PX221 - MHR very tuned - 38mm Dellorto
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Hooked
PX 200
Joined: 25 May 2016
Posts: 275

Sat Apr 03, 2021 8:27 pm quote
jimscoot wrote:
Hi Jack. Iíve noticed your using a helical cut gear primary.
Iíve always been confused as to what is the better option (pros, cons etc) between straight cut and helical cut gears, what are your thoughts on this?
Ran on straight teeth for a good 3 years installing it without understanding what I was installing at the time... I had the malossi 24/63 combo and needed to swap my clutch and primary out, so I thought why not...

Theres definitely more noise coming out of the primary and clutch, thatís with the full metal to metal contact...

When you cycle through the gears its a lot more crunchy with the engagement, but definitely more solid transmission of power... feels like thereís less dip in revs between gears.

I was quite comfortable cruising on short highway stints.

The primary seemed bulletproof, not much metal wear in the oil.

But eventually I went back to DRT helical stock gearing 23/65 the biggest reason because I wanted a shorter gear setup (higher gear ratio) and as far as I can see, thereís not that many short gear options for straight teeth clutch and primary (all race use I imagine)

So with helical you get less noise and a smoother, softer shift (which is better for me riding around the city)...

Just my none scientific experience, question hijack over...
Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 2755
Location: London UK
Sun Apr 04, 2021 12:12 am quote
jimscoot wrote:
Jack221 wrote:
Plenty of traffic here. Lockdown, Teir4 or not. Dodging it is half the fun.

For those in doubt whether a Cosa superstrong basket is worth the investment. Here is mine after 6 years, maybe 10,000 miles and with various tunes between 30 to 50bhp. Ridden like I stole it most of the time too.
Hi Jack. Iíve noticed your using a helical cut gear primary.
Iíve always been confused as to what is the better option (pros, cons etc) between straight cut and helical cut gears, what are your thoughts on this?
I really think it doesn't matter so much. Gearing in mine is total stock. 23/65 with 35 tooth. Helical is stronger and smoother but more friction and higher side load. Straight cut is kinder to the bearings but weaker. And so noisy. Like most things scooter, is personal choice and no right answer.
Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
Joined: 14 Jun 2017
Posts: 2755
Location: London UK
Sun Apr 04, 2021 12:29 am quote
charlieman22 wrote:
Thoughts from 50K feet.
- 4 post seize says heat expansion of piston vs cylinder studs.
- Failed WOT so fuel starvation or:
- Could be question of piston limits - those MHR are full of variating thickness. Any further work would only create more chance of piston deformation.
- Failure of oil delivery - but assume you are running premix
- Float bowl sucked dry? Longish WOT, hill that made carb at steeper angle. Have you played with float height recently for other purposes?

Putting breaks on gently - but due to piston swelling.
My only experience with piston swelling seizes are that they are immediate and unfriendly.
That kinda raises an eyebrow - its different at least.

Those would be on my list - and are probably already on yours...
The funniest thing about the seize was there are no detonation marks. Head still like new. Must have been too weak to pink properly. There was no sounds and it felt a bit dead over 80. While I was thinking 'this is weird' it seized. Can only be fuel starvation. That was the third time it had been over 80 that day. Was maybe just lucky before. Piston marks were straight overheat at the exhaust port. Usual for running weak.

It can only be something between tank and carb. There is a pump and two fuel filters and a load of pipes. Something wrong right there.
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