Engine Identification

H

Hagarr

Joined
Jun 5, 2022
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Hello All
I have an Engine i'm attempting to identify if others could please help.
It is running a Joe Hunt Magneto, Drive end of crank has internal thread, not external as most I have witnessed.
Engine number is 315678.
Bore is 80mm +0.50mm appears to have liners fitted, unknown crank configuration.

Thank You
 
Hagarr said:
Hello All
I have an Engine i'm attempting to identify if others could please help.
It is running a Joe Hunt Magneto, Drive end of crank has internal thread, not external as most I have witnessed.
Engine number is 315678.
Bore is 80mm +0.50mm appears to have liners fitted, unknown crank configuration.

Thank You
Click to expand...
Photos please
 
Photos are on my phone and a pain to get onto websites. Not much to show to be honest, as described in previous message.
 
If you Google your number (which you could do) it looks like late '74.
Standard bore for an 850 is 77mm so at 80mm it is more than +0.5mm

Can't say more than that with your limited description. Joe Hunt was never fitted as standard. Crank has been modded by someone.
 
You can add the 'Direct Link' postimages have under share and embed it into your post.

Engine Identification


You have a late 850 MK2/MK2a engine with a large bore kit of one of the 920cc variety if the stoke is unchanged. Question is which of the 920 kits.

RGM have 2 kits in their history, the early one had a slightly smaller bore but weak pistons, current offering has larger bore and stronger pistons.

Details here


For those whose so require we can supply oversize pistons, (our standard size pistons are marked
0.5, oversize 1.0) These are exactly the same as the pistons previously discussed but are
designed to run in a bore of 3.211. The old (and no longer made) 920 piston was adapted from a
ford cross-flow engine, it had the disadvantages of a larger gudgeon pin, excessive weight, and too
much length both above and below the pin. This piston required extensive alteration before it
could be used, and in its non Powermax version had a taste for self destruction. The nominal bore
size for this piston at STD size was 3.188”.
Click to expand...
So is the bore 81.5mm or 81mm, if it is 80mm then you have someone else's kit.

Turn over the engine and see what the stroke of the piston is in case the crank has been stroked.

If you plan to use it as a road bike then the driveside crank end has had the alternator shaft extension removed.
 
Last edited:
Someone has been inventive on the timing side, but swapping the cam driven points assembly for the earlier magneto assembly is not straightforward so I would like to see it complete with cam sprocket and chains fitted.
There is no provision for an alternator so presumably it was intended for racing only. A non standard cam is likely to be fitted and what head does it have?
 
I’ve just realised that the chain tensioner for the magneto is on the loaded chain run. You should move it to the unloaded chain run. There is normally no separate tensioner for the magneto chain because tensioning was done my moving the magneto but presumably that is not possible with the Joe Hunt magneto.
 
kommando said:
You can add the 'Direct Link' postimages have under share and embed it into your post.

Engine Identification


You have a late 850 MK2/MK2a engine with a large bore kit of one of the 920cc variety if the stoke is unchanged. Question is which of the 920 kits.

RGM have 2 kits in their history, the early one had a slightly smaller bore but weak pistons, current offering has larger bore and stronger pistons.

Details here



So is the bore 81.5mm or 81mm, if it is 80mm then you have someone else's kit.

Turn over the engine and see what the stroke of the piston is in case the crank has been stroked.

If you plan to use it as a road bike then the driveside crank end has had the alternator shaft extension removed.
Click to expand...

Thank you for your answer and knowledge.

Ok Clearly I need to delve further

I had considered checking cam lift if nothing else but i'll confirm bore size with mic and stroke.

I'll also need to look further into the boxes of bits for what may be a fix for the alternator end as the bike was definitely street ridden.
 
OK

Confirm, although piston indicates 0.5 o/s, measures 81.07mm.
Liners don't appear stepped as per the RGM kit, maybe stepped at bottom of bore.
Std stroke at 89mm
Next is to attempt cam lift as a minimum

N.B. tensioners are loose, so not in running positions.
 

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