Repairing crankcases and counter bore machining

B

Brian Thompson

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Non-VOC Member
Hello,
Are the crankcases easily repaired? The Rapide "C' engine I have to overhaul has the timing chest side of the left centre main crankcase split. Accident damaged a long time ago. I don't have the engine at the moment , my friend was describing that set of cases too me on Sunday. Just wondering if there is anything special about the Aluminium used in the cases?
Just getting things organised in my mind, before I start.
I have ordered the 5 speed transmission from Quaife/John Surtees. Crankshaft next and associated bearings,gaskets and seals.
Does anyone know how much material needs to be removed from the counter bores when installing the 600 cc kits?
Thank you
brt650 :)
 
davidd

davidd

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VOC Member
brt650 said:
Hello,
Are the crankcases easily repaired? The Rapide "C' engine I have to overhaul has the timing chest side of the left centre main crankcase split. Accident damaged a long time ago. I don't have the engine at the moment , my friend was describing that set of cases too me on Sunday. Just wondering if there is anything special about the Aluminium used in the cases?
Just getting things organised in my mind, before I start.
I have ordered the 5 speed transmission from Quaife/John Surtees. Crankshaft next and associated bearings,gaskets and seals.
Does anyone know how much material needs to be removed from the counter bores when installing the 600 cc kits?
Thank you
brt650 :)
Click to expand...

I would not say that the cases are easily repaired, but in the hands of an excellent weldor they should not be a problem. He will also make the decision about material. Depending upon where the repair is, the cases may need machining in various areas to couteract any warping. Give him the case covers and screws so he can protect the surfaces and minimize warpage.

If you have to machine any surfaces after the welding, bring the new cylinders to the machinest for fitting. I am of the shcool that says the cylinder should slip in easily with no clamping effect from the cases. If the case clamps the cylinder to tightly, it will change the bore of the cylinder slightly, which is not good. There are probably other opinions on this issue which you will hear.

The 5 speed is nice, although I prefer four, but new gearboxes need a lot of fettling. You might want to try fitting the box the minute you get the cases back to see if there are any issues. There usually are. New parts are generally the way to go as the used ones often are worn enough to cause problems.

David
 
K

ksbundy

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VOC Member
Hello, The crankcases can be easily repaired by a competent welder. I ran a vincent on speedway that had repaired cases (both halves) where a conrod had passed through the back into the gearbox, without problems, I also have another set that I have had the repair from when a primary chain let go. Firstly I made up a mandrel to fit into the bearing journals with the cases bolted up tight. After the welding check to see if they are still true. One set of cases it worked another it didn't and I need to line bore the tunnels and fit a sleeve. I have worked on Frank Sinclair's old lightning and the drive side mainbearing on it had been repaired this way. Just a comment, the welder said that the alloy was very good quality and easy to weld (compared to other old british bikes).
All the best
KS
 
C

chankly bore

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If any of you blokes need to replace the generator mounting lug, drop me a note. The Victorian Section is used to repairing cinder chairs and has the casting available.Cheers!
 
greg brillus

greg brillus

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Hi there i have to agree with davidd on the fit of the liners into the crankcase, and see no reason for the liner to be a tight fit as there is little heat transfer down that end of the cylinders anyway. I have seen cases opened up to take the 600 kits and there seems to be very little room left at the inboard end of the cylinder hold down studs, but given the heads are only torqued to 30/32 ft/ lb's they should handle it ok. Be very hesitant to take others advice on pulling the heads to 45/50 ft/ lb's as some advise, as this will almost certainly distort the liners or worse. As another aside with regards to the 5 speed box, make sure that the bevel gear pt no:G39AS which needs refitting " Before" the cases are finally bolted together....has enough rotational travel to allow for the extra travel that the 5 speed camplate needs. The 5 speed camplate vs's the standard 4 speed plate has 6 detents around its circumference against the 4 speed's 5 detents including neutral of course, but the 5 speed plate has extra travel to pick up the extra gear....so to allow this to happen, the G39AS bevel gear needs extra travel to allow the camplate more rotation....there is a lot more info required to replace the 4 to a 5 speed, but hopefully this info will be supplied with your 5 speed kit....cheers for now....Greg.
 
B

Brian Thompson

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Non-VOC Member
Excellent advice thank you.
I need to find a machine shop that's for sure. I don't need a failure.
I'll do that engine next and concentrate on the "B" engine first. The four speed has been modified for racing. My friend believes it won't be user friendly for the street. This engine has 2 front heads, was overhauled in the 70's and hasn't been run since. I'll strip it and see what it needs. Also it apparently has a twin scroll oil pump drive. Is this a common mod?
Thank you again for your help and thought's.
Cheers
brt650
 
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