One for engine gurus

[Ecosse]

At my final Hillclimb of the year at Doune in September in m 7, over the course of the weekend what started off as a puff of blue smoke ended up as a smoke screen that the Royal Navy would have been proud of. A constant stream of spectators visited me in the paddock to advise of the issue, as did some event officials. It was definitely oil smoke from the exhaust pipe, but there was no apparent loss of performance.

A compression test provided the following results, No.1 - 160 psi, No.2 - 170 psi, No.3 - 155 psi, No,4 - 170 psi.

With 4-squirts of oil directly in to each cylinder readings were, No.1 - 170psi, No.2 - 190psi, No.3 - 160psi, No.4 - 190 psi.

Immediate thoughts were a ring issue, particularly on No.3, but with the head off the bores appear to be perfect. I would have thought that there may be some visible signs on the bores if the rings have broken, or whatever. I am currently checking valve sealing on the seats, but that also appears to be OK. I am looking for any possible causes of the issue prior to taking out the engine and stripping it down.

Does anyone know if there are issues with head gaskets allowing oil from the oilways to get into the cylinders, or perhaps valve guide/stem issues allowing oil into the cylinders. The engine was painstakingly completely rebuilt last year.

Any thoughts would be gratefully received.

Cliff

[BlueTR3A-5EKT]

Not something silly like servo seal gone?   Check the brake fluid level

[trchris]

It’s a shame you’ve removed the head as a leak test might have helped, have you tried filling the bores with thin oil and seeing if any leak ? 
Chris

[john.r.davies]

Cliff,

"A compression test provided the following results, No.1 - 160 psi, No.2 - 170 psi, No.3 - 155 psi, No,4 - 170 psi.

With 4-squirts of oil directly in to each cylinder readings were, No.1 - 170psi, No.2 - 190psi, No.3 - 160psi, No.4 - 190 psi."

I note that the 'wet' readings were all 10-20psi above the dry series, except for No.3, which only rose 5psi.    Adding a little oil is a test for valve failure, as it will improve piston ring seal, but not that of the valves.   I'm less clear as to how a failed valve seal should have caused a Jutland quality smokescreen!    But worth special attention IMHO.

John

[iain]

1 hour ago, BlueTR3A-5EKT said:

Not something silly like servo seal gone?   Check the brake fluid level

My thought too.

[Hamish]

Cliff 

have you used oil or coolant ?

does it happen regardless of engine temp ?

are you sure it’s oil burning ?

good ideas around the brake system  

despite good compression you can still have oil rings or others going. 
 

I had good compression but a broken ring landing. No bore scoring either. 
happened twice about 100 miles apart on my 3a

Edited December 8, 2025 by Hamish

[BlueTR3A-5EKT]

1 hour ago, Hamish said:

Cliff 

have you used oil or coolant ?

does it happen regardless of engine temp ?

are you sure it’s oil burning ?

good ideas around the brake system  

despite good compression you can still have oil rings or others going. 
 

I had good compression but a broken ring landing. No bore scoring either. 
happened twice about 100 miles apart on my 3a

That was going to be the next suggestion. 

Piston ring lands failed.

 

A set of forged pistons might be the cheaper solution to pulling the engine frequently and buying replacement single pisons.  The day the liner goes west may also push your pocket and humour.

[BlueTR3A-5EKT]

9 minutes ago, BlueTR3A-5EKT said:

That was going to be the next suggestion. 

Piston ring lands failed.

 

A set of forged pistons might be the cheaper solution to pulling the engine frequently and buying replacement single pistons.  The day the liner goes west may also push your pocket and humour.

 

[Ecosse]

Thanks to all for your thoughts, and I sometimes marvel at my own ineptitude.

After thoroughly cleaning the pistons crowns of light carbon deposits and oil from the compression check I have discovered cracks on the crowns of Nos. 1 and 4, so I guess that is the issue. The next issue is what caused the damage, I have two front runners. Perhaps 'Standard' spec pistons are not up to the rigors of competition, I investigated forged pistons, the cost seemed disproportionate but I guess I may have to bite the bullet. The other possibility may be mechanical in that the block was skimmed just enough to clean up the mating face, which resulted in a slight protrusion the pistons by differing amounts of up to five thou maximum, Nos. 2 and 3 having the greatest protrusions, obviously there are some manufacturing tolerances in the pistons. I was assured by my machine man, who also builds competition engines, that this would not be an issue, perhaps I should have had the pistons machined.

The staggering thing is that the car ran well, if a tad smokey, despite the issues.

Anyway, the engine has to come out and be rebuilt.

Hindsight is a marvelous thing, thanks again to all for your comments.

Regards,

Cliff

[BlueTR3A-5EKT]

Oh where are they now…

TR7 short engines.  New factory Block, crank rods and pistons that cox and Buckles/Moss had, and we struggled to sell at £75.00 each.

pt nos RTC2549 or RTC1286 or RTC229   Can’t remember the sprint part number.

Tony Dean was or biggest customer for them and the Sprint version.  He had at least one a week as swaps for rebuilt gearboxes and diffs.

Sprint spares had a large stock of bare blocks too.

Edited December 8, 2025 by BlueTR3A-5EKT

[harrytr5]

When building my Dolly sprint I bought one of those short blocks from Jamie of Sprint Spares many years ago and he had Nigel Mansell's sprint engine F1 car in his premise near Southend. Went there a few times. Must have seen a dozen short blocks in their crates. Happy days.

Tony rebuilt my head.

Regards Harry

[Ecosse]

Does anyone have an experience of JP Pistons as supplied by FW Thornton which are cast and noted as equivalent to AE/Hepolite pistons. The cost is approximately double that of the County pistons supplied by all the Triumph parts suppliers.

Forged pistons are only available to special order and are roughly five times the cost of the County offerings, so it is a cost/benefit exercise.

Thanks for any information.

Cliff

[BlueTR3A-5EKT]

21 minutes ago, Ecosse said:

Does anyone have an experience of JP Pistons as supplied by FW Thornton which are cast and noted as equivalent to AE/Hepolite pistons. The cost is approximately double that of the County pistons supplied by all the Triumph parts suppliers.

Forged pistons are only available to special order and are roughly five times the cost of the County offerings, so it is a cost/benefit exercise.

Thanks for any information.

Cliff

I have not heard anything negative about the JP Piston product

As they are Australian perhaps some feed back from there might be helpful

https://www.norndaautomotive.com.au/our-brands-jp-pistons.html

https://www.norndaautomotive.com.au/jp-pistons/find-parts/jppistonsproducts.html?make=Triumph&model=TR7 (European Version)

Further reading on the now closed Venolia brand forged pistons for TR7.

https://www.triumphexp.com/forum/tr7-and-tr8-forum.3/tr7-high-compression-pistons-200.1433703/

If you resleeve the block…..Fitchett has standard sized originals   https://www.ebay.co.uk/itm/115141145572?var=0&_ul=GB&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5339022012&toolid=10029&customid=364973558759626899&loc_interest_ms=&loc_physical_ms=40990&gclid=a9f86b5b2f5517bb02940261f7e19d36
 

 

 

 

 

Edited December 11, 2025 by BlueTR3A-5EKT

[Andy Moltu]

On 12/10/2025 at 9:12 AM, harrytr5 said:

When building my Dolly sprint I bought one of those short blocks from Jamie of Sprint Spares many years ago and he had Nigel Mansell's sprint engine F1 car in his premise near Southend. Went there a few times. Must have seen a dozen short blocks in their crates. Happy days.

Tony rebuilt my head.

Regards Harry

Do you mean F3? 

The hotted up Dolly Sprint engines performed remarkably well but we're a few cylinders and 1500cc short of the 3.5l F1 engines of that era. 

Makes you wonder how much better the Stag engine could have been. 32 valves and coolant flow designed better....
Too heavy for F1 but could have been so much better had the money been there.

[harrytr5]

Yes Andy F3. Jamie had both of his (ex Mansell)cars in the foyer area and the first thing you saw when entering  Jamie's  premise.

I fully rebuilt my Dolly Sprint and only did 2000 miles in it and sold it to my mate to fund my rebuild of my then TR6. Alan then drove it for ten years clocking up  thousands of miles,he loved it.

That upright screen was a tad noisy in the wind though.

Happy Days

[Spit_2.5PI]

22 hours ago, Andy Moltu said:

Makes you wonder how much better the Stag engine could have been. 32 valves and coolant flow designed better....

... or a 24 valve 3l Rover SD1 (Triumph) 6-cyl engine with a decent cam?

Cheers, Richard

[acaie]

On 1/24/2026 at 3:05 PM, Andy Moltu said:

Do you mean F3? 

The hotted up Dolly Sprint engines performed remarkably well but we're a few cylinders and 1500cc short of the 3.5l F1 engines of that era. 

Makes you wonder how much better the Stag engine could have been. 32 valves and coolant flow designed better....
Too heavy for F1 but could have been so much better had the money been there.

The Repco V8 with its shared ancestry with the Rover V8 did win a F1 championship. 
There is more than one story about why the Stag did not use the Rover v8 - one being internal BL politics; another being insufficient Rover v8 production capacity. 

 

[john.r.davies]

Ian Taylor in his Dolly-engined F3 March, with Tiff Needell (clock the hair style!)

From Graham Robson's The Works Triumphs

Edited January 27 by john.r.davies

[multipletriumphsinner]

On 1/24/2026 at 3:05 PM, Andy Moltu said:

 

Makes you wonder how much better the Stag engine could have been. 32 valves and coolant flow designed better....

Indeed, its a wonder a standard Stag managed to pump out 145bhp with one of the softest cams in the Triumph range (16/56 56/16), and one of the lowest compression ratios 8.8.

Piper used to do a cam for the Stag, I cannot remember the specifics, but fitting one of those, raising the compression ratio, and a bit of fiddling with the carbs, and timing used to bring an easy 20-30 bhp gain. 

Back in the 70's I used to pop into a school mates Dads welding/machine/fab shop  on the way home from school who did sub contract work for Triumph. My mates Dad was one of the most skilled aluminium welders in the trade, and he often did stuff for the local car factories. One time we went in he was welding some new cam chain boxes on the wrong end of what looked like a modified Dolomite Sprint heads. He mentioned Stag.

Edited January 28 by multipletriumphsinner

[Ecosse]

Going back to the original subject.

I have purchased a set of the JP Pistons which appear to be of better quality than the 'Standard quality' pistons as supplied by all the major parts suppliers. The bores are to be match machined to the new oversize pistons. I found it difficult to justify the cost of forged pistons.

New 'standard quality' bearings and oil pump were fitted on the previous rebuild but the oil pressure was disappointing at 40 to 50 psi depending on revs, I was expecting a bit more op but perhaps 7s run at a lower pressure. Any thoughts regarding preferred bearings and pump suppliers.

All valves have been lapped in again in case that was the issue with compression on No.3 cylinder.

Regarding Stags, when I purchased my Stag it was fitted with a 2.5pi engine which was probably gave better performance and BHP than the V8. It now runs on SUs with a flowed head, 6-branch and uprated cam and goes really well, so much so that I considered a Stag as a Hillclimb car prior to purchasing the 7. I probably should have gone for a Stag as it impressed at the Bo'ness Hillclimb Revival.

Cliff