Author Topic: Metal Spraying Crankshaft query ?  (Read 6694 times)

Offline Stephen Foster

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Metal Spraying Crankshaft query ?
« on: 09.09. 2012 18:25 »
As I have a spare small journal crank lying around Im considering having it reconditioned in the above manner . My questions are

1/ Is the crank integrity compromised ?
2/ Is this very expensive ?
3/ Can Anyone reccomend a specialist , especially in North West Lancashire (not essential) ?

Thanks in advance ,

Steve ...
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I own a 1955/56 B.S.A Swinging Arm "Golden Flash" , had it since 1976 .

Offline mark

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Re: Metal Spraying Crankshaft query ?
« Reply #1 on: 10.09. 2012 06:26 »
Steve, I had a crank with one journal that had been metal sprayed by a previous owner, I had it reground and nitrided as part of the rebuild. It lasted 10 miles before the surface broke up.

Mark
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Offline duTch

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Re: Metal Spraying Crankshaft query ?
« Reply #2 on: 10.09. 2012 09:22 »

 Hi Steve,
              I asked about this recently at the hard-chrome place, and the response was not encouraging, maybe ok for concentric rotation, but for 'reciprocating rotation', like on a crank, he said the loading would shred it, basically as Mark says.
  I know it's been around for a while, and probably ok in certain circumstance, but others will maybe have a more conclusive idea,
       Cheers, duTch
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Re: Metal Spraying Crankshaft query ?
« Reply #3 on: 10.09. 2012 16:43 »
I don't know Steve, but I know that T&L Engineering in Beds, UK, has been spraying/grinding a steady stream of m/cycle cranks (big-end journals included) for a while with, they say, good results. I haven't had one built-up by them myself, but you could maybe give them a call to discuss the pros and cons as they're always very helpful and do good work at fair prices (01234 352418)? Very motor-cycle friendly - they have the crank from my A there right now (among other things), for a spray/grind of the drive side shaft to get (among more other things) the inner race of the main to fit properly.
I did have some big-ends sprayed once elsewhere, 30-odd years ago - the crank broke soon after and rather put me off. But I don't know whether that tells us anything useful today. Also, it was a very tired item, already ground to -80 thou on the ends and worn down best part of another 5 thou.
Good luck, Bill
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Offline Stephen Foster

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Re: Metal Spraying Crankshaft query ?
« Reply #4 on: 10.09. 2012 16:50 »
Thanks all for the input .
Fair to say the jury is still out then ?
Doesnt sound encouraging at all .

I shall speak T & L , Bill ..Thank You for the heads up .

Steve...
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Online metalflake11

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Re: Metal Spraying Crankshaft query ?
« Reply #5 on: 10.09. 2012 17:10 »
S.R.M. Engineering will tell you all you need to know. There are two methods for doing the job and one is better than the other. Give 'em a ring!
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Online bsa-bill

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Re: Metal Spraying Crankshaft query ?
« Reply #6 on: 10.09. 2012 17:33 »
the shop I use for rebores, regrinds and so forth also said it was not an option, if you find someone who reckons it's ok get a written warranty before you go ahead
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Offline Stephen Foster

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Re: Metal Spraying Crankshaft query ?
« Reply #7 on: 10.09. 2012 17:34 »
Thanks "Metalflake11" , sounds as though You have experience in this process ?

Steve...
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Re: Metal Spraying Crankshaft query ?
« Reply #8 on: 10.09. 2012 20:52 »
No, but I was at SRM on Friday and it came up in conversation. I have no attachment to them other than tens of thousands of trouble free miles over many years, and I rate their opinions to be up there with the best. One thing is for sure though, and that is they won't waste your time or money.

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Offline alanp

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Re: Metal Spraying Crankshaft query ?
« Reply #9 on: 11.09. 2012 14:45 »
I support SRM on this one. I had a crank where the drive side bearing had eaten its way into the journal and the end face of the crank such that the bearing could be thrown on from 100 yards.
They sorted it for me and I recently had the opportunity to take a look (after maybe 3000 miles of high speed thrashing) while the engine was apart and all was in order.
Answer : Give it to SRM.
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Re: Metal Spraying Crankshaft query ?
« Reply #10 on: 12.09. 2012 10:30 »
I know you said this is a "spare", but given that this is a small journal crank, would it not be cheaper to source a good second hand replacement rather than go to the expense and risk [however small] of metal spraying? SJ cranks are much cheaper than LJ cranks so it might not be viable. What was the cost by the way?

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Offline Goldy

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Re: Metal Spraying Crankshaft query ?
« Reply #11 on: 12.09. 2012 10:36 »
I had my crank metal sprayed Through RJ Motorcycles in Coalville and have since done nearly 3,000 miles with no problems. I would say its like anything it has to be done properly.
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Offline Stephen Foster

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Re: Metal Spraying Crankshaft query ?
« Reply #12 on: 12.09. 2012 12:20 »
I know you said this is a "spare", but given that this is a small journal crank, would it not be cheaper to source a good second hand replacement rather than go to the expense and risk [however small] of metal spraying? SJ cranks are much cheaper than LJ cranks so it might not be viable. What was the cost by the way?



It cost Me nothing .
I inherited crankases, g/boxes ,timing covers , forks , etc, etc 30 Years ago at least .
Agree It would probably be cheaper to buy a freshly ground crank as it is only spare & the one in the "Flash" has only had its first grind .

Thanks for the advice ,

Steve ..
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Re: Metal Spraying Crankshaft query ?
« Reply #13 on: 20.09. 2012 22:31 »
May I revisit, FWIW, this Q of metal spraying of journals, big ends in particular?

Last week the drive side mainshaft of my A was sprayed and ground to size to give an interference fit for the inner race, and at the same time the thrust face on the outer side of the crank web was built up to compensate for wear caused by the inner race's having spun at some point on the shaft and damaged but not broken (luckily) the shims. Crank end float was north of 20 thou but the engine was running perfectly when I decided to take it apart. In fact it had done 300 km the day before I grasped the nettle (August 16th) and decided to have a look, just because I felt a look was overdue.

The work was done by my favourite engine shop, T&L Engineeering (with whom I have no connection apart from as a regular customer for awkward jobs I can't do myself). The net of it was that after their careful ministrations and measurement there is now no need of any shimming of the bearing, the race is a modest interference fit as it should be, and the end float is exactly 2 thou. This job cost £109 excluding bearing and seal. Other jobs done to get the crankcases back to 'good as new' cost somewhat more, but it was interesting that even after 50K+ km in my hands, and who knows how many km before I got the thing as a dirt cheap unknown bitza beesa, the timing side bush and journal were still round and excellent at max 1.5 thou, and the big ends were unworn on -30 and really didn't even need new shells. All in all, testimony to religious 1000 mile oil changes I suppose - and more controversially a tribute to modern multigrades. No oil filter, no air filter, no mods at all, just a standard iron head large journal thick flange flat-top piston GF spec engine which has been treated semi-kindly most of the time, but has had very little attention in years.

In a long discussion about metal spraying, I raised again the question of building up cranks, especially big ends. This was something I had previously talked to them about in relation to a very tired 650 AMC crank from a defunct engine from one of my other bikes which I am raising from the dead. T&L would have been happy to spray it back to standard had it been necessary (in fact it took a grind to -60) as the radii were still there, and they say they have done a steady stream of these awkward and hard to find three bearing cranks over the years. Loads on big ends (as opposed to things that rotate concentrically) don't seem to be part of their equation.
They have built up 'thousands' of m/cycle cranks, almost always including big ends, and have had only one known failure, where an oil pump problem caused instant death. They say that they won't go more than 100 thou down on standard to get to a good starting point, and that there have to be no signs of lack of structural integrity. If those things are OK, they say that with a thin layer of molybdenum properly applied first as a base / key, and cast iron (or whatever is required) applied afterwards, there should be no problem. Technology advances have helped, they say, but the number one thing is the skill of the person on the tools.

The critical path is engineering expertise not marque knowledge, and I have to say that I will only ever send any of my engines to these folk for tricky repairs, even though it's a long way from France where I live. Were I in the position of needing to salvage a crank I couldn't replace more cheaply, then I'd have no hesitation at all in going there for advice and, probably, a solution. This week they have replaced a set of valve seats, and welded up and skimmed true a pair of AMC cylinder heads with gouges on the mating surfaces etc etc, all at a fair price, quickly, and well.

I take these guys at their word, so my 30 year old experience of disaster mentioned somewhere above is, I am now pretty sure, unrepresentative of what is possible in the right hands today.

Cheers, Bill
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Re: Metal Spraying Crankshaft query ?
« Reply #14 on: 20.09. 2012 22:44 »
Another option for the big end journals is hard chrome build up and ground to size.
I assembled a Domi 88SS engine for a friend who had this done on the recommendation from an engine reconditioner.
The engine has yet to be started but we are hopeful.
Should be OK for the timing side main on the A7/10.

Trev.
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