Re: Meddling with a Wisp

You can drop the floor of the exhause carefully using a file so you can get alignment, or you can drop the cylinder a little with a thinner shim and slightly ramp the periphery of the piston crown at the transfers. Keep in mind that the two base gaskets you now need will have volume and also will compress, good practice is to have 4 tubes on the cylinder studs so you can torque the nuts onto the assembly while you index the cylinder.

If you do decide to ramp the crown, just be wary of the margin over the rings at the exhause. You do not want to take it down too far because the reversion wave from the expansion chamber will be blasting charge back into the cylinder. If it is knife edged then that area or the periphery can erode quickly.

rampexhausetransfers.jpeg

Re: Meddling with a Wisp

Nice one Reb, that's loads to chew on over the weekend. When I started this project I thought 2 strokes would be easier than 4, learning loads tho

Re: Meddling with a Wisp

> Rebel Moby Wrote:

> -------------------------------------------------------

> You can drop the floor of the exhause carefully using a file so you can

> get alignment, or you can drop the cylinder a little with a thinner shim

> and slightly ramp the periphery of the piston crown at the transfers.

> Keep in mind that the two base gaskets you now need will have volume and

> also will compress, good practice is to have 4 tubes on the cylinder

> studs so you can torque the nuts onto the assembly while you index the

> cylinder.

>

> If you do decide to ramp the crown, just be wary of the margin over the

> rings at the exhause. You do not want to take it down too far because

> the reversion wave from the expansion chamber will be blasting charge

> back into the cylinder. If it is knife edged then that area or the

> periphery can erode quickly.

> >

My FA50 has had this mod for about the last 1.5 years . I had no reservations about doing it , as I had done the same to my TM125 back in the early '80s . That produced excellent results as has this latest mod to the FA50 .

Re: Meddling with a Wisp

Cheers PD, that's good to know, don't suppose you have any pics of what you did? Or a link to a write up?

Whilst I hatch a plan for the exhaust port I thought I'd crack on with Reb's head mods for unshrouding the spark plug.

Firstly, I tried marking out the way Reb did but, because I'd already polished it, I couldn't see what I was doing so I sharpied the whole thing.

20200923_123624.jpg

Next I removed sharp edge all the way round turning it into a flat land using a dremel, generating a flat at this point makes measuring what's being removed easy. I worked behind the plug aswell to blend into the larger bore.

20200923_130149.jpg

Starting to blend that flat into a radius, using the dremel, turning that single flat surface into three, again makes seeing what's being removed easy.

20200923_131024.jpg

Re: Meddling with a Wisp

Working with papers all the way through to 1500 grit.

20200923_133029.jpg

The finished item, nice and shiny.. again.

20200923_164937.jpg

I just assembled the engine as it stands at the mo (without base paper gaskets) just to get an idea of what's going on at the top. The squish is shot, 2mm, thanks base spacer! But CR (measured with thick oil) is surprisingly respectable 9.28:1, I thought it would end up considerably lower. Not happy about the squish but might have to live with it. Any thoughts or suggestions???

Re: Meddling with a Wisp

> Tom Boyd Wrote:

> -------------------------------------------------------

> Cheers PD, that's good to know, don't suppose you have any pics of what

> you did? Or a link to a write up?

>

There really isn't much to the whole deal .

The illustration Rebel posted is almost exactly what I did , with the exception of the transfers . I took the transfer troughs down equal to the exhaust trough , which was very close to half way between the top edge of the crown and the top edge of the upper landing . And , my troughs are a bit more straight from the crown edge to it's center , as opposed to the seemingly angled rearward transfer troughs in the illustration .

Re: Meddling with a Wisp

From what I have learned the only thing you can do about the squish is to deck the top of the cylinder down to reach the desired squish. It is going to end up a little larger once you add in the gaskets too.

Your work has been great so far. How you kept that dremel from running all over the place while working on the head is beyond me.

Re: Meddling with a Wisp

Cheers Jay! I've been thinking about your idea of decking the cylinder. I don't fancy trying to fly cut it incase I chip the lining, I'm might try to find a local firm to grind it but I have a sneaky suspicion it'll cost a kidney.

As for the dremel I made a little guide, (carbide shank sized hole in a bit of brass or similar, trick I learnt from a retired tool maker), hold the guide in one hand and dremel in the other, totally useless in a pocket tho.

Re: Meddling with a Wisp

So lay the brass on your part and just dremel into the hole on the brass. Makes sense to me! That way if it jumps it jumps to the top of the brass and not all over your part. Thanks for the tip.

Re: Meddling with a Wisp

I know you guys will be as surprised as I was, no one makes a performance inlet manifold for a wisp!

Turned up some bushes so I could hang the engine in the frame and take an angle off the inlet face. With the cradle at its mid adjustment point the inlet bubbled out near as damn it at 55deg.

20200923_122144.jpg

I had a bit of 1"x4" lying about so set it up and touched on to set x and y datum.

20200914_142638.jpg

Set up an 1" ripper to machine to width

20200914_143927.jpg

Re: Meddling with a Wisp

Set up vertically and drilled a 12mm hole (forgot to pic) then set up at 55deg.

20200914_160637.jpg

Machined the inlet mounting face, that 12mm hole has elongated to 14mm, inlet port height is 14.5mm

20200914_162820.jpg

Measured off the top of the inlet hole to set another datum so I could cut the 6mm stud holes.

20200916_111036.jpg

Re: Meddling with a Wisp

Cut off the bit I wanted from the block, set up and clock in, machine to finished length and open out to 16mm but not all the way through.

20200916_132025.jpg

Set up the face machined at 55deg on parallels and start cutting down for the carb mount. I left a chunk for the inlet flange for loads of blending room.

20200916_150731.jpg

Boring the od to 19mm

20200917_163815.jpg

Re: Meddling with a Wisp

The finished item

20200923_120240.jpg
20200923_120440.jpg
20200929_143554.jpg

What were you saying Jay about slipping with the dremel! Right at the end 'oh there's a little bump' jumps out twice, ffs.

Re: Meddling with a Wisp

20201007_150453.jpg

Oh hells yeah!! 16.16 sha and new pipe donated to cause as well.

Re: Meddling with a Wisp

Jeremy Homser /

Looks great! Fantastic work Tom

Re: Meddling with a Wisp

Almost looks like that'll work . ;)

I really miss having a shop to play in . ;(

Re: Meddling with a Wisp

Dude that is crazy good work on that intake!

Re: Meddling with a Wisp

Haha wow, indeed! That intake is something else, I probably would have brazed a tube to a flange in about 20 minutes but that's a work of art

Re: Meddling with a Wisp

Cheers guys, probably should have just brazed a pipe up but fuck it, it only took far, far too long to make😊

Re: Meddling with a Wisp

SO excellent. That intake is great (scratched it for good luck I see, similar to how they put a goodly scratch into the underneath of the petrol tank on a fresh build race bike)

That Wisp is going to be SO cool.

Re: Meddling with a Wisp

> Rebel Moby Wrote:

> -------------------------------------------------------

> SO excellent. That intake is great (scratched it for good luck I see,

> similar to how they put a goodly scratch into the underneath of the

> petrol tank on a fresh build race bike)

>

> That Wisp is going to be SO cool.

Cheers Reb, yeah that was it, scratched it on purpose for good luck. Wisp racing now.....

Re: Meddling with a Wisp

Check it!!! Just got this pic sent to me.....seats done!

Resized_20201017_144856.jpg

Fuck yarr, wasn't expecting anything like that but love it when a plan comes together!

Ps that tan skull and crossbones is my mate signature.

Re: Meddling with a Wisp

Calling all moby nuts...

The felt seal that prevents grease migrating from the cluth needle rollers into the clutch shoe area, is there a better way (lip seal)???? Clearly previous one didn't work for shit given how much grease is covering everything. Later variator types might have an improved system but I'm stuck with single speed. (edited)

Re: Meddling with a Wisp

Not much room for a lip seal on the clutch. The variator assembly has the advantage of being so deep, so they have a oring on the cover to tend to lube control in the clutch area. The dimoby has just the felt seal.

Picture of the early model, skinny clutch arms with adjustable spring perches and the late model with the larger but lighter arms (there is one model inbetween: large arms and adjustable spring perches)

earlylatedimoby.jpg
50dimobyparts.jpg

Re: Meddling with a Wisp

Tom - that seat is phoquing brilliant !!!

> Tom Boyd Wrote:

> -------------------------------------------------------

> Check it!!! Just got this pic sent to me.....seats done!

>

> Fuck yarr, wasn't expecting anything like that but love it when a plan

> comes together!

>

> Ps that tan skull and crossbones is my mate signature.

Re: Meddling with a Wisp

What a cool project; thank you for posting all these details. Great work!

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