JP pistons

[flying farmer]

I started to clean off my pistons tonight with the intention of fitting the new set of county rings I had bought. Much to my dismay the ring thicknesses on the middle ring are way different, in fact the same as the top ring.

I now realise the engine has been fitted with a set of JP pistons, which are undoubtably incredibly strong as they have made a good job of bending valves and battering foreign objects into the cylinder head without suffering any significant damage. They are also somewhat heavier than the originals. My digital scales have a flat battery, but the kitchen scales say about 70 grams each

I searched the forum and found that Tony Hart will not use them because of the weight, he said 2 kilos a set which may be an over exageration but I am now wondering wether to use the set of new county pistons I have in the cupboard. I think a new battery for the scales, and a dummy build to check deck heights and possible compression ratios is needed

Oh for a simple life:?

Neil

[jusm]

My new JPs are about 200g heavier than standard. Not sure how I'm going to remove 33% of excess material!
How noticeable would the impact be to acceleration of the heavier Pistons if left as they are?

[bullstarz]

It wont make a difference to the performance of your engine, it just means there will be more moving mass. So that would put a strain on the internals. The higher you rev the higher the inertia of those parts.

The pistons in my engine are Wisco, light and a piece of artwork, They looked too good to be hidden in the inside of an engine.

[Stagsongas]

My digital scales have a flat battery, but the kitchen scales say about 70 grams each

Oh for a simple life:?

Neil

Neil,

Slightly less problems if you remember to wipe the black ring off the scale pan before going back to the workshop - I've learned!

Regards

Steve

[Stagsongas]

Bullstarz,

You're right! Sculpture in metal, quite beautiful!

[jusm]

Wow.. they are nice...What did they weigh and how much?

never heard of Wisco. Didn't want County as reports were mixed and I thought JP were the only real alternative. Wishing I had searched harder now ��

[flying farmer]

My new JPs are about 200g heavier than standard. Not sure how I'm going to remove 33% of excess material!
How noticeable would the impact be to acceleration of the heavier Pistons if left as they are?

I have heard some bad things about JP pistons seizing.
Although this post originated in 2011, I found some scoring on no 8 piston when I stripped the engine down.
I assumed it was due to a previous overheating problem and to be fair it hasn't given any more trouble in the last 5 years.

However someone sent me a PM recently enquiring whether I had honed the bores for extra clearance as they had suffered a seizure on the motorway with the JP pistons which basically knackered them.
I now wonder whether the extra weight of them (or incorrect materials) is causing too much expansion?

My engine fitted with the JP pistons had done a fair mileage when it went bang (failed water pump teeth causing jackshaft seizure and broken timing chain). Although the previous owner had receipts going back years they didn't go back as far as the engine rebuild, though judging by the engine wear and previous MOT certificates it had done at least 30,000 miles since the rebuild so had plenty of time to run itself in until I started abusing it, hence the lack of problems.

Many years ago there was a problem with county pistons for the Triumph straight six causing seizures. One of the Triumph specialists recommended an extra 1 thou bore diameter to prevent it. I had unfortunately just finished assembling the engine for my PI saloon when I heard this, so ended up running it in for 3000 miles rather than the usual 500 miles before I took it on the motorway. That was a PITA, but was only 3 months driving as it was my daily driver at the time, and I didn't do much motorway work in those days.
Neil
PS, Bullstarz Wisco pistons are for his Lexus engined Stag, and beautiful though they are they wouldn't fit!

[Stagdad]

Wow.. they are nice...What did they weigh and how much?

never heard of Wisco. Didn't want County as reports were mixed and I thought JP were the only real alternative. Wishing I had searched harder now ��

I don't imagine these will fit a TV8

[mjheathcote]

Pleased that when I rebuilt mine you could still buy new AE Hepolite pistons, domed high compression too!
Could also buy new conrods as well, that I did.
Spend hours and hours polishing the new rods to remove all the casting marks (no internet at that time but had a good blueprinting engine building book!), then along with the new pistons, crank etc had the lot balanced before I rebuilt the engine.

[mjheathcote]

Going back in time, 26 years in fact, was interested in the 'big bore' Stag engine being advertised in the Stag Magazine.
Even my notes at the time when I rang them up for prices!
Never found out, what pistons and bore did he use, how did he do the twin timing chains?
If my memory is correct, the scribble address was someone who had already had the 'big bore' engine so I could send him a letter to ask him how he felt about it!
Would all be very interesting 26 years later to find out.

[jusm]

I have heard some bad things about JP pistons seizing.
Although this post originated in 2011, I found some scoring on no 8 piston when I stripped the engine down.
I assumed it was due to a previous overheating problem and to be fair it hasn't given any more trouble in the last 5 years.

However someone sent me a PM recently enquiring whether I had honed the bores for extra clearance as they had suffered a seizure on the motorway with the JP pistons which basically knackered them.
I now wonder whether the extra weight of them (or incorrect materials) is causing too much expansion?

My engine fitted with the JP pistons had done a fair mileage when it went bang (failed water pump teeth causing jackshaft seizure and broken timing chain). Although the previous owner had receipts going back years they didn't go back as far as the engine rebuild, though judging by the engine wear and previous MOT certificates it had done at least 30,000 miles since the rebuild so had plenty of time to run itself in until I started abusing it, hence the lack of problems.

Many years ago there was a problem with county pistons for the Triumph straight six causing seizures. One of the Triumph specialists recommended an extra 1 thou bore diameter to prevent it. I had unfortunately just finished assembling the engine for my PI saloon when I heard this, so ended up running it in for 3000 miles rather than the usual 500 miles before I took it on the motorway. That was a PITA, but was only 3 months driving as it was my daily driver at the time, and I didn't do much motorway work in those days.
Neil
PS, Bullstarz Wisco pistons are for his Lexus engined Stag, and beautiful though they are they wouldn't fit!

Hi, my research so far has highlighted some concern about expansion of the Pistons and potential siezing, I guess due to the fact they are forged and also pretty meaty. They are plus .02 so I am getting a bore anyway way. I might go a fraction oversize.

Although now I am thinking it might be a better idea to resleeve back to standard and use one of the 24 standard Pistons I have somehow accumulated!