Blown Head Gasket

[Darren Groves]

So after only 11 months & 4000 miles my head gasket has blown between No.1 & No.2 cylinder. The gasket was a Payen, so quality should be fine.

The engine is modified, but nothing nothing too drastic. Bored out to +60, fast road cam, larger valves and CR around 9.6:1.

Any reason why is should fail where it did, or just bad luck?

[Pete Lewis]

Hi Darren as you ask read and do whats needed I would hate to suggest it was undertorqued

but thats a big blow right in the weakest link and smallest supported zone

 

thers no signs of blow by on the fire rings all clean and looking good , apart from the blown out section thers some signs either side of the breach.

 

May be bad luck or just west country classic gremlins

 

pete

[Darren Groves]

Hi Pete,

 

I guess under-torqued is a possibility, though I did re-torque twice after the initial fit with a decent quality Snap-on wrench.

 

I guess the fact it's bored out to +60 only makes a weak spot weaker again.

 

Will refit once the new HG has arrived, hopefully just gremlins. If it happens again I will reassess.

 

Darren

[John Bonnett]

Hi Pete,

 

I guess under-torqued is a possibility, though I did re-torque twice after the initial fit with a decent quality Snap-on wrench.

 

I guess the fact it's bored out to +60 only makes a weak spot weaker again.

 

Will refit once the new HG has arrived, hopefully just gremlins. If it happens again I will reassess.

 

Darren

Oh dear Darren. Mine has been been bored out to plus 70 and a c/r of 11.4:1

[Guest]

Hello Darren.

 

I thought my torque wrench was spot-on until I took it to the local garage. The garage had their Snap-On franchise chap check it on his calibration unit. It was 27% below par - so for 100lbs it was only delivering 83lbs; which is quite a difference.

 

It has not been mistreated and always left at zero when not in use; over time the accuracy decreases even with infrequent use.

 

In fairness it was not an electronic wrench, which is the preferred item these days for accuracy.

 

I needed to torque the head on the Vitesse, so they were kind enough to lend their wrench over the weekend.

 

May well be worth having your local garage check it for you, if they are willing.

 

Just a thought.

 

Regards.

 

Richard.   

[Pete Lewis]

make a lever 12" long with a 1/2" square hole in the end  and press the lever against the bathroom scales 

 

60lbs at  1 Ft = 60 ft lbs   most wrenches can be adjusted , 

 

Pete

[dougbgt6]

I clamped the business end of my wrench side ways in my bench vice. Then set the wrench and hung a bag of dishwasher salt near the vice. Then moved the salt towards the other end until the wrench clicked. Measure from vice to salt and feet times salt = ft lbs 

[Pete Lewis]

Doug, Too much salt is supposed to be bad for you , it rots the cars

 

But a nice simple way to calibrate so how many salt lbs to a decanewtonmetre

 

Answers on a post card

 

pete

[Darren Groves]

 

 

In fairness it was not an electronic wrench, which is the preferred item these days for accuracy.

 

 

 

Thanks for the replies guys.

 

The torque-wrench I use is electronic, it buzzes & vibrates, no clicking! Are we saying that electronic ones are more accurate and less in need of calibrating?

[Pete Lewis]

Yes they use a strain gauge rather than mechanical springs and plungers and levers

 

I have some but tend to use my trusty norbar ive had since I was 21 used to calibrate them at the factory , we had hundreds throughout the assembly lines I was instrumental in devising a full truck torque audit back in 1967 when design only specified safety critical fixings all the other fixings then had to rethink the tooling and air supplies volume not just pressure , hose lengths all play a big part

we devised with atlas copco a rack of sockets so one air gun could do different sizes

as you removed the socket it changed the air supply and controlled the torque once the torque was

attained it applied a dab of blue paint , so easy to inspect, no blue no torque

 

Inervated stuff in the 60s and 70s

Pete

[Guest]

That is correct Darren.

 

I still think, electronic or not, it's worth getting it calibrated before torqueing down the head again. At least you can rule out 1x possible.

 

Regards.

 

Richard.

[dougbgt6]

Not so sure about electronic, I have scales, I'm pounds heavier or lighter depending on air pressure or temperature. That's what I tell the Doc anyway.

[Ben Caswell]

make a lever 12" long with a 1/2" square hole in the end  and press the lever against the bathroom scales 

 

60lbs at  1 Ft = 60 ft lbs   most wrenches can be adjusted , 

 

Pete

 

I wouldn't trust the bathroom scales mine over read by loads :-)

[Pete Lewis]

But calibrating means you dont need to lean forward to see the reading

More salad Grrr

 

 

 

pete

[JohnD]

OR

 

 

I'm sure I wrote about this before.  This particular wrench was under reading and I cracked a block as a result.

It's important to check your wrench annually, and before an engine build or a major sevice that needs the head off.

 

John 

[Darren Groves]

Just tested the electronic Torque Wrench I always use, I hung a 22.560lb weight at 14" (1.166ft) from the centre of the drive. 22.56 x 1.166 = 26.3185 lb-ft, the wrench read 26.4lb-ft so well within tolerance. Worth doing, at least I can be sure it will be set correctly.

 

Just out of interest I dug out my old 'clicky' one I used to use, that was under reading by just over 20%.

[Steve P]

New Payen isn`t the same as old Payen,try and find a Nos one.I had the same issue on a six.

S

[Waynebaby]

Just to allay folk's fears that their torque wrenches are invariably miles out of calibration you might like to hear what mine were like. Having been spooked by Darren's head failure and being on the point of re-torquing the new head on the GT6 I took my two trusty wrenches to the local calibration facility (there aren't too many advantages to living in Teesside but having a variety of engineering services on your doorstep is one of them) A couple of hours later and I found that the largest margin of error across the two ranges was <1.5%. Neither of the wrenches had ever been calibrated before and one of them is at least 15 years old. Having said that they don't get dropped or used as hammers either. The price of re-assurance? £96 including VAT.  

[Darren Groves]

So the engine is all back together and running fine. With the cause of the premature failure still a bit of a mystery, Pete's suggestion of under-torqued was a good one, but as the wrench I use tested OK this seems unlikely.

 

Assuming that the Payen Head Gasket was of sufficient quality, I can't help pondering why it failed early. Now the head was skimmed a fair amount to raise the CR to be better suited to the Fast Road Cam, so it's flatness is pretty assured, BUT what I didn't do was have the block skimmed. So what are peoples opinions that it could be due to the top of the block not being 100% flat and should this be done as a matter of course?

[Pete Lewis]

I think wait and see what happens , blocks are pretty stable where as the head pants about on its fixings

 

And less stable so is more prone to loose its flatness.

 

torque it to the max and retorque after a few runs

 

reset the tappets afterwards

 

pete

[Darren Groves]

Hi Pete,

 

Thanks for the reply.

 

I re-torqued this morning after about 60 miles of so, was planning to do again after a few hundred. Valve clearances had closed a little afterwards, so all reset. Done another 30 miles or so since and thought I'd have a look over the engine for leaks etc. as you do. I did notice a glistening of what I assume must be oil between the mating faces of block & head. Now this has been a trait of this engine and head combination, has been a bit of a losing battle for it to be relatively oil tight, unlike my previous lump which was pretty good until it went bang!

 

I like to worry 

[Pete Lewis]

The joys of classic ownership

 

They sit quietly in the garage just waiting to get one over you

 

I wonder if calming whale music played all night will help the cad or you !!

 

its a plague that the more you try the worse it gets, like whenever you find the problem the solution

never cures it

 

Good luck with a good few more miles this time

 

Pete