blowing head gasket

[Austin in the Shed]

My own theory for the cracking is when the stud is tightened down the run out on the thread acts as a wedge and splits the weak area. Also then when tightened further opens up the split.
It would be better if the thread ran out into an undercut to prevent this happening.

[Parazine]

A reminder that it's possible, with a block that has been lined, for the original cylinder bores to be so thin and corroded that structural integrity is lost. Effectively, the top deck of the block is no longer connected to anything except around the edges and it starts to distort. 

The symptom is persistent head gasket failure.

My advice would be to find a re-boreable block and rebuild the engine.

[Captain Mike]

Thanks all
I guess I will be locking into a "new" block and possibility a new head, but at this point I have nothing to loose by trying to seal things up, the water leakage is coming from the stud with the Heli coil so I will be looking at that first, Can you buy head gaskets in bulk ? the next one will be the third, however I did not look closely at things the first time I replaced the gasket as there were some of the head studs loose which I thought was the problem

Poor old girl is getting incontinent in her old age, I will re post if I cure it with the third try
Thanks for all the help and suggestions

[Howard Wright]

Hi Mike

With regard to water/oil coming up through the stud holes, I solved this by putting sealer (see below for type) under the washer below the head nut. It’s also a good idea to put a bit around the helicoiled base of the studs.

I use a light smear of Loctite SI 5990 copper silicone on both sides of the head gasket, it’s been recommended here before.

Good luck

Cheers

Howard

[Chris KC]

Mike, sorry if teaching to suck eggs, but basics first -
1. Have you checked both the head and block faces are FLAT? Especially look out for a hollow in the middle of the head.
2. Are you following the correct tightening sequence? n.b. I normally tighten in increments and go round the sequence at least 2 or 3 times.
3. Are you applying a suitable torque (~20lbft), with a torque wrench, engine COLD? (n.b. you don't mention what head you are using? Especially if an alloy type I suggest re-tightening after first run, but again, with the engine COLD).
4. Are you dressing the gasket with anything? I only ever use grease but others recommend various sealants. 

You may well know all this, if so I'll shut up. But it troubles me that you have made a diagnosis without (visibly) eliminating other possibilities.

My block is cracked and weeps up the centre stud, but it does not blow head gaskets, so far at least.

I would not contemplate "filling" craters in the block surface with glues/fillers. A better course is either to lap it on a surface plate or to have it skimmed, until clean and flat; though be careful not to remove too much metal as it can cause other issues.

I sometimes wonder being #1 in the tightening sequence may be a factor in blocks cracking at this position - though I'd struggle to explain that with logic.

[Tony Betts]

that furface looks like its not had any attention for several decades.

if the centre row of studs are cracking, then for me the block is dead.

as dave dye suggest the run out on the stud thread dosnt help, but thats only half of what causes the crack.

its like bending a 1mm sheet of steel, easy on its own. but put a FLAT 2 inch steel plate on top. NOT so easy.

if the head and block are warped, the stud will pull the block surface upwards into the void. and crack the surface.

put a flat head against a flat bock. and the tensions can be 10 fold without problem.

tony.

[steve davidson]

Hi Tony,

Maybe a silly question but how flat is flat?  I blew a head gasket and upon stripping it down I found the head was perfect but I could detect some slight warping on the block.  Nothing big enough to get even my thinest feeler gauge (.004") in but with a light behind the defect was visible.  I'm thinking that a defect that small will be manged via the gasket but interested in your thoughts.

[Chris KC]

I won't try to put words in Tony's mouth Steve, but it's possible for a block or a head to have a cavernous hollow inside but no measurable gap at the edges. Testing around the edges with feelers alone may not be enough. 
Anyway my thinnest feeler gauge is 1.5 thou, if I could measure 0.004 I think I'd keep on lapping.

[Tony Betts]

thanks chris, your reply is preity much the same as mine would be.

as the mane warp on a head, is in the centre. how did you measure 0.004

the obvious answer is if you can see 0.004 at the edge of the head or block, then surely if its bowed. this will be much more in the centre.

this is were i never use things like flat glass to do a home job, because you never really know what you end up with.
i would only use a machine company i trust to resurface things. as others rush a job. overheat the surface and it bowes again when cool.
and i prefur a surface finish to be done on a profesional surface grinder, rather than a miller. with a surface grinder, you can do a final grind after the head or block has cooled. FLATTER THE BETTER.

i have my own jones and shipman 540 surface grinder, sadly not needed to use it for many years. as all my heads and blocks now seal correctly. so need to recomision it some time. and i might start up resurfacing for people again after seeing what many are now charging.

tony

[Colin Reed]

HI TONY,
Your advice is spot on,
When using modern Gasket Material the surface needs to be smother as they do not fill in irregularitys as well.
Also you are asking to much of The material to fill in hollows , Torquing to a higher flb does not help more likely pulls the thread up.
The type of Grinder you have Tony is great as it allows you to grind a range of items connected to Engines.
Also as you pointed out the Operator needs to take there time.
I have a Wright 12 inch table grinder made in Halifax for automotive work , the stone works in the horizontal so grinds the full width of the Block or head as it is moved horizontaly
has done a lot of work.
Colin
NZ