Technical Headgasket guide!

Currently reading:
Technical Headgasket guide!

Joined
Oct 1, 2017
Messages
5,008
Location
Edinburgh Scotland
It does sound like HG..

I wasnt expecting the dash of oil to change anything..

Are you capable of doing it yourself?

Its a days work.. but need all the right handtools... ;)

I agree, this certainly has many of the indicators for a failed head gasket but the fact that all four spark plugs are looking the same is bothering me (all four equally fouled with no signs or rusty or washed out difference on 2 and/or 3). I'm not feeling that we yet have a definitive diagnosis of the gasket having failed.

I mentioned in another thread recently about a cylinder leak down test and I think you might learn a bit more if you did one here. A lot of better equipped workshops should have the gear to do it. Without going into detail, it uses compressed air, introduced into each cylinder in turn, with both valves in the cylinder being tested in the closed position. The equipment then measures the %age of leak for each cylinder - which I don't actually pay too much attention to, unless it's showing something ridiculous, but what can be very valuable is that the compressed air will escape anywhere it possibly can! So, if an inlet valve is not sealing you will hear a hiss from the inlet (best to take the air filter off first and I like to use a length of small diameter flexible hose stuck in my ear so I can stick the other end into the air intake). An exhaust valve will hiss from the exhaust. (bit of tubing in the ear is an even better idea here too - saves a very dirty ear!) Excessive piston blowby hisses from the oil filler, or other crankcase orifice of your choosing and head gasket to water passage failure gives lots of easy to see bubbles in the radiator header. There's a lot more you can diagnose with it too:
https://www.aa1car.com/library/leak...wn or cylinder leakage,of all the spark plugs.

The piston blowby hiss can be difficult to asses because there will always be ring leakage but after you've listened to a few you soon get to know how loud a hiss is about right. The leak guage is a big help for this too.

I was really the only one in our workshop to use this tool much and I liked it so much that I made my own cheapo version to use at home by smashing the ceramic out of a couple of different spark plugs (one short reach "standard 14mm and one from a Ford Pinto) and brazed a male airline connector to them so I could introduce compressed air into the cylinders. No gauges of course but you can tell a lot from the where the hisses are coming from and how loud they are! Now a days I see the kits for sale on ebay for under £20 so I think I'd just buy one.
 
Joined
Oct 1, 2017
Messages
5,008
Location
Edinburgh Scotland
I had none machined..all appeared flat

Interesting Charlie. We had a nice big Moore and Wright engineers straight edge in our workshop. All heads were checked using this in multiple positions with feelers. In line, corner to corner and diagonally. As long as you couldn't get a 1.5, maybe 2, thou feeler under it you were good to go.

I've never been a fan of just automatically facing off a head "just in case" and some you can't anyway because of their design. (I seem to remember the Ford 1600 crossflows were the first like that I bumped into - a flat faced head with combustion chambers formed in the piston crowns. If you tried to surface the head you soon found you were chewing into valve seats I think?). I haven't done more than a couple of diesels but I know they can be particularly difficult if you mill/grind the face because they often have selective thickness gaskets on reassembly - take too much metal off and you really are into the "sticky stuff" depending on piston design ie, protrusion. We actually had a slightly less long straight edge so you could check block deck faces as well but I never found one that wasn't perfectly flat (or as near as) so it saw very little use.

Now, at home, I check heads using a length of ground steel flat stock which was given to me by an engineering shop near me when I was into rebuilding Imp engines. Checked on their big surface plate and I couldn't get even my thinnest feeler between it and the surface plate over the entire length of the bar.

PS. always checked the block face/cylinder tops on the imps though!
 
Last edited:
Top