Can bodging be justified?
I’d just been for a twenty mile run through the lanes on my ’57 Brum Scott and when I got back home there was a dirty oily streak running down the front right hand side of the crankcase coming from the exhaust manifold. I checked the flange bolts and found that the R/H one was loose. I tried to tighten it but it just went round and round, obviously the thread had stripped. The bolt was OK and so it must be the thread in the cylinder block. I had acquired the block a couple of years ago, and when fitted all appeared to be well.
I didn’t want the hassle of lifting the block to heli-coil it because it would have meant taking off the tank, radiator, distributor, dynamo etc., and it can’t be done in situ because the frame down tube is in the way.
I could have tried to turn up an oversize bolt but decided instead to try a bodge.
I drilled a 3/32″ hole down the centre of the bolt and then, using a junior hacksaw, cut down the length of the bolt almost as far as the head. I then tapped a 3/16″ length of 1/8″ rod half way down the drilled hole. This spread the bolt and so I squeezed up the open end until it was it’s original diameter and ended up with a barrel shaped bolt.
When screwed back into the block it held beautifully and tightened up well.
That will hold, I hope, until I next lift the block and do the job properly!
it seems you may have already fixed it! But, it may come loose with the heat cycling and vibration. Another method I’ve used for such temp fixes is as follows:
Take the bolt and drill down from the head end to within 1/8″ of the bolt end, in effect creating a hollow bolt from the head end. Now tap this a suitable size, in your case perhaps 3/32″ or 1/8″, or M3 for the young guns. Now cut a slot into the bolt as you have done from the threaded end to 3/4 the way to the head clamping face.
Wind the bolt into the hole as far as it will go and it has a slight grip, now wind a second bolt or grub screw down the centre of the first bolt. This will seat into the drill point / thread blind end and spread the bolt from the bottom into the hole. You can tweak the outer bolt tighter as you tighten the grub screw, and this method does not risk cracking the casting as you cannot put too much pressure on it, and it will come out easily by loosening the grub screw.
If you current fix works then leave it, otherwise perhaps try the above, either are easier than stripping half the bike!
Your method is a more elegant solution (more of an engineering fix than my bodge) and is one that I will probably use in the future should the need arise. We’ll see how long mine holds up before trying your method.
I’m sure your’s will last a while, I’ve told myself about fixing things properly that are still running on my bikes today, on the “to do” list. Its just the barrels are made from grey iron and it is brittle (and soft) so you have to be careful winding tight bolts into holes or it may crack. I’ve done this on a head stud last year but luckily it was one of the centre ones so had a decent area around it to seal. It is still together and still water tight today thanks to some good sealer but really I need to take it apart and weld it. Over winter… maybe….
Confuscius he say “Nothing so permanent as the temporary”
Another way to approach this problem is to see if there are any “unused” threads left in the bottom of the threaded hole in the block, ie. you may be able to use a longer bolt….Check the depth of the hole and compare that distance with the amount of bolt that projects beyond the exhaust flange and gasket. Get a new bolt and cut it to the maximum possible length, but of course ensure that it cannot “bottom” in the hole. Also ensure that there is no debris in the bottom of the hole. There is often a surprising amount! Whilst on the subject, next time you have the barrel off also check that the threaded holes for the cylinder holding-down bolts are also thoroughly cleaned out, as they also seem to accumulate debris. Yet another approach, ie. bodge, if you have a set of adjustable split dies, is to make a new bolt that is “fat on the threads”, ie. a bit oversize, but don’t overdo it as if too tight it could crack the cast iron if forced in. Make sure that it can be screwed in without resorting to much more than fingers!
I do it all the time Dave! Some times unsuccessfully!!!!! See my wanted ad in this forum. Regards Ted 😛
Did that, and no there wasn’t, even after cleaning our the debris. Thought about making up an oversize bolt but decided an expanded bolt was easier and quicker plus it worked!