Bucket development: A few questions for the wise ones

[Bert]

Hi all.
I been slowly building up a new F4 100cc two stroke bucket motor (first new motor in at lease 10 years) and I've got a few questions regarding:

1. Sparkplugs, Standard spark-plug (NGK B9EGV or NDw29ES*) thread lengths are normally 3/4" long, has anyone found a 14mm pitch racing plug that is in the same heat range (~NGK 9-10) that has a longer thread (lets say ~22mm, I recall something about tz125s & rotaxs kart motors having longer threaded plugs, so temp sensors could be installed)?
(reason: I'm figuring out the best way to profile my head). I've download the NGK catalogue but can't seem to find anything useful.

2. Carbs, Do early RGV (1988-90ish) require vacuum pressure or pressurised air-box to work correctly? (reason, I've got a box of carbs but the RGV fits the best).
Was planning on sleeving it down to 30mm. any help on these carbs would be great (I've spend hours looking/googling for information on these to no avail, so its time to ask).

3. Rubber engine mounts, I've done a little bit of work to mount the engine directly to the swingarm pivot, so now I just need to make some new rubber bushes. This is not looking like an off the shelve solution, so I'm going to need to make something up. I was thinking about some rubber hose with a steal insert (which the swingarm bolt go's through); but I'm not sure if hose will be dense enough or even be suitable. any thoughts ??

cheers in advance.

Brent

[schrodingers cat]

Hi all.

3. Rubber engine mounts, I've done a little bit of work to mount the engine directly to the swingarm pivot, so now I just need to make some new rubber bushes. This is not looking like an off the shelve solution, so I'm going to need to make something up. I was thinking about some rubber hose with a steal insert (which the swingarm bolt go's through); but I'm not sure if hose will be dense enough or even be suitable. any thoughts ??

The bush type you are decribing is known as a 'metalastic' bush.
Rubber hardness is expressed in 'Shore' numbers. The bigger the number, the harder the rubber. Usually this type of bush has a shore number of 80 or 90.
Your homemade hose bush would be lucky to achieve Shore 50. Better if you were able to crush the hose.


Get hold of The Mount Shop and have a look at their catalogue. There are all sorts of weird and wonderful things you may be able to adapt.
Otherwise look at Stocks range of Urethane bushings

[bucketracer]

3. Rubber engine mounts, I've done a little bit of work to mount the engine directly to the swingarm pivot, so now I just need to make some new rubber bushes. This is not looking like an off the shelve solution, so I'm going to need to make something up. I was thinking about some rubber hose with a steal insert (which the swingarm bolt go's through); but I'm not sure if hose will be dense enough or even be suitable. any thoughts ?? cheers in advance. Brent

Early TZ's came from the factory bolted up in the normal way at the rear mounting points and with metalastic bushes in the front. The top rear mount used to rip off and the frame crack around the lower rear engine mount. The cure was to discard the top rear mount and fit nolathane or metalastic bushes to the lower rear mounts.

Rubber hose and a steel bush, remember this is buckets and your allowed to explore any solution you like, if the rubber area of the bush is a lot longer than a normal metalastic bush, it might give the engine enough support to work.

[bucketracer]

2. Carbs, Do early RGV (1988-90ish) require vacuum pressure or pressurised air-box to work correctly? (reason, I've got a box of carbs but the RGV fits the best).
Was planning on sleeving it down to 30mm. any help on these carbs would be great (I've spend hours looking/googling for information on these to no avail, so its time to ask).
cheers in advance.

Brent

Are RGV carbs slightly down draft? as I think Chambers has an early 32mm RGV carb on his 22.5 rwhp GP100, it works just fine, I will see if I can find a picture for you to check, so you can see if its the same as yours.......

[bucketracer]

1. Sparkplugs, Standard spark-plug (NGK B9EGV or NDw29ES*) thread lengths are normally 3/4" long, has anyone found a 14mm pitch racing plug that is in the same heat range (~NGK 9-10) that has a longer thread (lets say ~22mm, I recall something about tz125s & rotaxs kart motors having longer threaded plugs, so temp sensors could be installed)?
(reason: I'm figuring out the best way to profile my head). I've download the NGK catalogue but can't seem to find anything useful.

cheers in advance.

Brent

Found this here:- http://www.two-strokes.com/forums/in...5-spark-plugs/

old = R6120-105 = R7282-105 = new => short insulator, thread dia 14 mm X 19 mm, spanner 16 mm,

e.g. Deto: R6120A-105 = R7282A-105 => thread dia 14 mm X 22 mm, spanner 16 mm, no gasket for deto counter

old = R6385-10 = R7376-10 = new => long insulator, thread dia 14 mm X 19 mm, spanner 20.8 mm

R7376B-10 => thread dia 14 mm X 22 mm, spanner 20.8 mm

PDF of NGK racing plugs here:- http://www.elit.cz/Files/ObrazkyPMod...gplugs_ENG.pdf

[Bert]

Get hold of The Mount Shop and have a look at their catalogue.

Nice feedback guys. already some solutions. Thanks a lot.
Bucketracer, yes it is the same carb; so that said; it is safe to assume that it doesn't require either. just put it in and away we go... (well sort of).
Sparkplugs ouch, $$$, o'well its the price you pay for building silly things.

[=cJ=]

You can also go the sikaflex way for your rubber mounts, you just have to get an inner and outer bit of steel tube, then fill the gap.

Have a look here, the GT-4 guys also used it heaps.

http://www.toymods.org.au/forums/showthread.php?t=24675

[jasonu]

No need for rubber mounting if you do a proper job and your engine isn't a 'shaker'. The motor in the pic is totally solid mounted, it runs smooth with no vib problem in the pegs or bars and has never broken or cracked the frame.

[schrodingers cat]

You can also go the sikaflex way for your rubber mounts, you just have to get an inner and outer bit of steel tube, then fill the gap.

Have a look here, the GT-4 guys also used it heaps.

http://www.toymods.org.au/forums/showthread.php?t=24675

If you keep looking down the post there is some other interesting info

Hardness scale

Rubber band 25-35
Light car tyre 60-65
Tap washer 85-90
Heavy track tyre 95-100

Standard engine rubber mount 40-50
Noltec polyethylene bushes 80-85

From what I can see on the web, material with 70 to 80 hardness will be a good place to start.

As to the material choice.

Sikaflex does not seem to be the right material for the purpose.
It is primarily a sealant, and it’s hardness is 23-27, which is very low.
http://www.sika.com.au/home/cmc/cmc/...lexPRO_tds.pdf

Devcon’s Flexane 94 seems to be a good product, however with claimed hardness 97, I would not use it.
The harder the better is not the case – cracks in metal may be the result.
The softer version, Flexane 80, has hardness 87, which is still a bit high.
There is an add-on flexibiliser (what a word ) which lets you to lower the hardness.
http://www.devcon.com/techinfo/153.pdf
The good thing is you can do different hardness bushes from the same set of chemicals, so no waste.

So in fairness the sikaflex method is a band-aid.

I think JasonU is correct re solid mounting SO LONG AS your frame is sufficiently rigid and the casings you're attaching to are sufficiently strong.
THe last thing you need is critical areas of the engine getting distorted under load. 'Stressed' engines are designed to spread these loads in a predictable manner.

If yu're not generating a whole heap of grip and havn't got a berzillion HP then it is all a bit academic

[Bert]

No need for rubber mounting if you do a proper job and your engine isn't a 'shaker'. The motor in the pic is totally solid mounted, it runs smooth with no vib problem in the pegs or bars and has never broken or cracked the frame.

If you keep looking down the post there is some other interesting info

I think JasonU is correct re solid mounting SO LONG AS your frame is sufficiently rigid and the casings you're attaching to are sufficiently strong.
THe last thing you need is critical areas of the engine getting distorted under load. 'Stressed' engines are designed to spread these loads in a predictable manner.

.... berzillion HP then it is all a bit academic

Great feedback guys.
Maybe this is being over cautious, not having not actually had the motor running yet, I'm not sure if she will be a shaker or not (given the balancing work done thus far, she shouldn't be). The engine mounts/casings look like they have been designed with stressed member mounting in mind, so hopefully I havent gone down the wrong path with this...

But having destroyed my share of mounts and frames over the years; I thought it prudent to at lease try and do the job right to start off with.. As I suspect this might be my last build for some time (wifey issues) so I really want it to last.

[marsheng]

As you are using long plugs, mill the plug recess down by 2-3 mm. Then you can use standard plugs rather than special ones for the life of the motor. If you remove the thermocouple later, replace it with a 2 mm aly washer. Cheers

[F5 Dave]

Hi

With that engine you should be fine, but a TS/TF motor designed to run at 6000 rpm around a sheeptrack then asked to do 11,000 vibrates like a , . . .well I'll let someone deviantly filthy (like Jason) complete the analogy.

RGV carb should be fine on a hot 100 pulling revs, I wouldn't sleeve it. I have one of those on my 100. Later model RGV carbs should be avoided (solenoids etc).

[speedpro]

Use a B9(anything) plug. You can waste money on flash ones but my own personal experience says they don't melt before the piston and they foul up just as quick. My TS used to chew through plugs for some reason even with the same ignition I had/have used on other engines with no problems. No difference on the dyno either, I've checked.

I've used the same 32mm Mikuni roundslide carb for lots of years. It's way big enough. I had a 28mm Keihin semi flatslide on the MB sidecar and it was fine as well. So again from personal experience, anything in that range should be workable. 34mm might be tempting but it's a bit big I think.

Solid mount it, and I mean SOLID. Rebalance the crank, no science involved just press a slug of aluminium into each of the larger holes in each crank wheel. It works, I've done it. I've played with the engine mounting problem as well. Those TSs will vibrate your frame to bits if you don't get it right. If it is free to move at all it will sort of resonate. Tied into the frame it can't

[Bert]

've used the same 32mm Mikuni roundslide carb for lots of years. It's way big enough. .... 34mm might be tempting but it's a bit big I think.
Solid mount it, and I mean SOLID. ..... Those TSs will vibrate your frame to bits if you don't get it right. If it is free to move at all it will sort of resonate. Tied into the frame it can't

Cheers Speedpro & F5dave,
Maybe I should have shared what new engine is in development;
I've got a little TZR125, which is now a TZR100 (photos and the story on its way soon) same as Busa Petes new toy.

Given the comments, solid mounting looks like the solution (at lease a start). So I'll make up some low density nylon bushes and work up from there.

I measured up the RGV carbs; its 33.5 mm? (yes they looked modified), so hummm I might keep looking through the boxes.

Thanks guys

[F5 Dave]

Yeah I remembered what you said you were building & it will vibrate less than the TS fer sure. 33.5 huh? Well it was a 'production' bike & no one ever cheated on those. . .