Cylinder compression

[Graze]

gents

 

I have never personally tested the compression on my TR6

 

it has done 220,000km and as far as I know hasnt had a rebuild - certainly not in the past 120,000km (as PO owned it for 15 years & I've had it back for 2 & a bit years)

 

when the dyno shop checked it today to tune the new throttle bodies they tested the compression and got 200 across all 6 cylinders - they tell me they checked it twice as they couldnt believe it

 

has anyone had similar readings - i was expecting 150-160 range

 

or even lower given engine age

 

I'd be interested in your experiences

 

Graze

[Motorsport Mickey]

Hi Graze,

 

Not on the same subject but was this the dyno shop who provided the power and torque sheets on the 4 cylinder which didn't cross at 5252 revs ? and if so could they explain why they didn't ? Not criticising just perplexed why I can't work out the sheets.

 

Mick Richards

[oldtuckunder]

 

when the dyno shop checked it today to tune the new throttle bodies they tested the compression and got 200 across all 6 cylinders - they tell me they checked it twice as they couldnt believe it

 

has anyone had similar readings - i was expecting 150-160 range

 

or even lower given engine age

 

 

Well I kind of hope that they were 196,192, 202,198,208,200 or some random patterm around 200, or I justy wouldn't believe what they told you. Virtually no compression guages are calibrated so one persons 180 is anothers 200, but the important thing is that they are all dam close and not low. Exactly how high isn't as important.

 

Did they tell you when/how they tested cold, warm, hot, wet, dry? but regardless a nice set of numbers, that some people with fresh rebuild engines would be envious of.

 

Alan

[Nick Jones]

My old 2.5 PI engine produced numbers between 190 and 200 across all 6, tested hot with the throttle wide open.

 

This was a particular surprise as I already knew it suffered epic blow-by and drank oil a like a rabbit hole and I was certainly expecting some low numbers. Our working hypothesis was that there was so much oil around the compression rings, every test was a "wet test"! Certainly a wet test didn't make alot of difference. The new engine actually produced slightly higher numbers (between 200 and 210) as the head was skimmed a little to raise the compression.

 

Having said that, a full set of even compressions on an engine that runs well, doesn't blow oil our of every seal and joint, chuff like an old steam train out of the breather or burn oil, can be considered a positive sign whatever the mileage.

 

These engines can be very long lived if properly maintained (and not thrashed mercilessly all the time) so I certainly wouldn't take mileage alone as a signal for rebuild. They also tend to die slowly so (dropped thrust washers aside) it's rare to be suddenly forced into a rebuild.

 

Nick

[Graze]

Hi Graze,

 

Not on the same subject but was this the dyno shop who provided the power and torque sheets on the 4 cylinder which didn't cross at 5252 revs ? and if so could they explain why they didn't ? Not criticising just perplexed why I can't work out the sheets.

 

Mick Richards

Mick I did ask them about that, he said torque on a chassis Dyno is affected by a range of things including gearing, tyre size (my car has small tyres -205/50/15 which mean it is about 25% out on original size tyres), Dyno and that it isn't just a theoretical calculation.

 

All above my pay grade I'm afraid - can say the TR4 is brilliant to drivevandchas loads of torque from 2500 rpm up

 

Graze

[stallie]

Resurrecting an old thread...

 

I mesured my compression tonight after taking it for its first run after too many years off the road.

 

Between 204 and 210 across all six. I didn't have the throttle open (have only just realised that it's suggested).

 

I christened my unused still-in-box 1974 Penske flexible drive compression tester bought from Sears and given to me by my old neighbour many years ago. After much head scratching I discovered that the reading on the outer scale was in lbs per sq cm! But 200 lbs/sq/cm made even less sense when realising that 200 PSI is on the high side (CP). Much googling later I have discovered that it's actually a misprint - it should be PSI. I guess I can't take it back, although the receipt is in the box....