Head Gasket

[bison]

Gentlepeople,
Here is the tale.
When I got Rene ,1976 TL 875cc, the head gasket was gone due to a very knackered water pump and a stuck thermostat. I duly replaced the head gasket etc, car ran great, still used a tiny bit of water but didn't stop us from driving down to Normandy from Edinburgh and touring around in 2008. Now after laying up last year I've done all the bits and bobs for his MOT to find tonight the head gasket away again. I checked the oil, a bit above the level and very cloudy, topped up the water and checked the overflow bottle, sure enough, a bubble every few seconds, and looking at the centre head bolt ( the one outside the rocker cover with the throttle cable clamp under it) water and bubbles coming from that.
Just removed the head and the gasket doesn't have an obvious track/leak.
Now, for reasons lost in the mists of time, I didn't have the head skimmed when I relaced the gasket the first time, but I will this time!.
What's bothering me is, what are the chances of it being the bottom liner seals that are leaking?. They weren't disturbed when doing the job this time or the first time. It really seems to be a warped head that's causing the problem, but I though it would be prudent to ask your collective opinions?.
Thanks,
Alan.
PS, off to Normandy for some R4 touring again in June!!!

 

[benchseat]

I had a similar problem with my 845cc machine (at about 130,000 miles). Air bubbles in the coolant bottle but no mayonnaise in the oil : but I had previously blown a couple of radiator hoses which must have been the leak pressurising the cooling system. A head skim + new gasket cured all problems and the performance is somewhat improved - particularly the idling after a fast run (very lumpy before, smooth now).

 

[bison]

Aha, now that you mention it, the idle speed is higher than I remember on my last 4TL, and a bit lumpy too. Thanks for that info.
Alan.

 

[angel]

It is very rare for a head gasket to go without the head warping first. The liners are not that easy to move (on such old engines they are held by rust/scale). Also, leaking from the liner base seald would not make bubbles in the coolant or around the fixing bolt as you describe...

 

[bison]

Hi Angel,
The head was indeed warped, I put it on a surface table and could get a .005" feeler gauge underneath, so I refaced the head anyway, I had to take 012" off to get a clean surface. The liners certainly don't rock about, they seem quite firmly in position, so I think you are right about the corrosion etc.
Thanks,
Alan.

 

[Steve Hennessey]

Do make sure that everything is spotless and free of grease, oil and any corrosion before re-assembly. In particular, ensure that the threaded holes in the block are empty of any oil or water, the threads are clean (I used a tap and then blow out with an air line) and the threads on the head bolts are also clean (I use a die or a nut). I use a smidgen of copper grease on the threads when assembling and this ensures that the correct torque figures are obtained.

 

[bison]

Yes, a couple of the head bolts are carboned up where the head must have been leaking, I'll clean them all up on my wee lathe and run a tap down the threads, can you remember what thread they are?, I'll go down to the workshop and borrow a tap incase I don't have one at home, from memory I'm guessing 10mm standard pitch?.
Thanks,
Alan.

 

[Steve Hennessey]

Sorry Alan, can't remember the thread size - pretty standard though.

 

[angel]

10x150, as you guessed that's a standard size.

 

[bison]

Thanks people,
Got the head all done, running nicely, only water in the cooling system so I can flush it all out after a few miles. I had to re adust the carb a lot, it would seem the head has been leaking for some time. I took advantage of the head being removed to install some sound insulation on the bulkhead next to the timing chest, hopefully it will make driving down to Normandy less of a chore.
I will fit my Mikuni carb next week and see how it works.
Alan.