The 50

[TZ350]

Kel called around today with his arm in a cast, broken bone in his hand and elbow, 6-8 weeks before the cast comes off, so just in time for the start of the North Island Series.... ..... well hopefully.

The engines symptoms looked the same as Taupo and Kaitoki where the ignition was wrong and I felt very depressed thinking I still hadn't got a handle on this TPS and 3D ignition mapping thing.

There were suggestions (not from Kel) that I should de tune it a bit to make it more reliable and I was tempted until I thought about it and realized that 100% of F4 2-Strokes that have failed when racing all made less than 31hp.

In fact the last blowup reported the other week in another thread was a 14rwhp 125, so the idea of de tuning for reliability is dumb. The right thing to do is develop the reliability of this engine and at 9 bar clearly this engine is not all that stressed, and I should be able to push that up to 10 or possibly 11.

Attachment 268503 Attachment 268504

Took the head off and it turns out that the modification I had done to the piston so the ring gap ran in the boost port for improved reliability was the problem. The pin had come out and jammed the ring and piston.

Attachment 268500 Attachment 268501 Attachment 268502

So shot ourselves in the foot again but in a different and more imaginative way this time, sorry Kel.

Now does anyone know what the realistic upper BMEP number is for an air cooled 2-stroke because I would like to go there?

I had tried to copy the Yamaha TZ style of ring peg where the pin came down from the top and the tip was bent into a small hole below the ring land. It all looked good on my piston but I think the vibration of the piston slapping about at 14K broke the tip off of the SS welding wire pin, piano wire next time.

[mr bucketracer]

I think our problem was the type of wire I used for the pin. I used SS welding wire and I think it fractured, it probably would have worked if I had of used piano wire instead.

i just cut the pins out the old pistons think they have a taper to long ago to remember . anyway i thought kel always has it sideways lol

[RMS eng]

i just cut the pins out the old pistons think they have a taper to long ago to remember . anyway i thought kel always has it sideways lol

we used pins from a needle roller bearing,heat the piston and press fit in ,as the are hard,bearing shops sell them .

chris

[jasonu]

we used pins from a needle roller bearing,heat the piston and press fit in ,as the are hard,bearing shops sell them .

chris

or use the drill bit...

[mr bucketracer]

or use the drill bit...

don't think a big ass wood drill will work lol maybe a parallel shank drill will

[cotswold]

I have found these over in Sweden, they look pretty good but just means I will have to develop my spare cylinder as my ported one is too big for these at 40mm.
Honda Racing 39 mm PE-80

A special flask designed by BARIKIT for racingendamål Fits Honda MB / MT engine family who want to run 50cc.

The pistons are in several tolerances starting 38.95,96,97, 98.
Super nice piston complete with all parts.
Overall Height 51.40 mm.
Height to the piston edge 50.20 mm
Chromring 1 mm height.
Piston pin 12 x 31.40 mm.
Piston Ring Locking straight back 180 degrees.
Center bolt to the piston top edge 26.10 mm.
Center bolt to the lower piston edge 24.10 mm.

Order Number PE-80 + size

The Rod kit looks beautiful but have been informed would be outside the rules so bought an aftermarket one ( though I cannot see race part written on the box anywhere ? )

[husaberg]

I have found these over in Sweden, they look pretty good but just means I will have to develop my spare cylinder as my ported one is too big for these at 40mm.
Honda Racing 39 mm PE-80

A special flask designed by BARIKIT for racingendamål Fits Honda MB / MT engine family who want to run 50cc.

The pistons are in several tolerances starting 38.95,96,97, 98.
Super nice piston complete with all parts.
Overall Height 51.40 mm.
Height to the piston edge 50.20 mm
Chromring 1 mm height.
Piston pin 12 x 31.40 mm.
Piston Ring Locking straight back 180 degrees.
Center bolt to the piston top edge 26.10 mm.
Center bolt to the lower piston edge 24.10 mm.

Order Number PE-80 + size

The Rod kit looks beautiful but have been informed would be outside the rules so bought an aftermarket one ( though I cannot see race part written on the box anywhere ? )

Did you see his Derbi cylinder and off the shelf rotary valve conversion plate?

[cotswold]

Did you see his Derbi cylinder and off the shelf rotary valve conversion plate?

I have spent a decent amount of time going through his web site and these boys are too clever by half.

Do you have an opinion on the legality of that rod kit? It's about triple the cost of the Japanese one that turned up today.

[husaberg]

I have spent a decent amount of time going through his web site and these boys are too clever by half.

Do you have an opinion on the legality of that rod kit? It's about triple the cost of the Japanese one that turned up today.

I Have learnt to have no opinions on Rods what so ever..........

[F5 Dave]

Ha, yeah I think we did the rod thing to death & I've kinda lost interest in thinking about it. I do know std Yam stuff is pretty damm fine. pity they use 16mm pin in their bigger stuff.

Center bolt to the piston top edge 26.10 mm is the only average thing I see there, actually maybe it isn't that bad. Looks like a good setup ring wise & that's most of the battle.


What I have learnt is Long brand rod kits used to have crap bearings in them. I'd buy genuine MB50 bearings (if they are the same for yours) as I seem to remember they got superceeded by the CR part, but that now listed as MB part is super legal.

[mr bucketracer]

where do i get a rod kit for a tf 100 ?

[F5 Dave]

Phil Turnbulls; but you'll have to get in a time machine,

[husaberg]

Ha, yeah I think we did the rod thing to death & I've kinda lost interest in thinking about it. I do know std Yam stuff is pretty damm fine. pity they use 16mm pin in their bigger stuff.

Center bolt to the piston top edge 26.10 mm is the only average thing I see there, actually maybe it isn't that bad. Looks like a good setup ring wise & that's most of the battle.


What I have learnt is Long brand rod kits used to have crap bearings in them. I'd buy genuine MB50 bearings (if they are the same for yours) as I seem to remember they got superceeded by the CR part, but that now listed as MB part is super legal.

I see also the CR80 big end (aircooled i think) part number is the same as a NH125 lead too(maybe always was). Maybe Honda is indeed the Devil.
What actually was Mikes "Wraparound avatar rod" cause it sure was mallable.
50mm pistons are a pain its a shame Ken Seeber can't whip up some.......
I think the crankpin in the CR80 Air cooled was the same as the MB50 but had an odd maybe 13mm pin

[cotswold]

[QUOTE=F5 Dave;1130698982]Ha, yeah I think we did the rod thing to death & I've kinda lost interest in thinking about it.



I missed that, where was this discussed and how does one know what is illegal and what is after market ?

[Bert]

Phil Turnbulls; but you'll have to get in a time machine,

Incorrect Dave.
Phil has re opened and secured the Suzuki franchise.



No time machine needed.