Head Gasket Failure. Possible Causes.

[Al Weyman]

Caused by too much load on the bearings, did you check that link page I posted.

[Tim Falce]

Yup, thanks for that, I've also been depressing myself reading the various causes of detonation. I just hope it hasn't fractured the crank.

[GORDON STREETER]

Originally Posted by Al Weyman

I would cc the head, and do the same with the block with piston at TDC what else can you do?

Well for one thing you would have a hell of a job with domed pistons as they normally stick out the top .

[Al Weyman]

Its perfectly feasable to do but yes you would have to make up a little jig, where there is a will there is a way ;-). A far easier way of couse is if the spec of the piston is known. Here is a nice little online easy to use C/R calculator I use which allows a negative value for for the piston dome to be factored in. http://cochise.uia.net/pkelley2/crc.htm For a rough calc allow about -10cc for the dome and see what it comes up with.

I would doubt its fractured the crank, I got away with a good polish (should I rephrase that?) and mine was seriously bad!

Here is a way of measuring the dome using a flat piece of simple plastic. This is for a Supra so measurements may vary but the theory is there.

To measure the piston dish/dome volume: (I still had the short block assembled)

Move the piston about 2 inches into the bore
apply a ring of grease around the bore just above the piston
move the piston up so the rings catch the grease and create a seal
I left my piston about 0.24" below the top of the block, that number doesn't really matter as long as you know it.
then apply grease on the top of the block around the bore
place the piece of plexi glass on top of it and make sure the grease seals to the plexi glass
Use the graduated cylinder and find out how much volume you have

Then use the 0.24" and the bore to calculate the volume of a cylinder (basically what it would be if you had a flat top piston)
Then take your calculated volume minus your measured volume and you should have a good idea of the dish/dome volume.

[zefarelly]

sorry I'm late

I've been financing Messrs Payen (I've tried all the posh variants, no difference other than cost, some expensive ones are worse) well over the last year as I've been trying to gain something, and have done, albeit briefly, so now I'm reverting to 2006 spec, competitive (then) and utterly reliable

my conclusions are Anything over 12:1 is failure, 11.5-11.8 seems fine, 11:1 or less will run on pi55, 12.2 blew with sunoco 105 at Lydenn (11:1 with 2 gaskets) and 12.5 blew at SPa last year, holing a piston at the top of the Kemmel straight. my engine doesn't like really high CR. I am running flat everything . . . . wire ringing works as someone else will testify and that is the way to go for really hot motors but it won't cure advance related det or sh!t fuel. I've used 'posh' petrol and the difference there seems negligible over super/CVL, at least in my limited experience.

power wise I've gained very little extra at high CR and wasted lots of time and money so I'm going 11.5:1 32 max advance . . . aa a minor aside, I'm restricted to 40's and have found the limit

If |I don't cure my problems maybe I'll buy an Anglia and take that to Spa

[Al Weyman]

And get some Jap bike carbs on it and you will be away :-)

[zefarelly]

I think I already proved otherwise on the 40's, points too

[Al Weyman]

You certainly did!

[GORDON STREETER]

Joe, throw those lawn mower carbs in the bin and use mine. That's where you're going wrong !

[zefarelly]

rules is rules Gordon

I have a pair of Italian weber 48's under the bench

[Tim Falce]

Originally Posted by zefarelly

rules is rules Gordon

I have a pair of Italian weber 48's under the bench

Italian Webers are totally useless, they give trouble and I've heard they cause fires. Tell you what I'll do you a favour take them off your hands if you like.

[Al Weyman]

All very interesting chaps but what caused the head gasket failure!!!

[Tim Falce]

I thought most were going along the lines of detonation. I don't think the gasket was seated properly and one side of the sealing rings may have been slightly offset and judging by the burns on 1 and 2 it could have caused a hot spot. Not sure about No.6 though.
I will try sitting another gasket on there to see how it fits.
Question, and it may be silly; When an engine is rebored, how is the boring machine lined up with the block, would it be possible for it to run out of line from one end to the other?

[terence]

That would depend on the actual Boring machine/operator Tim.Run a straight edge on the outside of the bores,that should give you a rough idea.
BTW Tim,Webbers were always made in Italy,the crap one's come from Spain,you can easily tell the difference,if they are Spanish,they'll have a lot of "Flashing" on the bodies.

[Al Weyman]

The boring machine bolts to the block as far as I am aware unless there is modern ways of doing this.

I noticed the other day that Edelbrock 4 barrel carbs for yanks are made by Webber at least they have the name engraved on the body.

[Tim Falce]

Originally Posted by terence bower

BTW Tim,Webbers were always made in Italy,the crap one's come from Spain,you can easily tell the difference,if they are Spanish,they'll have a lot of "Flashing" on the bodies.

Yes, I know, I have a set of Spanish Webers, pre when they went broke afaik, and the castings are fine compared with my mate's new ones, which I feel I must add are a jolly fine looking set of carbs apart from a bit of roughness on the castings.


BTW, I am pretty sure I have a CR of 9.6:1

[Tim Falce]

Originally Posted by falcemob

BTW, I am pretty sure I have a CR of 9.6:1

Or it may be 12:1

[Al Weyman]

It may even be a diesel! :-)

[GORDON STREETER]

Originally Posted by falcemob

Question, and it may be silly; When an engine is rebored, how is the boring machine lined up with the block, would it be possible for it to run out of line from one end to the other?

Normally the boring machine is centralized up with the bore that it's cutting at the time. So unless the block was machined wrong from new this shouldn't be a problem.

[GORDON STREETER]

Originally Posted by zefarelly

rules is rules Gordon

I have a pair of Italian weber 48's under the bench

Still lawn mower compared to mine !

[Al Weyman]

Sorry to quote small block GM V8's but the theory is the same. I have read that a phenomena known as 'core shift' can happen on these blocks during the casting process that can cause bores to be ever so slightly out. Thats probably why the small block has a generous 35 thou or so between the bore and the gasket. Yours is probably a bit marginal in any case but at 60 thou over bore and high compression may be all getting on the ragged edge side of reliable.

Yes but we all know you have a genuine FIA 1200cc Anglebox with the correct homologated single choke down draught carb Gordon that can race anywhere! :-)

[GORDON STREETER]

Originally Posted by Al Weyman

Yes but we all know you have a genuine FIA 1200cc Anglebox with the correct homologated single choke down draught carb Gordon that can race anywhere! :-)

At least you believe me Al

[zefarelly]

Originally Posted by GORDON STREETER

Still lawn mower compared to mine !

I've got a ransomes . . . low on power, but its got enough torque to put your back out (or in maybe!)

[zefarelly]

ok . .. 12.2 CR failed at Lydden . . .I've sliced 1.5cc from the chambers today so hopefully 11.7 will prove a bit more reliable . . .

now . . .which head gasket? . . . . .

[Al Weyman]

A thick un!