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MG Midget and Sprite Technical - Crankshaft Regrind Sizes
|HI everyone, My first post as any questions I have had have already been answered on the forum but I cannot seem to find anything on this particular query. I am restoring a Frogeye and as a break from continuous bodywork repair I have started the engine rebuild. The car has been in the garage for about 30 years and I stupidly stripped it down in my younger days although carefully putting the engine parts away in large plastic boxes. The garage got flooded years ago and when I retrieved them several years ago the crankshaft, camshaft were pretty rusty. I am now embarking on it as a retirement project. The engine now has had new liners fitted to the standard size, the head has been converted to unleaded and the crankshaft has been reground to -60 both main and big ends, the engineering shop did supply me with oversize bearings to suit but I cannot see any reference to taking the main bearings getting reground down this far, The car when rebuilt will not be raced or thrashed around but is this acceptable
|G F Smith|
|Hi Graham - assuming it is you?|
I too would have been a bit surprised about a crank grind as much as 60 thou. But looking on suppliers' online sales site I see that 60 thou bearing shells are commonly available, so perhaps its not so unusual after all.
Before this latest regrind, had the crank been ground before or was the needed amount all as a result of the rust damage?
Did you go for a balanced crank & flywheel whilst you had the chance? I think its well worth doing.
|Thanks for the quick response Guy and it is Graham. I omitted to say it was a 948 gold seal engine and I do not think the crankshaft had been reground before it was all down to the rust damage. I haven't went for the balanced crank/flywheel yet but it seems an idea. I am waiting to what the responses on the forum are before deciding to proceed or fit another crankshaft.|
|G F Smith|
|I think .060" is 'normally' as far as you would go, in fact there is currently a midget EN40 crank on eBay, which is .060/.060", although it is being advertised as being for an MGB.|
|Dave O'Neill 2|
|An EN40 crank at .060/.060" seems to be an oxymoron. An EN40 would be great for a performance engine but at .060 over? Better to spray weld.|
|The crank is .060" UNDER, not over.|
|If its at .60 id look into having it pinged nitrated and (turfied ?...is that the word im searching for)|
Its a hardening process
|Prop and the|
What have you got to lose? Assuming the engine is cleaned and assembled properly it will give thousands of miles service. Cheaper than buying a new crank. I once had to have a Sprite crank re-ground 60 thou for a second time as, when first ground, swarf had been left in and wrecked a big end. It was making a lot of noise when it failed going up the M6 to the lake district. Friend towed it home the day after. Long time ago.
The word is Tuftrided... but the process does often lead to crank warping which has to be corrected by regrinding
the journals and there is no room left to do that at - 60.
If you do use it then definitely have it balanced. Personally I wouldn't sell a reconned engine with smaller than -30 and would look for another crank, especially if you are going to do any sort of tuning to increase power.
|Chris at Octarine Services|
I was thinking pistons, brain fart. Getting older not sharper.
|The problems I had 'in days of old' with the 948 cranks were only when I revd them too high ! - snapped a couple !|
Red cranks were virually unobtainable and very expensive.
Mine were not balanced (not available in local area and limited cash !)- plentiful supply in the breakers yards in those days ! often wondered if a harmonic balancer would have helped.
I would keep the revs to about 5500 and expect it to run well.
This thread was discussed between 17/03/2017 and 18/03/2017
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.