Mark 3 Seeley frame

J

josephoneill

Joined
Aug 7, 2011
Messages
1
Country flag
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.
 
Last edited:
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!
Mark 3 Seeley frame
Mark 3 Seeley frame
Mark 3 Seeley frame
Mark 3 Seeley frame
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.

ibb.co

LHS-1 hosted at ImgBB

Image LHS-1 hosted on ImgBB
ibb.co ibb.co

ibb.co

RHS-1 hosted at ImgBB

Image RHS-1 hosted in ImgBB
ibb.co ibb.co
 
Last edited:
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.
 
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...
Greetings!

My name is Rob. I would like to ask a question of Chris, I believe, with the green Mk3 chassis? I too am assembling a Mk3 road bike and I am curious as to how your side stand solution worked out. If you wouldn't mind letting me know and, if successful (!), what type you used, I would really appreciate it. Otherwise, laying the bike over may be my go-to 😁.

Cheers,

Rob
 
Hi Rob
It's from a Kawazaki if I remember right. It's mounted on the front of the engine plate & is just this side of Safe. I really need to weld a small foot pad to it. I will find a photo that is some use lol ie the other side of the bike.
Mark 3 Seeley frame
 
Hi and THANK YOU, Chris!

Indeed, your bike came together nicely. Congrats.

I am just getting started, fitting the engine plates. If I could sort the side stand solution at this time, i.e., instead of after the bike is otherwise done, it would be wildly out of character for me. But here I am ...

I was just looking at a stand from a Triumph Street Triple 675R (c. 2009-2014). Two bolt fixing, and there are aftermarket adjustable legs available online, if needed. Yes, please let me know any tips on yours that you think would be helpful. Very much appreciated! As for me, parking it on a hill, left side up, would be a 100% success 🙌.

Please let me ask, how did you resolve your top engine mount, if you don't mind? I am envisioning fabricating a bracket similar to the std Commando head steady in design, but aligned to the Seeley centerline longitudinally, with the side plate holes positioned such that the engine is "level" in the chassis. Or something like that 😁.

Enjoy your evening!

Rob
 
Hi Rob
If you are going to use Commando inner & outer primary cases? You need to mock up your engine plates & fit the stand after, as standard Seeley Mk3 engine plates dont leave you a lot of material. Building your own plates for the road you can make that bottom section, gearbox to front engine mount deeper. My original photos in this thread are as good as I have. Joseph's idea of the Triumph 675 stand sounds good, it must be a two bolt set up. Being able to adjust the length would be good. I have a tiny rod welded on to just clear the primary case & allow me to put the stand down, although I never got round to cutting the right angle on the bottom of the leg & welding on a footplate
Headsteady, dont tie it in tight. This is a link to a Titchmarsh frame, get some bosses made & welded on then you can use rubber bobbins, a much kinder setup. My frame has the headstock gusset & provides minimal support. I've mentioned before, Dave Watsons race bike used a tiny strip a strap really just to tie it in,. Not the best picture
 
I guess the engine is a stressed member for those of you with only half a frame (ie mk3) ?

If so, this might not be very helpful / applicable…

Minnovation Racing make / use mk2 frames and Martin uses an isolastic type head steady even though the motor is rigid mounted. He reckons its gives the best balance of support and reduced vibration.

It’s quite a robust affair, much bigger and heavier than it could be without the rubber. I haven’t experimented with anything different, choosing instead to bow to his experience in the matter.


Mark 3 Seeley frame
Mark 3 Seeley frame
Mark 3 Seeley frame
 
Fast Eddie said:
I guess the engine is a stressed member for those of you with only half a frame (ie mk3) ?
Click to expand...
The way I see it, the engine is not really a stressed member in this case. The frame doesn't collapse without the engine, does it? The frame triangle should ensure it doesn't.
With a rubber mounted engine, the possible stiffening effect is lost. The engine just hangs there as a mass lump.

- Knut
 
My Mk3 Seeley frame is an original, and intended for a Commando motor. On the inside of the top tubes there are two bosses a bit back from the head. I tapped the two holes in the rocker-box bigger with a coarse Whitworth thread and made two short rods out of tube with large rose joints at each end. The rods take the torque reaction of the motor. Theoretically the top of the motor can vibrate slightly sideways - but not fore and aft.
Bill Horsman was racing Gerry Kooistra's Mk3 Seeley G50 - said he could feel the front walking when he pushed it hard. But I use a bit of gusseted chrome-moly tube in front of the motor - not the ladder.
 
I suggest more people should build Seeley Commandos for racing. I am amazed that the Commando motor is fast enough because of the way the frame handles. When you can power full blast from extremely early in corners - that is a very convincing argument.
 
My mk2 has a solid headsteady, it's a much more robust frame being full loop. My Mk3 doesn't have the bosses just a couple of tabs to mount a headsteady to so not as robust. It also has 2 clamp on front tubes & I think this allows a bit of movement on the front end. Commandos shake a fair bit & I'm the opposite to Al, I don't want to much side to side. Really not sure about solid mounting the head on a Mk3.
 
I am certainly no Ken Sprayson, Colin Seeley, etc so take this with the pinch of salt it may deserve…

But… I don’t see the mk3 as being well triangulated. There is a point at which the headstock triangulation and main frame triangulation meet (red arrow in pic below) and at that point there is no triangulation.

To my eye, the frame needs the motor to add an additional triangulation. So, sturdy engine plates and a rigid head steady look like they’re needed (by design) on the mk3 to me ?

IMG_3890.jpeg
 
Last edited:

Similar threads

Bigbossmonty
  • Locked
Norton 750 engine plates-Seeley frame
Replies
3
Views
1,242
Chris
Chris
Back
Top