Turning a finned aluminium cylinder barrel for a motorcycle

Hi All, I have just joined this forum; I have several engineering interests inluding classic motorcycles, and I would be very grateful for your accumulated wisdom. I have a Myford Super 7 at home, and access to a Harrison lathe at Tech College. I want to make an aluminium cylinder barrel for a Matchless motorcycle, which will require cutting fins about 2.5 ins deep in a 9 in diameter alloy billet. The College only has HSS parting off tools which will not cut deep enough, and the indexable tip tool I use on the Myford is not strong or deep enough. I am prepared to buy a suitable parting off tool to use at college, preferably with a rounded tip to cut the bottom of the fins nicely. Any suggestions/sources, bearing in mind I will only use the tool for this one job? My plan of action is to bore the cylinder on a Bridgeport using a boring head (it is off centre so doing this job on a lathe would be very hard). I would them mount the barrel on the faceplet and use a plug in the outer end of the barrel bore to support it with a rotating centre, then cut the fins. Finally I would finish the square base on the Bridgeport and insert a cast iron liner. Any thoughts/ideas/am I biting off more than I can chew? Term starts nin September so I would have plenty of time to get materials. Grateful for any help. Andrew

Hello Andrew

I'm sure others can give a more complete answer but I'm happy to share my slightly similar experiences with you. Several years ago I was asked to make a pattern set to replicate a GWR carriage warming radiator. These are essentially a cast iron tube with deep fins attached. I.e. not too dis-similar to an air cooled motorcyle cylinder, but much longer. To produce a robust pattern my original intention was to take an aluminium billet and machine the fins in much the same fashion to your intention.

Long story short. After several broken tools I changed my tack and eventually made the pattern using Sikabock resin with the side of each fin produced by setting the top-slide almost parallel with the cross-slide to produce the draft. As you are intending to subsequently fit a cast iron liner have you considered making a pattern and getting the outer part of the cylinder cast at a local aluminium foundry?

Of course some manufacturers would cast the iron liner into the aluminium finned outer portion, presumably to improve heat transfer.

Edited By Brian Oldford on 02/04/2017 10:55:47

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How wide are the 2 1/2" deep slots.?

Nick

The fins on the GWR carriage warming radiator pattern are at 1/2" centres (plus contraction). I guess similar to those on a m/c cylinder.

Edited By Brian Oldford on 02/04/2017 11:27:23

Cylinder on a rotary table and use a slitting saw in the mill?

HOW?? Melting point iron 1500C, melting point Aluminium 660C

It was done the other way round ... ally cast onto the other bit.

Wellworthy Alfin process IIRC. Velocette etc. ???

D.

Ha ha! I understand you confusion. I meant the cylinder is cast-in.

I was not confused, just thought it was worth a correction.

I think I would use a straight ended parting tool that takes the MGMN type inserts as they offer a bit more support than the plain bladed ones for most of the cut and then switch to either a MRMN round ended insert though you will have a job finding a holder that will part that deep unless you also have deep pockets

Or make a custom tool from say 50x6 mild steel held on edge with a 6mm RCGT to the end, if you look through KWIL's album he has something similar for machining large crank shafts

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And a nice rigid lathe and set up preferably pumping the correct flood coolant.

Nick

Modern motorcycle cylinders are all aluminium and the bores are coated with nicasil or some other modern surface treatment process. The heat dissipation is much better than cast iron cylinders shrunk into aluminium muffs. Another factor is bore wear is massively reduced by using piston rings much thinner than would have been used in old british bikes, i have a piston here from a ducati superbike and the rings are about 1mm in thickness, compared to maybe 5mm for an old brit.

Andrew.......AMOC list an offset alloy cylinder in their spares list, may be an alternative to a lot of swarf.

This assumes it's not a project towards a diploma????

Good luck with the project

Whilst I am regularly in awe of the work some folk produce on Myford lathes and have never used one they, look a bit wanting for the application you have in mind. As has been mentioned some form of pumped lubricating seems like a necessity.

Hi Andrew In my dark past I had to make some oil coolers and they were of a similar nature and also made of aluminium. We made a blade of gauge plate just clear of the slot size and screwed and inserted to a block to the side that would fit into the toolpost and simply screwed a round carbide tip to the top of the blade. The blade was about 10mm x 30mm gauge plate too tall for the toolpost but fastened to the side block it was stable and sturdy.

David

Phill Irving wrote a book on motorcycle engineering and design and it had a piece on fin design was a double vee arangmemt but they were cast in but you could emulate them by grinding a form tool (or two LH and RH)after plunging straight in with a parting type tool each slot was pitched at 3/8'I think but you can match of the cylinder head.

Sorry I can not give you the title of the book as it is stored in another country (N.Z. I am in Aust) hope thi gives a bit more food for thought, good luck with the project .

Gentlemen, thanks very much for your replies. My bike is a 1954 500cc 93mm stroke model and I am trying to create a 'clubman's' model as per the factory 350 model entered in the TT in the late '40s but in the larger size; alloy barrels for the '56 on 86mm stroke version are readily available but too different to modify; the earlier 93mm alloy barrels are unobtainable and have been so for decades. I did consider a casting using the cast iron barrel as a pattern (shrinkage would not be an issue) but I have been advised that the fin surfaces are not smooth enough and they are almost imossible to get at as the gap between them is about 3/8 inch. I planned to use a press fit liner as per BSA and Vincent as it would be easier and less dimensionally critical for me as an amateur machinist. I have seen a 350 alloy barrel made on a lathe, and KTT Services make them for Velos, so I know it can be done. Alas, Bracknell Tech Colleg has very limited facilities - 1 x Harrison lathe, 1 x Bridgeport mill, no rotary table. They had a full engineering set up until last year but then stopped teaching apprentices and sold off most of the machinery - what chance do we have of ever making stuff again?!! A few years ago I attended Model Engineer evening classes at Newbury College - they also closed their engineering dept but kept the Astrology and Cake Icing classes - is this our new industrial heritage???!!! So, I thought it would basically be lathework but the idea of turning up a pattern has its attractions as it can be built up a fin at a time - any suggestions for material? I can find suitable parting inserts on the web, but nor holders - any ideas? If not, the guage plate idea looks good. Thnks again for your help, Andrew

Andrew, I have a selection of part-off tools to re-home for beer money. (just retired). Contact me if you are interested. Roy M.

Years ago before plasma cutters and laser cutters which would have made life so easy I made a barrel for an early racing Motobecane 250. OHC with face cams.

This was an iron barrel but very close finned, I had no barrel, just pictures but the foundry was shy of trying to do one given the close fins.

I finished up cutting each fin out of sheet steel, probably 4mm and feathering the fins off with an angle grinder and sander.

Starting from the bottom I welded the fin onto a steel tube with a fair amount of weld which was then turned to a root fillet and faced off ready for the next fin to sit on. Second fin was welded into place and so on.

It was a pain feathering the fins off but it meant I could keep the unique outer shape of each fin very easily and there was a lot of variation in size from top to bottom both in size and outer shape.

The lower fins were more circular but the upper fins more square and they had the bevel tube inside the fins and not just a cutout.

When all welded, blasted and painted it looked awesome

I have p.m.ed you.