Blinking twin head gaskets!

[Eric]

Lawrence I assume you know that in later engines the stud diameter was increased to 3/8" dia presumably to allow more clamping force to be applied with higher torque levels. Its not a particularly difficult job to do and could (I think) be done with the engine in situe if you are brave enough. The heads and cylinders would have to be removed and these would also have to modified by opening up the holes but they can be done in the workshop. Ensure there is no possibility of anything dropping down into the crankcase with masses of rag stuffed in everywhere, drill out the existing crankcase holes to tapping size for 3/8" BSF there would not be much metal to come out. Then re-tap to 3/8" BSF start with something like a second tap (Slight Taper) finish with a bottoming tap to get full thread almost to the bottom of the holes. Apologies to Alan if my terminolodgy is wrong its a long long time since I was a hands on engineer.

[Biscuit]

I fail to see why a stud could accept 18ft/llbs in 1956 but not in 1957!!!!!!!. If going the 3/8" stud route, I would use 3/8" Whit. and secure an extension to the tap such that you can tap the hole with the barrel in situ, thus ensuring that the hole is tapped square. It only needs a minor variation and it is extremely difficult to get the barrels over the studs. Bottoming = plug and vice versa.

[Eric]

Alan in one way I would agree with you about using Whitworth even hands off engineers know you should use very coarse threads in Aluminium. But as stripping of the 5/16" BSf in the crankcase is not a great problem but breaking the studs is, the gain in cross section area made by going up to 3/8" would be somewhat reduced by using Whitworth threads, I will work it out later. The idea of using the barrels as a guide while tapping is excellent with an extension made for the job it could be very precise indeed. Once did something similar when a hands on engineer helped me to get a broken crankcase throat bolt out. He made a bush to fit the hole and guide the smaller drill we used to make a hole in the broken bolt to use for an extractor. The extractor was a tapered square with sharp corners formed on some tough square steel. Put into the drilled hole and firmly tapped to key into the stub of the bolt. Not so hard that the bolt would spread out but enough to bite, then using a tap wrench on the other end that was squared the broken bolt was just screwed out well done Dave.

[lawrence]

Alan
Tried your suggestion of torquing the bolts then releasing them and re-torquing to see if they tightened any further. It made no difference at all but, thinking about it, that is almost certainly because the studs/nuts are clean and have been torqued up very frequently, at least weekly. I think it would make a difference if the studs were ‘aged’ and had not been torqued for a while.

Following that test I popped off the nearside head gasket as well which was completely and impressively blown at the narrow section even more so than the offside. Neither gasket looked as if it had been squeezed by the head/barrel so I have followed your suggestion and torqued them up to 18lb/ft. They seemed ok with it and I figure with current legislation I can probably sue you for a zillion pounds for the thread stripping and subsequent emotional damage incurred (ONLY JOKING!!!). If that doesn’t work I will try making or buying some solid copper gaskets. Hope I don’t end up getting inserts in all the crankcase threads just so I can get more torque on the heads.[:(]

I hope not to find out why they reduced the torque settings[xx(]


Lawrence [}:)]

[Eric]

Lawrence I dont think the problem is that you strip the threads in the crankcase although I know this can happen, its because you shear the studs. I did the sums assume you have the same material then 3/8" dia with BSF will be 49% stronger than 5/16" with BSF while 3/8" dia with BSW will be 33% stronger than 5/16" with BSF. This of course is because the BSW thread is deeper than BSF perhaps the thing to do if change to 3/8" is considered is use inserts from the word go when changing the holes (If there is enough metal to do it) and get some high tensile studs made. I will ask someone who I know who has had the same problem as you what he did in the end to overcome his problem that occured many times in the early days of his re-build.

[Eric]

Just a thought have you cheked that everything is flat where it should be and that the the gasket can get compressed correctly or is it possible that someone has been messing around in the past maching away parts that they should not have changed.

[Eric]

I have spoken to the guy who has blown more head gaskets then he has hot dinners and the news is not good. He has changed to 3/8" dia high tensile studs and torques down to 30 ft lb. Following a re-build he will copper grease the threads and torque down every 25 miles without slackening first and he keeps doing this until they will not move any more. After that he checks every few hundred miles just in case. He can and does still blow the occasional gasket. He thinks the biggest improvemnt was when he had the heads skimmed to make sure they were completly flat. He has in the past tried just about everything including copper gaskets, but these always leaked oil and he thinks there is a problem of some sort if trying to use copper with "O" rings and 3/8 studs but I could not fully understand what he meant without a head to look at. It has to be siad he does ride his bike very hard and he has come to accept there is not really a cure with only four studs. By the way when he fits the studs he ensures they bottom in the holes leaving at least a full thread showing above the crankcase and he uses locktite to keep them there.

[TommoT]

Some people use a sealant of some kind applied to both sides of a solid copper gasket. Aluminium spray like that used for welding. Trade names like Honda Bond and Permatex liquid gasket spring to mind. A friend of mine uses this on his 650 and combined with the proper torque down sequence and the occasional re-torquing this seems to keep the problem under control.

It would also be worthwhile to make sure the engine runs as cool as possible, without being too cool that is! Ensure that the mixture is not too lean. Make sure the exhaust is not too restrictive as this will increase temperature in the entire exhaust line.

Good luck and lets hear how it goes (which we undoubtedly will!)

Regards,

[Eric]

Tom any idea wich Honda Bond? There are I think several different variations with with a number e.g. Honda Bond 3. When a head gasket went on my car I let the garage fix it. They told be they used an anerobic gasket sealant in addition to the normal head gasket. These sealants only cure when all air is excluded does anyone know much about these?

[lawrence]

quote:Originally posted by Eric Brooker

Just a thought have you cheked that everything is flat where it should be and that the the gasket can get compressed correctly or is it possible that someone has been messing around in the past maching away parts that they should not have changed.




Tarnation! Now I have reassembled it all and am just waiting for the exhaust to dry I read this post. you are right Eric, I checked all the surfaces were level but never thought to sit the head on the barrel without a gasket to see the fit. Ah well, guess that will be the first thing to check next time [:(]

Lawrence [}:)]