JP Head Gaskets

[frangar]

Hi

 

My JP seems to get through a set of head gaskets about every 2 years (roughly around 500 hours)...the last time they went a new liner was fitted as the original one was deemed to be a little low...however its now blowing from both heads although the front one (which hasn't had a replacement liner) seems worse.....I will be taking the heads off over the weekend..and have replacement gaskets etc but I'm beginning to wonder why I get through head gaskets? The last time they were replaced by a well known vintage engine rebuilder but before that I have done it myself but the time they have lasted seemed to be the same!!

 

The gaskets have been of the copper/asbestos(or similar) type....I have used Wellseal when I replaced them although I think the "pro" didn't use any "gunk" and I have torqued the studs down to about 150lb/ft

 

Although I wont know what the heads are like till I get them off this time they didn't show any signs of cracks etc...

 

They are blowing round where the push rods come up and also slightly on the front of the front cylinder. There is also a lot of "air" (compression gas) in the coolant.

 

Anybody got any thoughts as to anything I could be missing or could do to make them last longer? The engine was worked fairly hard on the last trip...we were on the Avon & Severn and now have the correct size prop (thank you Crowthers) fitted so the engine is probably working harder than before but hasn't shown any signs of overheating.

 

Cheers

 

Gareth

[Timleech]

Hi

 

My JP seems to get through a set of head gaskets about every 2 years (roughly around 500 hours)...the last time they went a new liner was fitted as the original one was deemed to be a little low...however its now blowing from both heads although the front one (which hasn't had a replacement liner) seems worse.....I will be taking the heads off over the weekend..and have replacement gaskets etc but I'm beginning to wonder why I get through head gaskets? The last time they were replaced by a well known vintage engine rebuilder but before that I have done it myself but the time they have lasted seemed to be the same!!

 

The gaskets have been of the copper/asbestos(or similar) type....I have used Wellseal when I replaced them although I think the "pro" didn't use any "gunk" and I have torqued the studs down to about 150lb/ft

 

Although I wont know what the heads are like till I get them off this time they didn't show any signs of cracks etc...

 

They are blowing round where the push rods come up and also slightly on the front of the front cylinder. There is also a lot of "air" (compression gas) in the coolant.

 

Anybody got any thoughts as to anything I could be missing or could do to make them last longer? The engine was worked fairly hard on the last trip...we were on the Avon & Severn and now have the correct size prop (thank you Crowthers) fitted so the engine is probably working harder than before but hasn't shown any signs of overheating.

 

Cheers

 

Gareth

 

Have you measured the liner projection above the block? If it's below spec then either the top of the block needs skimming (complete strip down beforehand!) or specially made shims under the liner flanges. The top of the block might be distorted, but that's difficult to check without pulling the liners first.

Have the heads been skimmed? one of the first things to do if you have head gasket troubles.

I would use Wellseal, did you follow the directions about allowing it to dry before assembly? Also if using Wellseal you should retighten after 10 mins or so, to allow the compound to squeeze out.

Loctite used to do a clear hardening compound which was good for troublesome head gaskets, it did need the whole assembly & tightening to be done quickly before it started to harden, can't remember the number & haven't been able to find any reference to it recently.

 

HTH

 

Tim

[frangar]

Cheers Tim, thanks for the speedy reply!!

 

 

Have you measured the liner projection above the block? If it's below spec then either the top of the block needs skimming (complete strip down beforehand!) or specially made shims under the liner flanges. The top of the block might be distorted, but that's difficult to check without pulling the liners first.

 

The last time it was done (by the pro who I dont think belongs to this forum btw!) it was both liners were supposed to have been checked but I will check it when I get the heads off this time.

 

Have the heads been skimmed? one of the first things to do if you have head gasket troubles.

I would use Wellseal, did you follow the directions about allowing it to dry before assembly? Also if using Wellseal you should retighten after 10 mins or so, to allow the compound to squeeze out.

 

One of the heads...the one thats now blowing badly...was replaced as the orginal one was thought to be cracked so it was thought prudent to replace. Yes I did let it set....do you agree that 150 lb/ft is roughly the correct torque setting?? I thought I did recheck it after it had been on a while....being a marine unit tho once its back together its impossible to check the nuts that go round the push rod tubes cos the valve gear is in the way...I can get the rocker shaft out of the front head but the back one cant be moved because of the slicencer...

 

 

Once again thanks for your advice...Will see what I find over the weekend!

 

Cheers

 

Gareth

[Timleech]

One of the heads...the one thats now blowing badly...was replaced as the orginal one was thought to be cracked so it was thought prudent to replace. Yes I did let it set....do you agree that 150 lb/ft is roughly the correct torque setting?? I thought I did recheck it after it had been on a while....being a marine unit tho once its back together its impossible to check the nuts that go round the push rod tubes cos the valve gear is in the way...I can get the rocker shaft out of the front head but the back one cant be moved because of the slicencer...

 

 

Once again thanks for your advice...Will see what I find over the weekend!

 

Cheers

 

Gareth

 

What I meant was - pull the heads down. Wait 10 -20 minutes, then go round all the nuts again. Yes it would be nice to do it agai n after a run, but a lot of work.

120 to 150 lbft sounds about right to me, I don't think you would want to go any higher.

 

Tim

[steamraiser2]

Although Tim is quite right that the head and block may require skimming if they are not flat I would not be at all surprised if the problem lies with the gaskets themselves. There are a lot of South Asian gaskets around which are inferior to the original Lister ones. There are several British gasket firms around and my advice would be to get decent gaskets rather than risk the cheap imports. You don't need gasket goop at all. Are you running your engine with the changeover valves on high compression?. Running hard on a river on high compression with low quality gaskets is tempting fate in my opinion. The JP range are robustly built and head leakage is not a congenital problem. If you are experiencing problems check that the heads and block are flat, the gasket faces are clean, waterways not scaled or sludged up and that you have quality gaskets. Ensure that you tighten the head to the correct torque in the proper sequence, leave it for a while and retighten it and you should be fine. Some of the JPs I do have not been apart in seventy years which tends to support the solidity of the orignal design!

[frangar]

Thanks Tim, Will leave as you suggested and have a retighten although I always say a little prayer in case I snap a stud! I am going to replace the studs this time just to be on the safe side.

 

Steamraiser2....thats a vey good point about the quality of the gaskets...I think the last couple of times it has been done with gaskets that might have well come from the Asia source....I have now tracked down some new old stock Lister ones (Made by Coopers)....I understand that Coopers got rid of the tooling for the JP's so I presume unless you can get old stock other new ones are probably sourced from overseas. They are more expensive but if they last then its a lot cheaper than taking the heads off every couple of years!

 

I always run in low compression only using high to start. As to the sequence there is nothing in the manual about a tightening procedure...in lieu of this I just go diagonally...is that the best practice?....I will probably use Wellseal just to seal the waterways if nothing else...I think the engine was sea water cooled originally (its a Marine unit) so there is some corrosion around the waterways.

 

I'm just grateful that it waited till we were back at the marina to fail...think its going to be a busy weekend! However it does now justify the 2 Britool Whitworth socket sets that I got from car boot sales...I told the OH that they would come in useful!!....even though I had the required sizes already...ssshhhhhh!!

 

Also does anyone know of a machine shop in the Midlands that would be capable/trusted to check/skim the heads as required?

 

Cheers

 

Gareth

[Canopus36]

http://www.classicandvintageengines.co.uk/

 

 

Bradbury Engineeering are currntly doing my JP3 heads and come well recommended.