John's KTT Repair

Some of you may know that John Goodall has had a bit of trouble with cracks around a main bearing housing in the crankcase of his wonderful Velocette KTT.  He has recently sent me the email message below that you might find interesting.  Some photographs of the problem are below the email.

Dear Eddy,

I have got the 1930 Mk1 KTT back together now after some good advice from my room mate Bob Higgs. A little conclusion is as follows:-

Talking to my friend and mentor Bob Higgs last December about the difficulty of successfully welding the cracks in the KTT crank case, we both realised it was fraught with problems especially as the castings are from at the latest 1930 and are now well over 87 years old. Any porosity and existing cracks would be oil infused with a deleterious effect on welding not to mention the possibility of silicon in the alloy which would complicating this.

So some alternative was desirable certainly in the short term with no new castings for the crank cases available. Bob suggested fitting an oversize bearing in the cracked timing side making a dummy bearing exactly 0.002 thousanths of an inch oversize, dropping it in to the heated cases and see what happens on cooling. All seemed to get no worse and as Bob said what is the worst that can happen, maybe the crack gets worse, or maybe not? It visibly got no worse after the experiment and so a new 0.002”oversize bearing fortunately in stock at our own Phil Haywood’s Vintage Bearings sorted the bottom end.
I had already had the barrel re bored by Graham Rhodes and his father Ivan sold my a 0.020” oversize Mk2 KSS piston which I machined to suit. The Mk2 piston needs a radius machined on the piston crown to clear the head contours of the earlier engine. This produces a squish effect which might be advantageous too?  It should be noted that oversize pistons are not available for most racing engines as this would place them outside the capacity limit. So if you want a new bore it usually means new cylinders and pistons are required. A new exhaust valve and guide were also fitted and the whole engine rebuilt, making a better job of setting the bottom bevels this time as well, so no whine is detectable now.

The engine fired first kick and started on the fourth sounding good with no smoke. All that is needed now is to get it hot and re-set the oil pressure due to a rebuilt oil pump being fitted as another needed improvement. Time will tell if all of this is a short lived, or slightly longer term solution? I wonder what Titch Allen would have done? John Goodall.

My reply:

Dear John,
We all love a story with a happy ending.
I think that as Bob said, what have you got to lose. With a bit of luck you and the KTT should be good for quite a few more enjoyable rides.
I spent quite a lot of time with Titch and I think he would have been thrilled to bits to see your KTT back together with what he would have classed as a "super bodge".
Would it be OK to put your email on the website as it is an interesting little read?