumph 2
L For Sale 1974 Tr6 for sale Triumph Classifieds 0
tr6nitjulius TR6 TR6 Parts Visualization Triumph 0
Got_All_4 For Sale 1969 TR6 Driver Seat Triumph Classifieds 0
R TR6 TR6 Choke Cable Triumph 11
Got_All_4 For Sale TR6 TR250 TR4 parts for sale Triumph Classifieds 2
B For Sale TR6 Carburetors Triumph Classifieds 0
R TR6 TR6 Triumph 6
Chrisc9 TR6 TR6 brake light Triumph 6
glemon TR5/TR250 Answering My Own Question Rear Tube Shock Conversion Numbers TR4a-TR6 Triumph 0
tr6nitjulius General TR TRIUMPH TR6 the possibilities! Triumph 12
SherpaPilot TR6 Unidentified fitting on TR6 Engine Triumph 3
Got_All_4 TR6 Need 1969 TR6 Expert Got Questions Triumph 17
tr6nitjulius General TR 6/24/23 TRIUMPH TR6 (5) TR8 (2) Spitfire (1 RHD of 2) TR3A (1) Triumph 0
AngliaGT ANOTHER TR6,& an MGB Spotted 0
A For Sale 1974 TR6 Triumph Classifieds 1
Got_All_4 TR6 Triumph TR6 PDWA Brake Question Triumph 1
EWD For Sale ‘74 TR6 original wheel trim rings Triumph Classifieds 3
EWD For Sale ‘74 TR6 original radio Triumph Classifieds 0
EWD For Sale ‘74 TR6 original starter Triumph Classifieds 0
EWD For Sale ‘74 TR6 original steering wheel Triumph Classifieds 0
JPSmit TR6 at lunch today Spotted 0
E Wanted looking for a tr6 bell housing Triumph Classifieds 12
jfarris For Sale TR6 Yellow Fan - new Triumph Classifieds 0
L Wanted right front turn signal 1975 TR6 Triumph Classifieds 2
charlie74 ‘74 1/2+ TR6 Spotted 0

Similar threads

Top