Jump to content

Advice please - gasket fire ring failure on new engine


sparky_spit
 Share

Recommended Posts

A fully rebuilt 1500 + 40thou, first started up a few days ago now and run for 20 - 25 mins at 2200 - 3200ish with varying revs, and everything was fine. I drained the coolant and retorqued the head.  I then took it out for its first drive and everything was okay, although there was some oil smoke which I assumed would reduce as the miles increased. Fast forward to today and the smoke was much worse, with some white smoke too, and rough lumpy running with only 13 miles on the clock .  No 1 plug was very oily and wet. Inside the rocker cover was a water oil mix.  I took the head off and found No1's  head gasket fire ring burned right through near to where the blind hole is - see picture. Note also the blued area of the fire rings between cylinders 1 and 2.  The compression ratio is relatively high for a 1500 at 9.6:1.

I'm hoping this is just a simple gasket failure (Payen bought some years ago) and not something I have done, or not done.  The head is flat, and so is the block with just a touch of discolouration between the middle two cylinders where the fire ring gaps merge.  When I built the engine I was very careful to make sure the fire ring recesses were flat, sharp cornered, and  properly clean, and no sealant was used. The head was torqued down to 45lbft/61NM with a slight "undo" before re-torqueing.

What is the purpose of the two blind holes close to the fire ring recesses?  Apart from providing a designed in weak spot, that is...  Is there any benefit from filling them flush with chemical metal or similar? Or is that a stupid idea?

A new gasket is on its way, but I want to give it every chance of surviving more than 13 miles.  Any suggestions are welcome as to the best way to proceed.

 

Fire ring.JPG

Link to comment
Share on other sites

Oh dear.:pinch:

My first question is to ask whether you are absolutely certain it is a fire-ring type gasket? Should have a tab at one end if so. The timing and mode of failure are very typical of a non-fire-ring gasket on a fire-ring block.

next question would be about cylinder head nut torques, what nuts were used and whether the washers used are hardened. We had terrible trouble getting our Spitty head torqued down as nuts kept loosing threads. Later replaced with flanged ones from Mini spares which solved the problem.

Finally, ref the designed in failure point, I have no idea what they were thinking of..... have read of people filling it with JB Weld or similar but not tried it myself.

Link to comment
Share on other sites

Yes, it was a Payen 1500 one with the tab at the back, and the first thing I did today was to check is said "TOP" on top.  It was about 5 or 6 years old, as it was a spare, so it's possible it had aged somehow, but I did check it over before fitting it and it looked fine.

Yes, I've used the Mini-Spares flanged nuts for quite a while now - they are very much better and just look and feel right; no problems getting correct torque.  Speaking of which, is it really necessary to re-torque once the engine has come fully up temperature?  I only ever used to do it at about 200/300 miles, basically when I'd change the oil for proper stuff, and didn't have any problems before.

I'm quite tempted to fill those two voids. Unless it creates another problem - maybe a different co-efficient of expansion (if that's the correct term?) to the cast iron making it bulge out under heat?  Having said that, there must have been hundreds of thousands of 1500 engines running around quite happily (or not...) in the '70s and '80s with that block and with no HG issues.

Do you think the 9.6:1 CR could be an issue?  It has run with that head and that CR for about 6 years (3 in my ownership) and I did have to change the HG once before as it was leaking water, but not into the cylinders.

 

Edited by sparky_spit
Link to comment
Share on other sites

Wouldn't have though 9.6:1 was a particular problem.  I do tend to re-torque after a couple of heat cycles and then again after 500 miles, but have also run up to 1000 miles before re-torquing without issues.  PI was 9.75:1 and a 308778 cam.  Vitesse is more like 10.5:1 but offset by a crazier cam.  No HG problems with eiether but then the Mk2 6 pots have proper manly studs - none of your weedy 3/8" stuff there.  I forget what my 1300 Herald was compression wise but think it was over 10:1 (with suitable nutter cam) and never had any HG issues with that either.  I side blow a HG on the Herald once 1200 form but that was because I forgot to remove my radiator blanking sheet ebfore going on a long run and cooked it......

I admit that I'm puzzled as to why you've had a problem.  Hope the next one does better!

Nick

Link to comment
Share on other sites

Thanks for the info Nick; hopefully the new one will do the job.

I've just been reading on the triumphexperience forum about those holes; they are spigot holes for the machining jig.  GT was explaining on there how he fills them with a brass plug and machines it flat to the block surface.  Someone else used JB Weld as you mentioned.  In Midget racing it is apparently common to put a valve guide in there, which is a perfect fit, and then cut/machine it off. Even though it still has a hole in it, it is enough to support the gasket outboard of the fire ring.

Link to comment
Share on other sites

I've now turned up two tight-fitting brass plugs and fitted these flush into the block.  I'll then re-fit the head with a new gasket and try again.

A thought I've had...  I've fitted plenty of head gaskets over the years and this is the first time I've had a failure like this.  It's also the first time, on well intentioned advice, that I've re-torqued the head straight after the first 20min run with a hot engine (although I did drain the coolant) rather than waiting for it to cool first.  

What do others do?  Retorque a hot engine or wait for it to cool?

Link to comment
Share on other sites

Thanks Nick.  I'll go back to doing it cold.

RR - a couple of pictures below. The sides of the void are a bit rough and the bottom is not flat, so I made the plugs a millimetre or so short and a good push fit, and locked them in place with JBweld. The hole in the centre of the plugs is to allow the JBweld to escape as they are pushed in.

I've yet to clean up the block surface, and will also need to relieve part of the plugs where they intrude very slightly into the recessed circle area. The front one, where the failure happened, is worse than the rear, which possibly shows poor alignment during manufacture?  Whatever,  I'll need a steady hand with the Dremel.

brass plug.JPG

plug fitted.JPG

Link to comment
Share on other sites

  • 2 weeks later...

I don't know whether it's a good idea to post this really, so I'm typing quietly in case my car hears me.....

The new head gasket has held up so far for about a week so I'm getting more confident that it might be okay.  What I can say, even after only using the car in running in mode, is that the balanced 1500 with Mk3 cam and a Toledo head is very nice to drive and has plenty of torque.  So far there are no downsides, although I'll know more once it has some more miles on it and has been used with some more revs.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...