Scotsman with a cracked head (and other issues)

[† Norrie]

Greetings from Bonnie Scotland 

I have been making progress with my R25/3 and now have a rolling chassis with tidied up cycle parts - it looks good and I feel I am now getting some where which is great especially if there are to be visitors to the southern part of the UK during the summer of 2016. It would be good to visit on a single cylinder rather than on a twin. 

Initially it looked like a previous owner had swung down from the trees to work on this engine but I am hopeful all is recoverable with time, money and effort. I have a spare crankcase and bottom end and will combine the best of both to produce a reliable motor. The big end needs replaced and I will organise a local engineering company (Brown Brothers in Edinburgh: http://www.georgebrown.co.uk/category/auto-engineering) to do this and balance the crank. This company also offer aluminium welding and I wondered if repairing this crack between the steel spark plug insert and the exhaust valve was a reasonable proposition? Is this a repair that people have done or is there a real risk that something fails and falls into the cylinder which would be extremely messy? I imagine the spark plug insert and valve seat would be removed and renewed after the repair.
   

Best wishes

Norrie

[† Norrie]

[RolfD]

Hi Norrie,
I had the same head Problem at my first R27.
There was an oppotunity to let it beeing welded at some special mechanic who knows about the material and has the skills to work out on that.
But at last i decided to get me a used head, at that time some years ago there was some chance to get some for affordable prices.
Well, but I recognized that there must be some people here using a welded head because that kind of phenomen is not very rare to be seen.
Good luck to get further with your project!
Best Regards
Rolf III

[4Taktix]

... Is this a repair that people have done or is there a real risk that something fails and falls into the cylinder which would be extremely messy? I imagine the spark plug insert and valve seat would be removed and renewed after the repair.

Hello Norrie, yes, this is a nearly common damage and can be repaired by welding, if the shop has someone with the required skills.
The crack has to be grinded or drilled down to the base, until only stable, firm aluminum is left. ( thread-insert and valveseats to be removed)
Then the complete head has to be heated up slow and evenly, before it can be welded thoroughly.
Without heating up to an appropriate temperature you have a high risk of bringing in high tension by the welding and  causing further potential cracks
and warping.
It would be a good sign if the shop is experienced in welding big aluminum parts with thick diameters, e.g. engine-housings or similar.
The Webpage of george brown looks as if they do ;-)
I had my head in a shop, which repaired rare ship-engine-cases from all over europe and an according reputation.
No troubles so far. ( ~ 8000 km since the repair )
Good luck and best regards,
Sascha

[Kurt in S.A.]

Cracks just like this were common the twins.  Duane Ausherman discusses it here...towards the bottom he discusses the historical background.  It seems the cracks were not a huge problem and people continued on.  I admit it would be hard to run with this kind of damage.  I suppose if it weren't leaking compression, maybe it is stable??

http://www.w6rec.com/duane/bmw/head/

Kurt

[† Norrie]

Hi Rolf III, Sascha & Kurt

Many thanks for all your advice. I am one of those pernickety folk (quite often a curse) that would be unhappy to ride with the crack where there is a chance it could be repaired. I would hate having finally finished the machine to have it lose the valve seat as I was flying along the road. I will take advice from George Brown & Co as I don't need to make an immediate decision as the bottom end and gearbox still need looking at. It will be a while before the head goes back on.

Very interesting tales Kurt, from mechanic Duane Ausherman during the early 1960's. 'Butterheads' and yet they have such a good reputation for build quality and reliability here in the UK.

Best wishes to all



Norrie