Walter Tritshe forged pistons

[Gary D]

Evening all!

I've also placed the enquiry below on the 500 forum, but so far no luck. Maybe someone has used the Walter Tritshe forged pistons on the 3 1/2 & can share their thoughts?

Has anyone had experience of using the Walter Tritshe 71 mm forged pistons for the 500? I'm curious to know how they compare with standard & whether any re-jetting was required? I also understand that the original bores were tapered from Morini? Is this type of boring service readily available & best used, compared to plain boring?

Any advice would be appreciated folks.

Cheers

Gary

[72degrees]

When I took my 350 cylinders to be rebored to take the max oversize 350 Vertex pistons NLM supplied (I wanted to keep below 350 for capacity class rule compliance so resisted a '375' conversion) I took the trouble of taking a printout from the manual mentioning the clearances and tapered boring. This is a very highly regarded place that does a lot of work for MX riders and racers, including getting re-plating done. Not sure if they acted on it as I didn't get to speak to the engineer who did the job, but the counter assistant who received the job said that all information would be useful as they hadn't done Morini cylinders before. The proof of the pudding... Seem OK so far after all of 30 miles

[EVguru]

You can't use conventional cylinder boring equipment to cut (intentionally) tapered bores, they'd have to be done on a lathe.

The piston crown on a Heron head engine runs quite hot and puts more weight above the gudgeon pin. The original pistons are not a low expansion alloy, so the hot crown means quite a lot of growth in diameter and needs quite a large bore clearance. That along with the (relatively) top heavy design results in a tendency towards piston slap and is often the cause of what sounds quite like tappet clatter once you've got a bit of engine wear. Having the bore tighter towards the top was an attempt to quieten the engine and the gudgeon pin is offset 1mm to keep the piston thrust on one side for the same reason.

In the absence of other information, you always use the bore clearance recommended by the piston manufacturer. I think the Vertex pistons NLM supply are basically OEM spec, but you err on the larger bore clearance because you're not likely to be able to get a tapered bore done. Some rebuilt engines may seem disappointingly noisy as a result.

Forged pistons often need larger clearances than cast due to the alloys used. On the other hand the VW pistons I used for Pete Farrel's 402 conversion are very low expansion and T&L engineering took some convincing to agree to the specified clearance. It was roughly half what they'd normally use on an air-cooled engine.

[Gary D]

Gents

Thank you for your kind assistance. I'll get in touch with Walter Tritshe to see what their recommendations are regarding boring. I like the idea of a bit more poke & renewing 60K pistons, but not at the expense of noise or nipping up?

Cheers for your advice chaps.

Gary

[72degrees]

In the absence of other information, you always use the bore clearance recommended by the piston manufacturer. I think the Vertex pistons NLM supply are basically OEM spec, but you err on the larger bore clearance because you're not likely to be able to get a tapered bore done. Some rebuilt engines may seem disappointingly noisy as a result.

The pistons were still in the boxes with an info sheet so I assume the engineer used their discretion based on what that said compared with the manual, and what I told them the engine was going to be mainly used for (a minute or so of very hard work after warming up as best as is possible with a bike static in a hill climb run queue).

Looking at the PDF available on the Vertex web site this caught my eye!
4 STROKE ENGINES Dirt / ATV / Snow / PWC / Street / Go Kart
50/124cc 125/249cc 250cc & over
[Clearance Data]
"Piston’s usage for 25 hours max 20 hours max 20 hours max."

http://www.na.vertexpistons.com/static/ ... lation.pdf

Looks like a full on MX racing maintenance schedule on a 2T KTM! Or is that just a running in recommendation ?

Also:
NOTE: Additional bore clearance may be necessary for modified engines. (May include head
or cylinder work, aftermarket pipe, or ignition modifications).

Sounds like mine (pun intended)

[EVguru]

Looking at the PDF available on the Vertex web site this caught my eye!
4 STROKE ENGINES Dirt / ATV / Snow / PWC / Street / Go Kart
50/124cc 125/249cc 250cc & over
[Clearance Data]
"Piston’s usage for 25 hours max 20 hours max 20 hours max."

http://www.na.vertexpistons.com/static/ ... lation.pdf

Looks like a full on MX racing maintenance schedule on a 2T KTM! Or is that just a running in recommendation ?

I've noticed before that the data available on the Vertex website seems to all be aftermarket performance oriented.