ESE's works engine tuner

[Pursang]

I've got back into Trials. And bothered to read the spec of my new bike. Which is industry standard.

250cc. Bore 72.5. Stroke 60mm! So the other way around, and these are not high revving (or high power) engines.

The 280s and 300s keep the same stroke. Ok these are low BMEP engines with hardly a conventional pipe, but it seems odd that they would be so short stroked.

It was 'Industry Standard in the Sixties and Seventies too! Bultaco Sherpa T.

The stroke was inherited from the original 125cc engines.

It was the same in Metralla road bikes, Pursang MX and TSS roadracers. The 60mm stroke was used in Bultaco engines up to 325cc.

[Grumph]

It was 'Industry Standard in the Sixties and Seventies too! Bultaco Sherpa T.

The stroke was inherited from the original 125cc engines.

It was the same in Metralla road bikes, Pursang MX and TSS roadracers. The 60mm stroke was used in Bultaco engines up to 325cc.

Once you'v e got a boring machine set up to do the job on that center, the design department tends to use what is already there. If that happens to be your only boring machine as I'm sure was the case with some of the smaller outfits, then everything gets designed around that. You may also have a stock of crank forgings of the size needed for that stroke. Got to pay for that tooling.

I read in one of Phil Irving's books that the stroke of the Velocette Roarer came about because the factory had just taken delivery of a Heald Bore-matic machine.
One of the settings was fairly close to what they had wanted so that's what got used.

[husaberg]

Once you'v e got a boring machine set up to do the job on that center, the design department tends to use what is already there. If that happens to be your only boring machine as I'm sure was the case with some of the smaller outfits, then everything gets designed around that. You may also have a stock of crank forgings of the size needed for that stroke. Got to pay for that tooling.

I read in one of Phil Irving's books that the stroke of the Velocette Roarer came about because the factory had just taken delivery of a Heald Bore-matic machine.
One of the settings was fairly close to what they had wanted so that's what got used.

One of the mags i was reading that came from you the other day had the Irving twin (model O of similar concept to the Roarer that used a heap of parts from other road velos, i never knew he designed the adjustable top shock mount either but makes sense in hinsight it was him.

[Pursang]

Love to give one of these some two stroke hindsight 'updates'.

[Frits Overmars]

Love to give one of these some two stroke hindsight 'updates'.

Don't.
I was approached in a similar situation by a friend who wished to 'update' his factory MZ racers. They were not very reliable 55 years ago with 30 hp per cylinder. They really don't need the extra 10 hp per cylinder that we could add today without much effort.
At the time, the factory constructed a new eight-speed gearbox three years in a row. I suppose they did not do that because the first version was so reliable. And I'm afraid the latest version wasn't either.
Then there was the engine cooling, or rather the lack of it: thermosyphon cooling, which I usually refer to as thermosyphilis cooling. A coolant temperature of 90°C was not unusual so it shouldn't surprise you that the pistons had an extremely short life.
Leave those old machines in their former glory. They are suitable for demos, not for competition any more.

[Pursang]

Don't.

Don't..try this at home! Thank you Frits, for the sane, sensible, experienced, voice of reason.

I do understand and accept the need to not over-challenge the vintage mechanicals... but....with a shed full of 50 -80 y/o projects and now, finally, some time to play with them, the path of the factory faithful restorer (cough, spit) is not for me!

I appreciate every piece of of technical advice, tips, warnings that have been shared here. Thank-you everyone.
May the wisdom contained in this thread and the others, be available forever.

Cheers, Daryl.

[katinas]

Another thermo-symphony, Dave Simmonds Kawasaki 125 and Guy, what a happy guy. https://www.paddock-gp.com/people-a-...he-guy-coulon/

[Grumph]

Here's an unusual question for the hive mind.
I find myself in posession of three cylinder heads for the current project.

A genuine toroid shape. With squish band. Plug is dropped into the chamber slightly as it should be.
A head with squish and a central cylindrical shape with basically square edges and a flat roof.
A head with the current conventional squish and part spherical chamber

Initially I'll be aiming for around 12:1 compression. No significant difference in fin area between them. All are central plug.

Which is the favourite ?

[husaberg]

Here's an unusual question for the hive mind.
I find myself in posession of three cylinder heads for the current project.

A genuine toroid shape. With squish band. Plug is dropped into the chamber slightly as it should be.
A head with squish and a central cylindrical shape with basically square edges and a flat roof.
A head with the current conventional squish and part spherical chamber

Initially I'll be aiming for around 12:1 compression. No significant difference in fin area between them. All are central plug.

Which is the favourite ?

i knbow you were thinking reed but
just saying

http://progress-is-fine.blogspot.com...hs-merlin.html
the later one which peter crew raced was as far as i remember starmaker based.
paging neil...

[Grumph]

i knbow you were thinking reed but
just saying


the later one which peter crew raced was as far as i remember starmaker based.
paging neil...

No I've seen the articles on them and none were Starmaker based. You're the one with a binful of Villiers crankcases - and a Greeves barrel, lol.
There actually was a disc valve converted Villiers here in ChCh late 60's. Built in the University workshops. Came out 2 or 3 times and disappeared.
I suspect the lack of the now common Japanese rod kits and low expansion pistons meant it was prone to meltdowns.

[F5 Dave]

Well the answer is quite simple.

On the middle cylinder run the Toroidal, on the left cylinder the conventional, on the right cylinder. . Well you get the picture.


Glad to be of help.

[Grumph]

Well the answer is quite simple.

On the middle cylinder run the Toroidal, on the left cylinder the conventional, on the right cylinder. . Well you get the picture.


Glad to be of help.

Thanks Dave. i don't quite have the bits to build a triple. I will admit to feeling slightly inadequate there, I'm aware there are people on here who would not let that stop them.

[F5 Dave]

More power to you that you are still spinning spanners. Presumably in the laundry.

[husaberg]

No I've seen the articles on them and none were Starmaker based. You're the one with a binful of Villiers crankcases - and a Greeves barrel, lol.
There actually was a disc valve converted Villiers here in ChCh late 60's. Built in the University workshops. Came out 2 or 3 times and disappeared.
I suspect the lack of the now common Japanese rod kits and low expansion pistons meant it was prone to meltdowns.

I will have to look for it in the pile unless someone has it handy?

My recollection was the original was very much greeves based but the later looked more starmaker like and even had one o f those 6 speeds added.
Crew ended up with a few incl a 350 but eiter sold or stopped racing them about 10 years ago.
i found a FB page that looks to be hois but it only has TZ and Manx plus nothering before 2012.

[wobbly]

A toroid will win hands down , but that only " works " when pushing the envelope , and at 12:1 that hardly defines pushing anything.