Head Gaskets

[Mike Farmer]

 

This is purely for interest

I've just been "gassing" with a couple of friends and we were discussing the pro's and cons of using sealant with head gaskets the discussion was inconclusive so I thought I would ask here what general thoughts are.

We used to put a coating of red lead on some of the old tractor blocks prior to fitting gasket and cylinder head,

So over to you gents--well seal type of compound ?? We thought that it may well depend on type of gasket.

Mike

[DAVE BRADY]

Hi Mike, 

Apart from very early in my motorcycling life I have always used solid copper head gaskets.  Well annealed and without any sealant I have not had any problems.  I have read several threads re using sealant and they are generally inconclusive.  I think it is always worth getting the head checked for flatness when doing things like valves etc. and re-torquing the head bolts after few hundred miles.

Dave.

[Bess]

Hi,
    I have never used sealant unless the gasket manufacturer specifies differently.

The secret is getting the mating surfaces correct and clean, the right gasket, installing as per good engineering practices such as new studs/bolts of the correct length, threads and blind holes clean correct torque and sequence.

If the above is impossible and there is no other alternative I guess sealant would be used. There is a lot of cylinder heads with broken fins due to people breaking the sealed joint apart.

Best wishes...

[AdrianS]

I think a well annealed copper gasket should provide a good seal without any sealant.
My opinion re torquing a head: on my A50 it is virtually impossible to get accurate torque readings on the bolts and nuts when fitting the head . There is access to some of the fittings but some are virtually impossible to record an accurate torque figure ( the central bolt needed a very thinned down box spanner to fit and would probably split if I tried to torque it up too much) and the nuts in the head are guesswork. I would hate to tighten some of them up after a few hundred miles and then get some leakage due to inconsistent tightness of the head nuts and studs. Also, old studs and bolts have probably been pre stretched over the years so may not need re torquing like new bolts or studs need.

[DAVE BRADY]

Hi,

I agree that it is quite difficult to torque the nuts and the idea of a 90º angle between torque wrench and spanner is a bit awkward to hold but it is worth it. I do not know if there is a 'crow's foot' extension in the correct size.  The was a thread about this previously.  Re the centre bolt, a 3/8" drive socket is physically thiner and fits nicely.  I think that the re-torquing is more to do with the head gasket.  I would guess that the gasket can settle to some degree and that the previously tight nuts and bolt are fractionally less tight and that re-torquing is to ensure a more gas tight seal.  It would be interesting to know by how much an annealed copper gasket compresses by when torqued down.
The biggest pain on the A65 is having to remove the front rockers.

Dave.

[Bess]

Hi,
     Worth looking at service sheet 285 which offers a solution to correctly torqueing the head nuts. I cut a slot in a socket and welded it in the middle of a spanner which happed to be 6" long, so 3" to the ring or opened end.

The middle bolt on the A50 should be a reduced head, grinding or turning off some of the O/D from a good quality socket to fit the restricted space could be a solution.

Best wishes...

[Mike Farmer]

 

I have read all the posts with a great deal of interest. One thing comes to my mind regarding Torque Wrenches

I would imagine that for the earlier and greater part of my spannerring I didn't even know what a torque wrench was. I was possibly unaware that there were different types of spanner i.e. Whitworth AF BSF etc. and it all seems to have worked OK. Indeed I wonder how many of us still do it all by feel.
I certainely don't know if mine is any better for the use of these tools and of course there is no way of telling. I don't know if I was just lucky or in the majority but I certainly cant remember " re tightening" head bolts.

However we progress, learn?? and move on.

Mike
.

[Mike Farmer]

 

I've jut re-read the info on using a spanner on the end of a torque wrench. My thoughts are.as the fulcrum/break point is in the same place are we really extending the arm??? I dont think so but I shall be advised as usual.

Mike

[Calum]

I've jut re-read the info on using a spanner on the end of a torque wrench. My thoughts are.as the fulcrum/break point is in the same place are we really extending the arm??? I dont think so but I shall be advised as usual.

Mike

Yes, you are. To make it simple for the maths side though you must keep the spanner in line with the torque wrench - angles are doable but require a little more working out.
Now imagine it with spanner in line as one long lever. For a given torque, we all know that the further out from the centre you go the less force you need to apply. The bolt/nut is your new fulcrum point, where the torque wrench clicks doesn't really matter, but the reading on the wrench itself is only calibrated with the square drive over the fulcrum. With the centre of the turning moment now further away the setting will be lower.

[chaz]

you can use a torque wrench as long as you know how to use one.. I work with non  engineers that carry on pulling after the click and he wonders why he cant get on skilled money!!
As for BSA's Ive used the service sheet method since the first rebuild

[Mike Farmer]

 
Thanks gents.
 
I don't have a problem with the maths etc its simply the same as weight and balance however I have never used a torque wrench with an extension: - If in doubt, ask!!! The only dumb question is the one you don't ask and assume the answer.

Mike

[Mike Farmer]

 

This post is just to look at a couple of aspects floating through my mind.

Those of us with torque wrenches--- when did yours last have an accuracy test?. Mine?---never!!

My wrench is 18 inches long. My hand is 4.8 inches wide. For absolute accuracy where do I measure the moment? From the very end or midway across my hand--which would decrease the moment by 2.4 inches. What allowance do I make for the friction energy absorbed by the act of moving the bolt in the thread. ( I know that its negligible and as we aint building spaceships probably not too important)

I know these points have very little bearing on our day to day use but just thoughts.

Mike

[DAVE BRADY]

Hi Mike,

My torque wrench has never been re-calibrated but all the time I have had it I have probably only used on about 40 to 50 jobs.  Head bolts and nuts, clutch nuts, rotor nuts and the like.  If you are using it in a busy workshop then I would think that re-calibration would be good idea or just buy a new one every few years.  The moment is determined by the length handle but once set it would not make any difference as the 'click' indicates the correct torque has been applied.  If you choose to hold the wrench in a different place it will just mean that you will need to apply more or less force to get the 'click'.
If I remember correctly the torque figures are for clean and un-lubricated threads and the estimated and probably ideal friction will have been taken in to account.  Is not the friction created by the torque that keeps the bolt or nut tight?

Dave.

[Martin S]

Having done an automotive engineering apprenticeship I was always told categorically not to put sealant on head gaskets.
Having said that, I recently read on an American forum that it is useful to fit O rings in the 2 oil drain holes at the front of the gasket. I have done this on my A65, which has a solid copper gasket. Too early to say if it has made any difference yet, I haven't been able to put any miles on it since re-assembling; I'll report on it later in the year when I can get out on it. Hopefully soon.....   

[DAVE BRADY]

Hi,

I have put 'O' rings on my A65s recently.  I hadn't bothered before but noticed that any slight weep seemed to com from that front part of the gasket.  I did hear about the 'O'rings many years ago and assumed it was a BSA modification on later models.  However, there is no reference to them in a '71 manual and parts book.

Dave.