Odd flywheels

Helpful information and requests for assitance and advice
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dch
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Joined: Thu May 24, 2018 12:56 pm
Location: New South Wales AUSTRALIA

Odd flywheels

Post by dch »

Hi all,

Just pulled down a 51/ 18s motor which has g9 stamped on flywheel on drive side and a g3 on the cam side. Are these no's correct?Was thinking they may be from 2 different motors.

Cheers David
SPRIDDLER
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Re: Odd flywheels

Post by SPRIDDLER »

Welcome to the Forums, David.

This previous Forum thread may clarify:

http://www.jampot.com/forum/viewtopic.p ... rs#p153012
'There is a tide in the affairs of men
Which taken at the flood............'
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Rob Harknett
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Re: Odd flywheels

Post by Rob Harknett »

Further to my comment you would have seen, if you viewed the link Neville gave. If you see a number cast on a part and consider it to be a casting number. You could do a bit of detective work. Check the number against the old/new parts list converter. Here. http://archives.jampot.dk/book/Spares_l ... ements.pdf
If the part was used post 1951, you may see the number has a new part number. Up to about 1,000 parts would have had a number like this 38-22-E followed by a number 1 up to about 1000. The new pt. no. will be that last number after the E prefixed by as many Zero's as it needs to make a 6 digit number. The example I have given 38-22-E?? will be found cast inside the AJS outer timing cover, used up until when I was changed when the SR1 mag was fitted. ( up to 53 on 500's up to 54 on 350's ) 38 means the year the part was introduced, 22 the smallest 0r cheapest model it fitted. Model 22 being the 1938 250 OHV mag. ign. single. What does the letter E mean? It means it was an Engine part. F would mean frame, FF front forks etc etc.
Also check this part number converter book if looking for a post 1951 new part number, You can then discover if club spares have the part by using the new pt. no. to check with. Some parts used into the 1960's were introduced as long ago as the 1920's.
I am repeating myself here, but eventually more people will discover how to help them selves find parts and know a little more of the history how the bikes evolved, yet still retained parts first introduced many years in the past.
dch
Posts: 3
Joined: Thu May 24, 2018 12:56 pm
Location: New South Wales AUSTRALIA

Re: Odd flywheels

Post by dch »

Thank you Spriddler & Rob for your information , it seems to be a bodgie crank.



What I need to know now is can i recondition the crankshaft with a g3 flywheel (350) one side and a g9 flywheel (500) the other side.Are they interchangeable? Part no's are different.

Regards David
SPRIDDLER
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Re: Odd flywheels

Post by SPRIDDLER »

dch wrote:What I need to know now is can i recondition the crankshaft with a g3 flywheel (350) one side and a g9 flywheel (500) the other side.Are they interchangeable? Part no's are different.
Has the bike been run with those flywheels or is it an unknown and new to you?
After 1948 the 350's used the 500 crankcases and flywheels so they were common between both engines even though the 500 f/wheels were previously marked G9 and the 350's flywheels were marked G3. The 350 f/wheel assembly was balanced differently from the 500 to allow for the difference in piston weights.
I think you'll see that the way the drive side axle locates in the flywheel is different from the timing side hence they are not interchangeable and will therefore need different part numbers anyway.
If you obtained the engine as a box of bits you need to be aware that there were some changes to the timing side axle and oil pump plungers ('one start' and 'two start' designs) so you need to be sure that the plunger splines match the scroll on the timing side axle.
If it has been running o.k. and the big end is serviceable and the drive and timing side axles are o.k. I wouldn't do any more with regard to splitting/refurbing the f/wheel assembly.

BTW - You can find all the manuals for your bike under 'Books' here:
http://archives.jampot.dk/
'There is a tide in the affairs of men
Which taken at the flood............'
dch
Posts: 3
Joined: Thu May 24, 2018 12:56 pm
Location: New South Wales AUSTRALIA

Re: Odd flywheels

Post by dch »

I've never had motor running .I bought all this stuff 40 years ago and it has been sitting in a shed all this time.These old bikes finished there days as “ paddock bashes “ so they are pretty rough.Cam side main bush flogged out also loose in crankcase.Will need to find another case or make an oversized main bush.As for the flywheels will split them ,then make a decision.

Thanks again for your time and effort in supplying me with your knowledge, it's been a great help.

Cheers David
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Re: Odd flywheels

Post by SPRIDDLER »

You're welcome.
You probably realise the following anyway but if not (and being unaware of your workshop facilities) .........
The crankcase halves were matched at the factory and by line boring the drive side and cam side axle bearing positions to keep the c/shaft assembly true and unstressed so I'd go for an oversize bush.
Obviously the cam side bush shouldn't be loose but it should have a peg to prevent it rotating.
I had an oversize cam side bush made from aluminium bronze by a plastic injection mould-maker pal who reckoned it would be a 'better' material than the usual phosphor bronze. Frankly, the phosphor bronze material is fine but he was keen to use ali-bronze.............and as he was doing it for free :beer:
Just a final point that if the cam side bush is knackered the axle will have hammered so the oil pump drive scroll and the pump plunger splines need careful examination.
Good luck - it's sounds a very rewarding and worthwhile task after 40 years dormant!
'There is a tide in the affairs of men
Which taken at the flood............'
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