G11 Crankshaft HELP!

Tenshi · Post by **Tenshi** » Thu Aug 18, 2005 1:53 pm

Hi to all...What are your thoughts on how far crank journals can be safely ground? Have been told not to grind to more than .030". Also, building up journals by metal spraying..Good idea or bad idea, pro's and con's? {regarding Matchless 600} Have '56 G11 restioration to do and need advice on which way to go...Thanks Waiting with baited breath

lawrence · Post by **lawrence** » Thu Aug 18, 2005 11:48 pm

Hi Mark
I believe the owners club stock +40thou shells now (check!) so I guess this is safe.THE MOST IMPORTANT THING TO CHECK IS THE RADII. Metal spraying if done properly should be fine but if your radii are wrong from this or a previous regrind the shaft will break with disastrous consequences. I know. [:(]

Tenshi · Post by **Tenshi** » Fri Aug 19, 2005 2:06 pm

G'day Lawrence...Thanks a lot for your reply. I've read of so many crank failures in this forum that I guess I am a bit apprehensive about going the wrong way as far as the crank is concerned.
I'd be interested to know how you've gone with your machine since your bad fortune with it. Thanks again Mark Berney.

paul knapp · Post by **paul knapp** » Fri Aug 19, 2005 3:29 pm

Hello mark, while you are investigating metal spraying, also ask a few questions regarding having the journal hard chromed and ground. I once worked in an engineering firm who specialised repairing crank journals by plating. There is no heat involved and no roughing up of the surface to be repaired, (to allow the spray to bond, only a lick to true up on the grinder before plating) virtually eliminating any sharp corners made by the premachining, where a fatigue crack can start. It is extremely hard, from memory about 68 plus Rockwell "C", a lot harder than spraying. The blending radii is critical and details are given in F.Neil's workshop manual. I could send you a copy on this contraption if you want to go that way. A good plater will probably recommend a stint in the OVEN afterwards to eliminate any hydrogen embrittlement which may occur.
See yer mate.

Biscuit · Post by **Biscuit** » Fri Aug 19, 2005 6:12 pm

Come on Lawrence, -40 thou. I have seen cranks advertised as -60, never had experience of this though, all mine are standard .... for the moment!

CR · Post by CR » Fri Aug 19, 2005 6:14 pm

About 7 years ago I reground my '63 31CSR crank to -0.080" and used slightly modified Mini Cooper shells (simply reduce the width and transpose the locating 'tang' to the opposite end - BMC Mini 850/1000cc crank journals are same dia. as AMC twins). In the past this was a popular pastime as Cooper shells were generally regarded as better quality than the stock AMC and 'pattern' shells that followed.
Both Steve Wilson and Frank Westworth have caned this machine during magazine tests, but probably not as much as I have over the years. I occasionaly still run it up to 80+mph on the A39 'Atlantic Highway' down here in Cornwall...and hold it there for mile after mile (but only after the caravans have all headed for home at the end of the holiday season).
I've run this machine on Duckhams 20/50 since the regrind (high capacity pump) and changed the oil and filter every 1000 miles max. Seven years on and about 19,000 miles and she's still sound, but then the engineering firm I used to do the job knew their stuff with AMC cranks.
The secret of success with AMC cranks as far as I'm concerned is meticulous engineering practice and assembly, sound dynamic balancing and VERY careful positioning (centralising) of the centre web.
I'm not suggesting that anybody should follow my example. I only relate my experience to demonstrate that (a) AMC cranks can sucessfully be ground beyond -0.040" and (b) they are not at all fragile if handled with a modicum of good engineering practice.

lawrence · Post by **lawrence** » Sat Aug 20, 2005 12:21 am

Dang ma britches and spank me with a paddle! Alan, as always, is correct. Jampot Spares sell +60 thou shells. I should have got off my but and gone to look in the spares list but in my defence it is in the shed at the bottom of the garden and it was raining and I didn’t want to spoil my new hairdo and I had just polished my shoes and anyway the wife had locked up for the night so it clearly wasn’t my fault. In fact thinking about it, it was obviously my wife’s fault unless she reads this in which case it was the cat to blame. Well, I didn’t want to wake the poor moggy up, she is old, deaf and blind. One day we will all be like that so should not be too hard on her. Shame on you Alan picking on a defenceless animal! (The cat, not me).

Mark. My bike has done 420miles since fitting the new crank and she feels lovely, much better than before. I tried centralising the web as a lot of people have said it makes a difference. I guess it depends on the machine as it made no difference to mine. What I did find though was once I had the crankcase halves together, I dropped all the bolts in loosely and there was surprisingly still a lot of movement (twist) in the cases. I twisted the halves until I found the point where the crank and camshafts rotated most freely then tightened the appropriate bolts. It does seem to have made a big difference and the engine turns far easier than before. As Chris says I had the crank balanced. This is a must. Last time it was done dynamically but on an older balancer. This time it was done by T&L (see Jampot ad) on the latest whiz-bang balancing machine and the difference is startling. For the first 100 miles I kept thinking something was wrong as it felt so different than before then I realised it was the lack of vibration. It is silky smooth. It hasn’t been over 40mph yet so that may change but it feels much better and no bulbs have blown, nothing has broken or come loose. Whether I will be able to keep it under 80 when it is run in is another matter. It just runs away with me, officer, honest!

I fitted a Rik Gibbon oil pump and head gasket and studs set which all seem marvellous. Worth the head set for the raised nuts which make torquing the head a doddle and stop them rusting to the studs so much. And did I mention THE MOST IMPORTANT THING TO CHECK IS THE RADII!!!!!!

Lawrence [}:)]

Tenshi · Post by **Tenshi** » Wed Sep 07, 2005 11:57 am

Thanks for the help guys..I have purchased a crank from the U.S.A which has been sprayed back to standard from .030" and used successfully and now needs to be ground to .010" so methinks this will be O.K. I still have my original crank so when the other arrives I'll decide which way to go. You have all been a great help..Thank you very much Regards Mark Berney. Ride Safely