Mark 3 Seeley frame

Hi guys

My first post. I have a Mark 3 Seeley frame made by Dennis Curtis with Commando / Quaife. See https://cmrracingproducts.blogspot.com/2018/10/even-more-cmr-racing-products-down-under.html. I also have an XR69 made by Dennis which has been raced here in NZ very successfully over the past 5 years by Jay Lawrence. And a nice Dunstall Norton to sort out one day.
I am in the process of rebuilding the Seeley after a highside a few years ago when the teeth on 3rd gear let go. I have Ducati SS triple trees with Brembo twin brakes off a Guzzi. My problem is the drive chain rubs on the bottom frame loop. I have read on this site that the standard Norton engine plates have the gearbox mount holes an inch lower than for the Seeley. I still have the Norton chaincase so it will be discarded in order to raise the gearbox. The next problem I expect is that with the standard shock length at 13.9 inches, the swing arm angle will be way too steep. It is already 15 degrees.

Does anyone have specs / plans for the engine plates or any other suggestions as to what is required to get the chain running without fouling. I am currently 19/43 sprockets but could go to 20/45 for some more clearance.

It is important to get the gearbox sprocket at the correct height. I think the centre of mine is slightly above the line from the crank centre to the rear wheel centre. I just set the gearbox and motor up where they should be in relation to the frame, and used cardboard and scissors. Then cut the plates by hand with a jig-saw and linisher belt. It is important to get the motor as far forward as possible. If the bike is light in the front, you will not ride it fast. The chain case is not important, if you use belt primary drive. I use a Manx clutch with single row chain and a floating engine sprocket.
Making engine plates is easy and rewarding. I really like doing it.
I once built a Tribsa with full circle engine plates. It was a very tight fit. I am sorry I sold it.

I'd raise a question about your fork yokes. Too much offset adversely affects the handling. I use TZ350 Yamaha yokes which have 53mm of offset - the handling is brilliant. The bike oversteers both when baking into corners and when accelerating out, it is really usable.

Hi Joseph
I will have a look & see if I did drawings of my Mk3 engine plates. I have raced this but it is my road bike. It's coming down for a full rebuild. I do use Commando primary chaincases with belt drive but open it up to suit the gearbox position ie slotted engine mounting holes in the inner case & no seal on the gearbox mainshaft.
Please ask Seeley 920 for advice, he knows more about Seeley Commandos than anyone!
Sorry John lol.
I know he used the gearbox mountings to change the chain line & help pull the rear wheel down onto the track. Love all these bits of info. I've run Ducati Pantha forks & played with different yokes & as long as you are in the ballpark it's fine. The original Seeley front end set up is perfect. My road belt set up is not the same as my race set up & I use a standard Commando rear sprocket, so Isnt relevant.

Chris said:

Hi Joseph
I will have a look & see if I did drawings of my Mk3 engine plates. I have raced this but it is my road bike. It's coming down for a full rebuild. I do use Commando primary chaincases with belt drive but open it up to suit the gearbox position ie slotted engine mounting holes in the inner case & no seal on the gearbox mainshaft.
Please ask Seeley 920 for advice, he knows more about Seeley Commandos than anyone!
View attachment 116258View attachment 116259View attachment 116260View attachment 116260Sorry John lol.
I know he used the gearbox mountings to change the chain line & help pull the rear wheel down onto the track. Love all these bits of info. I've run Ducati Pantha forks & played with different yokes & as long as you are in the ballpark it's fine. The original Seeley front end set up is perfect. My road belt set up is not the same as my race set up & I use a standard Commando rear sprocket, so Isnt relevant.

Click to expand...

My Mk3 Seeley was in the ballpark with fork yokes from a 450 Ducati. It felt and handled better than my Triton. Then one day as I came off a sweeping left-hand bend at high speed and straightened-up while braking, the bike stood-up and threw me onto it's left-hand side. While I was over the side, I gassed it to get it onto the grass on the left and crash it - it came out of it's silliness. I rode it again after that, and I could feel it trying to stand-up while I was braking. My fork yokes now have 53mm of offset - NOT 65mm, and I can accelerate full blast right around any corner and up the next straight. It makes my bike very difficult to beat. I just sit there operating the controls and let the bike do its thing. More trail made my bike oversteer, and that is excellent.

Have a look at the fork yokes :

Templates mentioned , or wasit drawings . https://www.accessnorton.com/NortonCommando/seeley-mk3-engine-plates-2021.33106/

And while we're at it . The CSR things etc P II cetra , have differant primarys / chain length , just to confuse the issue .

Nice historical photograph Al

Chris said:

Nice historical photograph Al

Click to expand...

About year 2003. It still has the Ducati fork yokes, so the bike looks like a chopper. I did not suspect what it might do when ridden fast. When my mate had it, it was fitted with a Laverda 750 motor which was heavier. So it might have been less likely to stand up and turn. He raced it at Sandown, which was not a tight course. Even though the motor was heavier, but he said he did not like riding it at high speed around sweeping bends at high speed. However he had always raced two-strokes. So he might not have had the feel for it. Two-strokes are much easier to ride fast, but the Seeley 850 can beat them easily, when you know the technique. It is very different.

If the Seeley is set-up right, it can be flicked into corners and accelerate full chat all the way around them steering on the throttle. A Manx Norton will over-steer if gassed when on a lean, and feel really good. With the Seeley, the effect is much more pronounced. I really recommend it. It took me a while to find out how to use it. The effect is not immediately obvious. I found it by continually advancing the transition point in corners. I suspect I could brake before a corner and accelerate from there.
You need close ratio gears and smooth power.