Griffon 380cc engine rebuild - primary drive

[Martin H]

Hi All,

The dismantling of my Griffon 380cc engine continues, albeit slowly.

The nut that holds the front primary sprocket on looks a bit manky see photo

Is the 'screwdriver" centre section part of the nut or the end of the crank ?

Is the thread RH or LH ?

Is it ok to put a bar through the small end and undo the sprocket nut ?

Thank you
Martin

[Stan Nicholson]

Although not a Griffon owner I cannot see that the sprocket/nut would be any different to the Challenger/Silverstone arrangement. If I am wrong I am sure someone will be along to correct me .

Although I have used a bar through the small end eye on engines with shell bearing rods, I am always reluctant to use this method on roller bearing cranks. There is a Greeves special tool (GST 11) that fits between the sprockets to lock the assembly and allow both the sprocket and clutch nuts to be undone and retorqued without putting any load on the crank. There is also a puller (GST 12) if you are going to remove the sprocket, which has to come off as an assembly with the clutch/primary chain.

As for the nut, it certainly looks like the extension with the "screwdriver" slot is part of the nut, not the crank, which is a normal hex but has a slight recess on the back to allow clearance for the end of the crank diameter that carries the sprocket. The crank end has a regular RH thread.

I assume the Griffon should also have the sheet metal lock washer under the nut? This comes as a rectangular, flat part that locates on the crank sprocket diameter and you have to turn back one corner to locate in one of the puller screw holes and turn over one of the other corners to lock on one of the flats on the hex nut. I usually use a little Locktite on the nut as well! As the sprocket fits on a plain diameter with just the woodruff key to stop it rotating, the retaining nut should be tight or the sprocket will fret on the shaft and wear the key.

Hope this helps.

Stan

[Martin H]

Hi Stan

Thank you for your informative post, but .... Oh no.... I looked at my computer too late to read your post. Hope I have not done too much damage

I had decided to stop in the garage yesterday afternoon so took a nice cup of tea out there to peruse what to do next. I noticed two big wood off cuts
that might do to support a bar through the small end, and an old Norton rear wheel spindle was easily to hand and fitted nicely through the small end,
as was a socket and a long socket bar. All set in less than 5 minutes. I decided to just give it a little try to see how tight the nut was, then a little more
and despite the rust and possibly a bit of Loctite the nut was relatively easily removed.

Having now read your post there was not a square lock plate, and I remembered I might have bought the special tool GST11 several years ago....I did,
but it is not for a Griffon - see in photo on wood block. I will get GST11 and GST12 from Gary

The slot is in the end of the crank, not part of the nut. Is this normal ? What is it for ?

The nut, socket, bar and crank end are all in the photo attached. The oil from the primary is rather dark and that from the gearbox not too bad.

The video - if it is attached and can be viewed ? - shows the clutch basket to be a bit wobbly and the primary chain a bit loose. There are scrape marks
inside the primary chain-case on the floor beneath the bike.

Thank you
Martin

PS - Cannot upload video

[AndyB]

I don't think videos can be posted here, but if you can post it somewhere else online (YouTube?) you can post a link to it.

[Stan Nicholson]

Hi Martin, Looks like the end of the crank has been butchered but it shouldn't affect its continued use. The plain diameter outboard of the sprocket thread with a slot machined across the end is used to drive a mechanical tachometer on the race bikes. I didn't realise that the Griffon used the same crank as the Challengers and Silverstones.
The chain does looks slack, and because the top run is usually tight when the motor is running any slack is in the bottom run and the chain rubs the inside of the case. As you probably know, adjusting the primary chain with shims between the crankcase and the gearbox is a PITA so tends to get neglected!
I use ATF (type F) in the primary case and that always comes out black with both the original Albion clutch with friction plates and the all-metal Griffon clutch now fitted to my Silverstone.
Do you intend to pull the clutch and replace the primary chain? This comes off in one piece so no need to disturb the plates. The clutch assembly does float a little but this is normal in my experience (unless a Griffon owner can correct me).
Stan

[Martin H]

Hi Stan

Thank you for the post.

Looks like a large screwdriver has been used perhaps to try to hold the crank to undo the nut ?
As you say, a bit butchered but still useable
Interesting to know the slot is for a rev counter drive.

The chain is very loose in my view. I didn't know how it was tensioned. Now I do. Thanks

I have used ATF - F type in my Nortons for decades so will use it in this Griffon. Thanks

As you can see the clutch has some interesting dents, don't know how they occurred.

I think the clutch outer wobble is not good as there are marks associated with the edge of the clutch drum marking the inside of the primary chain case.
Interesting to know it come off complete..... shall I have a go at cutting the wet lawn or take the clutch off ?

As I said in a previous thread I have never looked inside a Greeves or a two stroke.... perhaps I should have stayed in blissful ignorance .

I was led to believe this Griffon had had little use .....

My intention is to take the engine completely apart and rebuild or more likely get it rebuilt it to as new or close condition.
Or at least super reliable for the road.

Thanks
Martin

[iansoady]

On the Francis Barnett Cruiser I rebuilt a few years ago I made a primary chain tensioner out of a Royal Enfield tensioner blade. It may not work for the Griffon but maybe worth a thought. That way of tenioning the chain using multiple gearbox gaskets seemed a most awkward way of introducing oil leaks, but your engine may of course be totally different.

[Martin H]

Hi Ian

Thank you for the photo and suggestion. Clever stuff. Looking at my Griffon I don't think there is enough room for a tensioner . See photo attached

The home management decided that my time this afternoon would be better spent digging the weeds from between the paving slabs of our patio

However a quick trip into the garage found with the lower chain run tight there is nearly 3/4" total up/down movement in the upper chain run

All packed up ready for Kidlington tomorrow

See you and Stan there?

Thanks
Martin

[Stan Nicholson]

Not me I'm afraid. I live in Canada

If you are going to do a rebuild on the motor I strongly suggest you replace the primary chain. As for chain adjustment when you put the the motor back in the frame, with the separate gearbox (unlike the Villiers engines), it is a lot easier to shim between the motor and the gearbox if the motor is on the bench and the primary drive in place. I did a post earlier about slotting the shims so you don't have to keep removing the clutch/engine sprocket/primary chain assembly, just lever the gearbox back and slip in another shim until the tension is right.

Stan

[Martin H]

Canada.... what sort of excuse is that?

[Martin H]

Hi Stan, Thanks for the advice. I will get a new chain and the slotted shims when on the bench seems a very good idea.


The management required me to do stuff in the garden while the sun shone ..... but the rain returns next week so back in the garage

The end of the crankshaft is a bit butchered and does not fit inside the rebate of the puller. I presume it should fit inside ?

I propose to use a fine file and emery to reduce the butchery such that the end fits inside the sprocket puller.

Any issues/problems I need to consider ?

Thanks
Martin

[Stan Nicholson]

Hi Martin, Only, as I mentioned before, the clutch has to be withdrawn from the mainshaft at the same time the engine sprocket is pulled off. Otherwise, no problem now you have the puller (and the locking tool?) I did make up a puller for the clutch but have found it is not a tight fit and comes off easily without using the puller, on my motor anyway, although the mainshaft is now part of my Nova 6-speed cluster .

Stan

[Martin H]

Hi Stan
Thank you for the reminder to pull sprocket and clutch off together. As you can see from the photo they are both now off.

There is a slight bit of (previous) damage to the end of the crankshaft which made pulling the sprocket off harder than it would
normally have been. I will tidy it up with application of fine emery cloth. As you said the clutch was tight but relatively simply
to pull off as a complete unit. Main shaft splines look good.

Applying hand pressure to try to "wiggle" both the crankshaft end and the gearbox main shaft found no perceptible movement.
So hopefully main and gearbox bearings are both good (?).

The primary chain looks good at initial inspection. Perhaps strange (?), but likely I'll replace it anyway.

Off with the inner chain case next ...