Ask an Engineer

[Grumph]

Take a look at a speedway bike as an example of "big engine minimalist frame" Engine plates on those are 6mm aluminium

Yeah, and the engine sprocket has to float to allow for frame flex......

[pete-blen]

Take a look at a speedway bike as an example of "big engine minimalist frame" Engine plates on those are 6mm aluminium

Yeah, and the engine sprocket has to float to allow for frame flex......

The foating engine sprocket is a carry over from the old clutch system.. the clutch basket use to float when the clutch was pulled..
The new clutches the basket is fixed to the shaft...
Speedway frames do crack... but it takes a while... but then they are only running in anger for around 90 secs at a time..
think we use to cut out a lap of Nelson in 20/21secs on a good surface X 4..
When you come off the slide & the rear hooks up.. You can feel the frame trying to tie it self in knots.. one of the main
reasons they wobble in a straight line...

Had a Briggo Jawa / MK3 Weslake way back when..

[pete376403]

Lemesee - started with Mattingly framed JAP 4 stud, that engine (or bits of it) went into a NZ made replica Jawa frame, then the JAP got replaced by a Jawa 2v, then a Mk1 Weslake (horrible piece of unreliable shit), that got tossed for a Jawa 4V and thats more or less how it went for the 16 odd years that I was riding at te marua, with side trips to Wanganui, palmerston north, meanee and kihikihi. Bit of a 'grandfathers axe" bike. Love to try it again.

Sorry about hijacking the thread. As you were.

[Brian d marge]

Yeah, and the engine sprocket has to float to allow for frame flex......

Just been watching the Dakar , got a shot of the mini , very nice roll cage ,,,( not sure yet ) but looked monoque and very stiff

beautiful

Stephen
sod me , did I spell monoque correctly , damn ......

[Brian d marge]

The foating engine sprocket is a carry over from the old clutch system.. the clutch basket use to float when the clutch was pulled..
The new clutches the basket is fixed to the shaft...
Speedway frames do crack... but it takes a while... but then they are only running in anger for around 90 secs at a time..
think we use to cut out a lap of Nelson in 20/21secs on a good surface X 4..
When you come off the slide & the rear hooks up.. You can feel the frame trying to tie it self in knots.. one of the main
reasons they wobble in a straight line...

Had a Briggo Jawa / MK3 Weslake way back when..

hells bells

they were using an Enfield clutch , and a poorly designed frame ,

Damn

Stephen

ps the Enfield clutch is actually a clever design !

[ducatilover]

Right you clever buggers
Question/scenario thing

I have a plan, change my firing order to a "medium bang" set up.
Current is a typical flat plane crank (ZZR600D), waste spark and carbs
What I'm planning: 1&4 fire together, then 2/3 as normal.
So it'd be 1/4-2-nothing-3, repeat.

Reason, coz I want to.

The best idea I have seen so far has been the #4 lobes off, machine down the cam shaft then put it back together with the new timing by press fitting the two parts in a sleeve. (like an RC30 cam)

Now...
How tight am I wanting the sleeve,
Slightly smaller I/D than the O/D of the cam? Then heat it...lots...and press 'em together (in a jig to get timing right)

I also considered vaing a small keyway in the cam and sleeve to allign it, but I'm concerned it may weaken the sleeve.

Help an idiot out, for a choccy fush.

I've been chatting to Bogan about it, but he hates 4cyls, so he's probably wanting me to do it and explode my motor so I have to buy another Bros650...

I'm also aware that the added effort to turn 1/4 over on the cimp stroke may be detrimental to the starter...or it may simply not have enough juice to turn over.

[bogan]

I've been chatting to Bogan about it, but he hates 4cyls, so he's probably wanting me to do it and explode my motor so I have to buy another Bros650...

Quite the opposite, gotta keep your grubby mitts of all the bros' by keeping you busy with the beige stuff

I think, trying the heat method is worth a go, but also worth having a nice press available if it sticks and cools. Cos the smaller the shaft the less clearance you get for a given temperature rise (and the quicker the thermal transfer).

It'll be easy enough to machine up some holders for the lobe profiles with the required angular offset so they can just be slid along a bit of RHS as it is assembled, might even be just as easy to setup as a keyway anyway; and gives a better finished unit.

Also, don't worry about the starter, it'll be a case of what goes up must come down, harder to compress but then it'll put back a lot of that force on the downstroke... failing that, just call Ed!

[ducatilover]

Righto- may employ you sometime this year to make the jiggy-thing. I have access to a few places in Palmy with heat/press, so we should be sorted.

I'm pretty sure I had some spare cams floating around at home, but may use the opportunity to get the late model ones I need

[Ocean1]

What's the cam made out of?

And giz a pic, eh?

[ducatilover]

Not sure, probably cast iron, and I like the sleeved idea more than welding (that scares me)

I'll attemp to get a pic from teh googles, or try find the set of cams I have at home
Being external oil feed I could even run a sleeve inside?

[Ocean1]

Not sure, probably cast iron, and I like the sleeved idea more than welding (that scares me)

Probably SG iron. Easy check: http://igor.chudov.com/manuals/Spark...ery_Metals.pdf

Can be welded fairly reliably but sleeving it carefully means you don't have to remachine journals. Measure up the clearance around the non-machined part of the shaft, reckon you want about 6mm wall thickness for a sleeve. If you've got the gear you can key the shaft/sleeve, but it'd want to be nice and shallow. You could also taper pin the sleeve through the shaft, and peen the small end. The sleeve wants to be 4140 or similar, probably 0.025 inteferance. Test warm sleeve before assembly to make sure you can get it up to size/size or you won't get it on.

Being external oil feed I could even run a sleeve inside?

Much lower torsional strength, though. I'd stick with external sleeves even if you have to machine the shaft down a couple of mm to make room for them.

Do you need to worry about assembling the completed item?

[husaberg]

Probably SG iron. Easy check: http://igor.chudov.com/manuals/Spark...ery_Metals.pdf

Can be welded fairly reliably but sleeving it carefully means you don't have to remachine journals. Measure up the clearance around the non-machined part of the shaft, reckon you want about 6mm wall thickness for a sleeve. If you've got the gear you can key the shaft/sleeve, but it'd want to be nice and shallow. You could also taper pin the sleeve through the shaft, and peen the small end. The sleeve wants to be 4140 or similar, probably 0.025 inteferance. Test warm sleeve before assembly to make sure you can get it up to size/size or you won't get it on.



Much lower torsional strength, though. I'd stick with external sleeves even if you have to machine the shaft down a couple of mm to make room for them.

Do you need to worry about assembling the completed item?

What he is wanting to do is fairly common with the triumphs and Nortons and BSA's (ie screwing with the firing order)for the 90 degree cranks there is few web sites....
i had an idea they were moded with a spline (but probably miles of) I'm not no engineer

[ducatilover]

Probably SG iron. Easy check: http://igor.chudov.com/manuals/Spark...ery_Metals.pdf

Can be welded fairly reliably but sleeving it carefully means you don't have to remachine journals. Measure up the clearance around the non-machined part of the shaft, reckon you want about 6mm wall thickness for a sleeve. If you've got the gear you can key the shaft/sleeve, but it'd want to be nice and shallow. You could also taper pin the sleeve through the shaft, and peen the small end. The sleeve wants to be 4140 or similar, probably 0.025 inteferance. Test warm sleeve before assembly to make sure you can get it up to size/size or you won't get it on.



Much lower torsional strength, though. I'd stick with external sleeves even if you have to machine the shaft down a couple of mm to make room for them.

Do you need to worry about assembling the completed item?

Thanks heaps mate! I'll try the spark test with a set of cams, then I'll measure it up and go from there
I'm now worried about the clearance between the shaft and the oil feed system with a sleeve on it, but I'll tackle that when I can get to the bike (next week)

No need to worry about assembling it. I can see external will be stronger anyway.

Should be an interesting project... Better for my life span than boosting it

[ducatilover]

What he is wanting to do is fairly common with the triumphs and Nortons and BSA's (ie screwing with the diring order)for the 90 degree cranks there is few web sites....
i had an idea they were moded with a spline (but probably miles of) I'm not no engineer

Cool, I'll have a looky and see what I can find about them!

As long as whatever I do is safe with revs (ZX6 pulls 15k, I can drop the limiter to 10k, but that's gay)

[Ocean1]

Thanks heaps mate! I'll try the spark test with a set of cams, then I'll measure it up and go from there

Actually those graphice are shite, see if you can google up some better spark pictures. Videos even...