ESE's works engine tuner

[husaberg]

IHusa was of course exaggerating about the piston mileage in the Yamaha TZ250G but apart from that I must agree with him on all accounts.
The TZ250G was remarkable. Power-wise its cylinder block was a big step forward, with better transfer ducts, smaller exhaust duct volumes and the huge inlet ports that were detrimental to piston life.
The following year Yahama reversed the direction of crankshaft rotation by means of the jackshaft, but we'd already found a much simpler solution: we reversed the cylinderblock on the 'G': piston problem solved.

Although it might appear to be flippant, I actually wasn't Frits, it was out of McKellar’s Yamaha twins book, he lists 80-120 KM piston mileage and cranks not much more. With 53 Rear wheel hp 43mm inlet port width and a 4mm Sinusoidal port roof. More curving yet flat roofed transfers
Slightly larger Front forks were added as well.
The official recomended replacement of pistons on the G i believe was per race.
Along with the Jack shaft and the changed bore and stoke the H was also the first year of the PV, it has bigger big ends, lighter crank wheels and a different crankshaft coupling resulting in less crankshaft flex.
Base mounted cylinders 44mm intake port width 23mm ex port height and 55 HP. But of course more importantly much greater reliability.

Funny enough as you know yamaha, eventually followed you. (and MZ)

[Frits Overmars]

Here's a fresh KC blog, giving his 'big bang' appraisal. You may have to scroll down some, to the subject feature if it doesn't pop up
http://www.cycleworld.com/why-single...gion-2&lnk=img

Yet another link that didn't work for me. All I got was "The page you are looking for no longer exists". Is it just me or does this look familiar to you guys?

[trevor amos]

Yep, I got the same response Frits, so it`s not just you!

Wob, with VF2`s being rarer than chicken`s teeth, and VF3 not as good, what would your recommendation be for the next best thing in place of the VF2 for the Honda RS 125?

Cheers, Trevor

[adegnes]

My newly started "vlog" about the Spx etc.
Keep your expectations low.

[wobbly]

Yep, that page doesnt exist Frits.
Re the reeds for RS125.
I have done a huge test program on the SKUSA CR125 that makes near on the same power as the RS does.
The reed block is pretty much identical, but the big difference is that the CR inlet manifold is bent 30* to the left.
Thus I "rebend" the flow such that I get almost identical flow ( tested with a probe on a Superflow ) from each of the upper reed windows by using 3 different backups.
On the bottom a single blade works the best to help direct flow upward toward the piston.
I hope to get another test session in before the Vegas Worlds in November, so send me a PM and I will try to do a some runs with your block before I go.

[TZ350]

My newly started "vlog" about the Spx etc.

I love it, actually I like all the good discussions on here, but your blog and workshop is stuff I can relate too .......

[adegnes]

I love it, actually I like all the good discussions on here, but your blog and workshop is stuff I can relate too .......

Thank you!

[tjbw]

Yet another link that didn't work for me. All I got was "The page you are looking for no longer exists". Is it just me or does this look familiar to you guys?

I think this is the correct link:

http://www.cycleworld.com/why-single...e-good-in-dirt

[Frits Overmars]

Adegnes, I liked it a lot!

[adegnes]

Adegnes, I liked it a lot!

Thank you!

[twotempi]

Originally Posted by Frits Overmars t
IHusa was of course exaggerating about the piston mileage in the Yamaha TZ250G but apart from that I must agree with him on all accounts.
The TZ250G was remarkable. Power-wise its cylinder block was a big step forward, with better transfer ducts, smaller exhaust duct volumes and the huge inlet ports that were detrimental to piston life.
The following year Yahama reversed the direction of crankshaft rotation by means of the jackshaft, but we'd already found a much simpler solution: we reversed the cylinderblock on the 'G': piston problem solved.



I have a TZ250G with the inlet port about the same size as the bore. My solution was to weld a 6mm wide vertical bridge in the inlet port which was then shaped into an old cylinder that needed to be re-plated. Early days but this seems to give better support to the rear face of the piston to guide it down the correct hole .l My reasoning also included that since it was in direct line of the conrod there was little reduction in effective port area.

Reversing the cylinder would mean new pipes etc so this solution have the least effect on the rest of the bike. Also wanted the bike to look "original". Also managed to find a stash of 30 "G" pistons which are 54.25 mm rather than 54.00mm !! And no - I do not want to sell any.

Comments anyone ? ( Especially Frits Overmars )

[Hemi Makutu]

This may help: http://www.greencarcongress.com/2016...-anltribo.html

It may even assist with 2T engines with cylinder ports making a production road vehicle comeback,
if improved durability on lower oil consumption/HC emissions are part of the DLC tribofilm deal.

[wobbly]

I did the same trick of putting a bridge into the intake on a 350G - 6 port cylinder, as it now has reed boxes on the back.
This allowed a much wider intake width, and then I added an extra pair of boost ports up each side of the welded in bridge.
Works well.
Hummel and Chevalier did some cylinders for the 250 with a bridged intake that worked well also.

[lodgernz]

I love it, actually I like all the good discussions on here, but your blog and workshop is stuff I can relate too .......

Me too. Good stuff Alex.
It looks like you don't have a clutch on the variator or the driven pulley. Are you using the engine movement to act as a clutch?

[twotempi]

If you are only permitted to use fuel commercially available at the pumps does Gull Force Pro E85 fit this definition ?? 85% Ethanol / 15% Petrol

This is available at the Gull Forrest Hill direct from their forecourt fuel pumps as advertised on the Gull website and the roadside signage .

Also available from other Gull service stations as well.