Greeves Griffon Gearbox Help Needed

[Kim275]

Hi,
I have two Greeves Griffons - which are currently being re-built to get ready for next years season - both of which need some attention to the gearbox. Does anybody have any diagrams available for the Gearbox?

My 250 Griffon - clutch shaft is badly out of line - (the primary drive chain - even though new is very slack) and the shaft is very close to the front edge of the adjustment hole in the clutch case - which I think means that the gearbox has been shimmed incorrectly?.

Thanks for any assistance anybody can give here.
Cheers Kim

[mudmonkey]

griffon gear box

hi there

depending where you are in the country/world....

Geoff nunn does many greeves gearbox's for the pre 65 scrambles club riders

he used to work at the factory in the day

very helpful & knowledgeable guy

[John Wakefield]

Where in the world

'depending where you are in the country/world....'
Good point there Mudmonkey it would be helpfull if all users stated their home country in their profile. In fact it should be mandatory, as I have wasted time giving info on UK suppliers etc only to find the person wanting the info in on the far side of the world.

[Bearingman]

Hi,
I have two Greeves Griffons - which are currently being re-built to get ready for next years season - both of which need some attention to the gearbox. Does anybody have any diagrams available for the Gearbox?

My 250 Griffon - clutch shaft is badly out of line - (the primary drive chain - even though new is very slack) and the shaft is very close to the front edge of the adjustment hole in the clutch case - which I think means that the gearbox has been shimmed incorrectly?.

Thanks for any assistance anybody can give here.
Cheers Kim

Hi Kim,

The Griffon gearbox is pretty much straight forward. If your new primary chain is way too loose, make sure you received the correct chain for your 250, as the 250 has a smaller engine sprocket than the 380. The factory used a small number of shims to keep the chain in alignment. It sounds like your supplier gave you a 380 primary chain by accident. Compare your old and new by hanging them together from a small diameter rod or just count the pitches of the chain.

Also...If you have your g/b's apart, keep a eye out for the needle bearing that supports the lay shaft, as when this bearing fails, all hell breaks loose! At Nicholson Motors, Nick would replace the needle bearing with a bronze bushing, which I have done on mine as well.

I have a more than a couple gear box shells which have been repaired in the area of the lay shaft bearing housing.

Good luck!

Kenny Sykes
USA

[Kim275]

Greeves Griffon Gearbox Help

Thanks Kenny - I have some old 380 chains so will double check I have the shorter chain for the 250.
Cheers Kim

[Rob]

Kim,

Which type of Griffon gearbox(es) do you have? I am just working on a 'Jack Knight' box. We gave the bike a try at the last Mark's Tey event and had a few troubles with gear selection. Then, two of the holding bolts went AWOL and all the oil poured out! Oh, how we laughed (**!?*!!**??)

Best one I ever saw was at our local practice ground years ago. A lad with a 380 had the throttle stick open. As the thing roared away, the gearbox end cover screws undid themselves and the all the oil ran out of the end! Oh, how we laughed that time too!

Many years later I bumped into him in a local pub. He still had the bike and agreed to sell it to me for the price of the gearbox repair, £80 - it couldn't be any cheaper because it was 'a proper works bike'. It was too, frame number GPWM2! Oh, how I laughed really happily that time!

[druid]

Rob,

It is known that the Jack Knight boxes can have a problem selecting 2nd/3rd gears. The dogs were made wider by Jack Knight which decreased the engagement clearance, this seems to cause the problem. Big tooth PGT and Albion clusters don't have the same problem.

Druid

[Kim275]

Greeves Griffon gearbox Help

Hi Rob/Druid

Thanks for your input - nice to know I am not the only one with griff gearbox challenges !!
Not sure what type I have - how do you tell?

I have a 250 griffon (1971) and 380 QUB Griffon. (1972)

The 250 bike is new (to me) last season and only rode it a few times - but occasionally it slipped out of 3rd gear (could have been rider error of course!).
The problem I have withthe 250 is the primary drive chain is slack (new chain) - checked it and it is a 250 chain. but also the clutch shaft is too far forward - as the adjuster is close to front edge of theadjustment acceess hole. I am hoping that I can resolve with alignment/shimming.

The 380 gearbox is the best I have had (or at least was ) - rebuilt by Geoff Nunn last year - and was sweet - until my crank nut came off (as i headed over a jump) - jammed between the primary chain and the clutch teeth. As I came to an abrupt stop (understatement) - I looked down and all oil had deposited on track - chain case split. (moral of that story is after a £1200 complete engine/gearbox rebuild + new clutch - check nuts for tightness first before riding !!).

My Dad has the gearbox out at the moment and is checking the clutch shaft for 'bends' - but I suspect the worse and think we will need to re-build. Also the casing cracked around the top left crank/gearbox bolt - so this is being welded up.
Happy Days !!

[mudmonkey]

primary chain

hi kim

i ride a 250 griffon aswell

i can check the number of links in the primary chain if you would like ?
i took me 3 attempts to get a chain with the correct number of links from my supplier....

regards


david
265

[Kim275]

Hi David - that would be really helpful - I will check mine this morning and then we can compare!

By the way what rear sprocket do you use on the 250? - I have a 54 tooth sprocket - but think the bike is too high geared in first - --- really slow off the line before she gets into the power band ----- (whereas my 380QUB pulls a 52 tooth - and I think 54 is standard 380) - suspect the 250 needs more like a 56+? - not sure what the standard sprocket size was for a 250.

cheers Kim

[John-Boy]

According to the Griffon Parts manual (1969-71), the 250 should have a 21T engine sprocket with a 68P primary chain. The gearbox final drive sprocket should have 13T and the rear wheel sprocket 54T (on the 250 and 380).

The main difference between the 250 and 380 is that the latter has a 25T engine sprocket with a 70P primary chain. The clutch sprocket is common to both models.

With this setup, first gear on the 250 should be 21 to 1 whereas the 380 is higher at 17.7 to 1.

I hope this is of some help.

[Kim275]

Hi John,

Great help - measured the 250 - and indeed it does have a 21T engine sprocket and 68p primary chain (checked my 380 and that has 70p)..........Also - my final drive sprocket is 13T - so gearing ios standard - then the problem is with the engine power.......re the slackness of the primary chain - then the gearbox must need shimming back to tension the chain.........is there a measurement to determine the correct chain tension?

cheers Kim

[John-Boy]

Kim

Most of the advice I have seen from Greeves is on the lines of "Ensure that any shims are refitted exactly as found" - which is not very helpful if you don't know how many were in there originally.

The Griffon parts manual refers to two different types of shim but does not give their thicknesses or number, just "as required"

I guess it is going to be a trial and error exercise unless an expert like Geoff Nunn is able to advise.

By the way, I bought the parts manual on CD pretty cheaply from a guy on e-Bay.

John

[Kim275]

Thanks John,
I will try and have a chat with Geoff - and see what he recommends