The Two Or Four Stroke Debate

[smalley250]

I raced enduro so my reference was to the enduro, but regarding trials no top uk riders i know of ride them. They cannot compete on cost n weight plus maintenance.

How many new 4rt do you see nowdays compared to the release of them. Beta`s seem poor as a friend of mine runs a 4rt and Beta 300 which stalls easy then a pain to start unlike the 4rt.

The 4 stroke will fade as new models prove this with no investment into 4 strokes.

[fivemeister]

Beta`s seem poor as a friend of mine runs a 4rt and Beta 300 which stalls easy then a pain to start unlike the 4rt

garbage

[_g_]

Funny really as I started out racing on club circuits road racing and the 2 strokes over a season cost a lot more to maintain than 4 stroke did. So suppose it depends on the sport really.

I suspect though you're thinking about production 4 stroke machines versus competition 2 strokes?

And presumably not in classes where the two are trying to compete on fairly equal grounds.

I've seen cases of GP 250s doing pretty well in powerbike races at some tracks - if you had a capacity limited 4 stroke racing against the 250s, I suspect the 4 stroke would cost a lot more.

[dgshannon]

garbage

My sentiments exactly.

[jse]

Beta`s seem poor as a friend of mine runs a 4rt and Beta 300 which stalls easy then a pain to start unlike the 4rt.

The 4 stroke will fade as new models prove this with no investment into 4 strokes.

My guess it that it's a maintenance problem directly related to that particular bike. All the Beta four-strokes I've come

across have been easy starters and essentially trouble-free.

I think that it's difficult to compare the reliability/maintenance schedule of the four-stroke used in Trials to that of the

much more stressful environment of MX and Roadrace. The oversquare (bigger bore than stroke) design used now does

not lend itself to a lot of piston skirt surface area so one has to be careful as to piston replacement intervals. The much

higher RPMs encountered in other forms of motorsports does make it rough on the slipper-type pistons and when the skirt

wears beyond service limit (the skirt is fairly short), it leads to "piston rock" which will cut a gouge at the upper, front part

of the cylinder (the "thrust side") and the cylinder will need to be replaced.

With the lower RPMs encountered in Trials, I would think that, with proper maintenance, the four-stroke will have an extended

life when compared to other four-strokes in other forms of competition.

Jon

[neo]

Some interesting points here gents

Let say (for instance) that MX went 100% 4T. Would that make 2T trial motors expensive to buy for the engine manufactures?....As the 2T volumes would drop like a rock wouldn't they.

Hey Jon.....can you shed some extra light to what happened to the GG 4T?....It looked so close ....yet now so far

Best of balance.

Neo

[nigel dabster]

Some interesting points here gents

Let say (for instance) that MX went 100% 4T. Would that make 2T trial motors expensive to buy for the engine manufactures?....As the 2T volumes would drop like a rock wouldn't they.

Hey Jon.....can you shed some extra light to what happened to the GG 4T?....It looked so close ....yet now so far

Best of balance.

Neo

So remind me which trials 2t motors go in mx bikes?

The radical idea of a sidevalve failed to produce enough power so i guess the idea is shelved.

[neo]

So remind me which trials 2t motors go in mx bikes?

Well apart from the link between Beta/KTM engine development, none as you know Nigel. But my point is if 2T's motors are only a very small part of the overall engine market that's bound to drive their price up.

So staying with my scenario above I guess small time engine manufactures would still be happy to make a 2T motor for Trials but how would that effect the price and how much engine development would go on?

Just discussing a hypothetical

Best of balance.

Neo

[ham2]

garbage

I think you and DGShannon are both being a little harsh on the Evo...I'm sure it has some redeeming features...I just can't think of any at the mo'

[jse]

Hey Jon.....can you shed some extra light to what happened to the GG 4T?....It looked so close ....yet now so far

Best of balance.

Neo

I haven't heard of anything lately. Last I knew, they had hired another design engineer, from France as I remember,

and were changing valve size and sparkplug placement in the head,

both very critical in a sidevalve engine. The plug placement is important due to the combustion chamber shape and

size and where the plug is located will determine flame front propagation and burn pattern. When I raced the sidevalves

in the 50's, we tried to treat the piston crown as one large squishband. The area over the valves is a constant due to

having to have the clearance for the valves to open. The little buggers could make a bunch of power if they were built

correctly.

I'm handling tech inspection at the U.S. National this weekend so I'll try to collar Dale and find out the latest on it's development.

My guess is the problem was the economy rather than technical difficulties. Should work well if properly developed and I understand the

engine only weighed a kilo or two more than the 2T Pro.

Jon

[b40rt]

I haven't heard of anything lately. Last I knew, they had hired another design engineer, from France as I remember,

and were changing valve size and sparkplug placement in the head,

both very critical in a sidevalve engine. The plug placement is important due to the combustion chamber shape and

size and where the plug is located will determine flame front propagation and burn pattern. When I raced the sidevalves

in the 50's, we tried to treat the piston crown as one large squishband. The area over the valves is a constant due to

having to have the clearance for the valves to open. The little buggers could make a bunch of power if they were built

correctly.

I'm handling tech inspection at the U.S. National this weekend so I'll try to collar Dale and find out the latest on it's development.

My guess is the problem was the economy rather than technical difficulties. Should work well if properly developed and I understand the

engine only weighed a kilo or two more than the 2T Pro.

Jon

Hi Jon

What side valves did you race ?

Harley Davidson ?

Ross

[fivemeister]

I think you and DGShannon are both being a little harsh on the Evo...I'm sure it has some redeeming features...I just can't think of any at the mo'

No, I meant what he SAID was garbage - the Beta Evo 4T is a brilliant bike!

[jse]

Hi Jon

What side valves did you race ?

Harley Davidson ?

Ross

Ross,

A little with the Harley's, but a lot with the V8 Ford/Merc's Hudson Hornet's etc., including the little Ford V8-60 used in mini-sprints

of the time. For top-end HP, it was hard to beat the overheads as I found with an ARDUN conversion for one of the flatheads

I built. As I remember, Zora Arkus (father of the Corvette) built the ARDUN conversions for trucks at the time but we soon found

they were a welcome addition for power-hungry geeks like me.

I would imagine the V8-60 is fairly rare nowadays, I think they only made them for a year or two in the

early 40's.

Ah, the good ole days (actually things are a LOT better now!).

Jon

[ham2]

No, I meant what he SAID was garbage - the Beta Evo 4T is a brilliant bike!

I know, I was just yankin yer chain

[b40rt]

Ross,

A little with the Harley's, but a lot with the V8 Ford/Merc's Hudson Hornet's etc., including the little Ford V8-60 used in mini-sprints

of the time. For top-end HP, it was hard to beat the overheads as I found with an ARDUN conversion for one of the flatheads

I built. As I remember, Zora Arkus (father of the Corvette) built the ARDUN conversions for trucks at the time but we soon found

they were a welcome addition for power-hungry geeks like me.

I would imagine the V8-60 is fairly rare nowadays, I think they only made them for a year or two in the

early 40's.

Ah, the good ole days (actually things are a LOT better now!).

Jon

Hi Jon

I was surprised to read about racing side valves as I had been lead to believe that they were more of an industrial engine.

Whar are the limiting factors of S/V engines ?

Ross