leak in new head gasket

My Bedford has a gas(compression) leak from no.4 cylinder. I had all new gaskets when I had the new pistons etc. fitted.. I noticed a fine wet line just below the exhaust manifold on the top of the block in a couple of places. I had the tension on the head bolts re checked, and found them to have loosened up . Retensioned the bolts and cured the problem fo awhile.
Because the Bedford stands periods without use I spray a bit os DW-40 about the engine. I started the engine sunday and I could see the mist from the DW-40 as the compression leaked.
I have new gaskets and would like to know if anyone has used Hylomar spray on gasket sealer?
Years ago we always painted new gaskets with Silver Frost (not available now)
Hylomar is a non drying compound for gaskets, but if it doen't dry wouldn't the 17 to 1 compression force its way through eventurally.
The last gasket was fitted with a spray coat of this product.
If not Hylomar, would anyone please inform me what to use.
Changing a head gasket on a diesel bedford is something i don't need anymore than once each 10 years
Cheers Colin

G'day Colin,
Did you have the head and block machined or checked for straightness when you fitted the new pistons?

Speco/VHT also sell a product that you spray onto gaskets, it's called Copper something... You can get it from Autobarn/Repco/Supercheap etc....

www.vhtpaint.com/coppergasketcement.html

-Stu

Thanks Stu- Yes I had the block and head done.
I think it has happened because the head wasn't tensioned down enough and it started to leak.
Once a leak starts it is very hard to stop them without fitting a new gasket.
VHT. copper gasket cement sounds more like the old silver frost treatment. Thanks
Cheers
Colin

on ea falcons ford used to use permatex or avation no.3
on either side of the head gasket to keep them sealed up

ive always used aviation no 3 myself on "suspect" cyl heads/blocks ..but if its a compression leak it would be hard to seal i think

With the compression head leak check your head for being straight any pitting or damage where the gasket actually seals also check your deck height piston to block space at top dead centre, machine if heights to great use engine oil on head bolts or studs and I used to use permatex as well on the gasket or there are locktight sealers for heads as well.Also tighten head from middle to outer using the correct method

I've used Holymar years ago, it was touted as the stuff Rolls Royce use. It's didn't used to be expensive, I'd give it a go. Why did you head bolts come loose, with the gaskets that you get today, generally once the head is tensioned it is right, years ago you had to retention them and set the valves again after the first 1000 miles or something. Best be put a straight edge on it all while it's apart maybe.

If you had the block machined when you fitted the pistons how much did they take off? is the compression still 17 to 1 or higher, just a thought had the same sort of problem on a landcruiser once, fitted it with a thicker gasket to lower the compresion a bit and havent had a problem since

does this engine have liners? if so what is the liner protrusion? incorrect liner protrusion will blow head gaskets. use guide studs as suggested as this will let you lower the head on perfectly. its not hard to slip and damage a gasket while trying to lower a head. clean both surfaces shiny with emery tape and clean all oily residue off with petrol or brakeclean on a clean rag. Holymar is good gear. it leaves a soft coating like what most head gaskets have on them now. you shouldnt need to re tension heads in this day and age. if you do just do one bolt at a time.

Try painting the gasket with silver paint , i remember seeing this trick when i was younger .