Took the head off the 300 TDi Saturday no cracks and flat as a witchs etc but the thermostat housing was badly sealed 3 bolts came out and one awkard bleeder came out down to the last 1/2inch and siezed leaving a 5/16 stump no joy with the moles nor welding a nut on ( 4 times ) which only suceeded in removing the last 1/8 when the weld sheared off so its down the engineers for a drill and tap job tomoro I might ask him to give it a polish at the same time. Derek Disco 200Tdi Kato Disco300Tdi Miles
When I got my first alloy engined vehicle in the '70s I also got the factory workshop manual. And it insisted you used a special thread sealer anywhere a bolt or stud went into the ally. This stuff has four basic functions.
1) It prevents corrosion in the threads.
2) Seals the threads - useful where they go into the water jacket.
3) Locks the thread once it sets.
4) Lubricates the thread thus allowing the correct torque setting where applicable.
It's called Scotch-Clad 776 and is made by 3M. It's an industrial product really for the aircraft industry so not available retail in small quantities. The smallest size is a 1 litre tin. Which costs about 15 quid. And will last a DIYer many years - although it's rather like a paint in that it will go off eventually as it's used up and there's a lot of air in the tin. Decanting it into a smaller ones so there's no air would probably slow this down. I'm only on my second tin.
Later factory workshop manuals for the same engine don't mention it. But I wonder why since steel to aluminium threads remain a problem under some conditions.
It could be there is a similar Locktite product. But this stuff is rather different than most of those in that it's a thick clearish goo rather like cellulose varnish. And indeed cellulose thinners is used to clean it off used components before re-use.
I found the recent supplier by Googling on 3M. A place near Southampton which would do mail order but had a fairly high minimum charge of IIRC 50 quid. Luckily they had other products I could make use of to make that up.
The water pump bolts go because a couple of them corrode where water goes past them (or mine seem to have done). There are a couple of the v8 inlet manifold/head bolts that are similar.. Always use a torque wrench or a small ratchet so you can feel what you are doing and not abuse it. Other than that it is sods law that the hard to reach ones break :)
Derek - drilling and tapping/helicoiling stuff yourself isnt too tricky
- though since its off anyhow you might as well get it done while he's polishing it (its a set rate for helicoiling stuff at the place i use)
I have just had problems with three bolts on a 300tdi cambelt casing. The three bolt heads were chewed up using a socket (10mm) and had to be ground off, yes they were in an awkward place. They were only recently installed using a torque wrench and therefore should have come off easily which they did (Using fingers) when their heads were cut off suggesting that there was a considerable amount of friction between the head flange on the bolt and the casing. When replacing them I made sure that there were no burrs on either the bolthead flange and the casing. Any other reason why this happened?
Thats a good point and as it happens I have some Loctite thread sealer ( a smallish tube a bit bigger than super glue ) I usually smear a spot of greaseon threads where I suspect the possibilty of water ingress I have to say that at some point a mong has been involved with the engine maintainence evidence supporting includes the lack of any sort of a gasket on the thermostat housing, a very loose couple of head bolts, only four valve caps under the rockers I say under, one was loose in the rocker chest . Derek
It's not so much how much air is in the tin, but the air liquid interface. I use the easy-but-messy method: clean plastic bag turned inside out and pushed down into the tin till it touches the surface of the liquid. I used to do the same with photographic chemicals years ago (in that case blow it up like a paper bag to fill the space better) - the concertina bottles were too expensive.
If the quote is over 60 you might look at spark erosion. I had an exploded bolt in one of the Beemer's stainless exhausts I tried and couldn't weld anything on to the stub successfully, but spark erosion left the original thread clean and virtually undamaged. It wasn't cheap at around 60, but it couldn't really be helicoiled and the alternative was a new RH exhaust at circa 180 UKP.
Job done and in less than 24 hours 7thou skimmed bolt drilled out and helicoiled head gasket set and a 1.6mm head gasket core plugs replaced and the head pressure tested at operating temperture and the whole lot came to £100.21 so you can guess they are likely to be getting more business off me in the future.
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