The “low point” is directly under the crank

My earlier thoughts on the newly revamped Cub have sadly come true with a series of….er.. very abrupt
stops and resultant 5’s. In every case these stops are on obstacles that the Cub has sailed over in the
past and never ever been a problem. The bike itself is riding as well or better than before, zero
handling problems and with the crankcase breather and expansion box fitted no stalling 5’s this year
in any sections.

The Cub front frame is not  quite horizontal on the underside tube which dips down nearly an inch at
the front. Wrap an alloy bashplate around this portion of the frame and the lowest point of contact is
now the front! With the SM poly carb unit it is narrower and slippy at this point whereas mine is more
like a full width snow plow.

Low point just aft of the bolt hole

Looking at other designs the leading edge and radius needs to be shallower such that underside
obstacles will flow undernneath while the bike’s inertia will carry it forward.

The shallower angles of the Armac design

A lot of discussion with Guru, Ray, on the subject and what we now have in mind is a shallower curve,
NO LOWER TUBE, an angle change where the plate fits on the rear downtube and a revised front
engine mount. Now of course I could saw the tube out myself, beat the crap out of the plate but as in
most things this might work but would most likely look awful as I don’t have the equipment to
professionally adjust the angles……. so once more portions of Cub will be sent to CA for some more
of Ray’s Magic.

Currently there were no plans to ride Roswell but Brenda mentioned I could take the car, so just
maybe 2 more trials this year ? Of course if I do ride then there will be a lot of lofting over anything that
could conceiveably be a problem

Ray also says that we can reposition that front engine mount higher on the frame which will lift the
motor and reduce the leading edge angles. He also mentioned coating the underside with some poly
stuff to give it a slippery finish…… all sounds good to me.

The most popular, and expensive front frame is from Armac in the UK, and in this total redesign of the
frame. There is no lower tube and a shallowish but near horizontal plate which can be seen in all these
pics taken at the recent Manx Trial.

A pride of Cubs at the Manx

One step plate

Standard shallow curve on the Armac

Same here

As can be seen from all these plates they are generally MUCH flatter without the curve, which although
looking pleasing and beautiful is proving to literally be a show stopper. With the old SM poly carb it was closer to the tubing, narrower at point of contact, and perhaps flexed a bit on impact. The following pic
shows how the front lump is lower as when the bike in on a workshop stand, with the bashplate
horizontal the front wheel is in the air and the rear almost in contact with the floor.

The original SM plate

Closer, tighter and narrower in the problem zone

With the bike on a stand easy to see how much lower the front is

As far as I can see (not being a fabricator) this is what needs to be done to correct the problems. Now
Ray can do this using a dummy engine and then when he has the design sorted I can cut off the lower
engine mount at this end if required.

What we have and some of MY ideas

First remove the offending lower tube. Ray says the lower plate mounts will need the angle adjusted
to come closer to the horizontal. Raise the front engine mount and fit a forward bashplate mounting
bracket. With all that done and a dummy engine in place the gorgeous alloy can be reworked with
shallower angles. We will see what the Guru comes up with.


What did you think of this article?

  • No trackbacks exist for this post.

  • 9/19/2012 11:56 AM Bil Todd wrote:
    Tony why not put the plastic SM bash plate back on?.

    Reply to this

  • 9/25/2012 9:23 PM Dan Straka wrote:
    I like that last picture of the design drawing. I think that’ll bring things on par with Armac. That raised engine mount up front would probably even fix the issue where the head pipe is so close to the engine like on mine.
    Reply to this
  • 10/10/2012 10:17 PM trev wrote:
    Hey Tony, pleased to see the cub is working well apart from the bashplate. I’m sure the remedy you’re proposing will give heaps more clearance and ‘skidabillity’. As the engine/carb set up is as the old bike….was wondering what difference the ‘Bulge’ next to the barrel has made to the performance? I hear it’s supposed to enhance the tractability….is this so ? cheers Trev
    Reply to this
Leave a comment

Submitted comments are subject to moderation before being displayed.


 Email (will not be published)


Your comment is 0 characters limited to 3000 characters.



Leave a Reply

Your email address will not be published. Required fields are marked *