ESE's works engine tuner

**Frits Overmars** · 15th October 2015, 11:44

Originally Posted by peewee

..my plan was to weld the dam on all sides, preventing any oil or fuel from entering the airgap..

If you weld the dam on all sides so the air gap below it is completely sealed off, then why not take the opportunity and turn that air gap into a coolant volume?
It would be great to have a raised exhaust duct floor from say 3mm sheet material with water flowing underneath.

**2005bully** · 15th October 2015, 13:07

Without luck I have been trying to find the proper forum to ask the following question...

Older YZ250 pistons are commonly used in the Current YZ250s as big bore pistons. Depending on the model the wrist pin height is 2mm to 5mm lower..(which is not a problem for my this aplication) Are there certain models to avoid because of ring pin location, ex bridge holes, miss matched ex skirts, etc etc?????.
Can somebody suggest the proper forum to ask this question?
Thanks Kermit Buller

**peewee** · 15th October 2015, 13:16

thnx for the tips frits. i didnt think about having water go through the underside of the dam but it would be easy enough to do. water flows around the exh port now so all i would have to do is make two holes through the floor so the water can pass in and out from underneath.

**peewee** · 15th October 2015, 13:21

Originally Posted by 2005bully

Without luck I have been trying to find the proper forum to ask the following question...

Older YZ250 pistons are commonly used in the Current YZ250s as big bore pistons. Depending on the model the wrist pin height is 2mm to 5mm lower..(which is not a problem for my this aplication) Are there certain models to avoid because of ring pin location, ex bridge holes, miss matched ex skirts, etc etc?????.
Can somebody suggest the proper forum to ask this question?
Thanks Kermit Buller

if your wanting a standard sized 250 piston with pegs directly in the rear then check out the ktm250. im not sure if any of the other 250 engines used 6' 0clock pegs . you can look at pictures on ebay and get a idea what each piston looks like. you can always have the pegs relocated also

**husaberg** · 15th October 2015, 13:39

Originally Posted by 2005bully

Without luck I have been trying to find the proper forum to ask the following question...

Older YZ250 pistons are commonly used in the Current YZ250s as big bore pistons. Depending on the model the wrist pin height is 2mm to 5mm lower..(which is not a problem for my this aplication) Are there certain models to avoid because of ring pin location, ex bridge holes, miss matched ex skirts, etc etc?????.
Can somebody suggest the proper forum to ask this question?
Thanks Kermit Buller

**2T Institute** · 15th October 2015, 15:10

Originally Posted by F5 Dave

Yeah we've only 100cc, 125s have carb restrictions.
Never found that bearing to be a problem. Maybe you had case alignment issues?

Everyone had a issue with that bearing, think it was the bearing itself as the rivets/cage would disintergrate with hindsight(and nearly 20yrs of learning) a polymide cage would probably fix that. The finning on the cylinder could never get rid of the heat though, but beat the four strokes until they were allowed 200cc

**MotleyCrue** · 15th October 2015, 16:55

Originally Posted by peewee

you can always have the pegs relocated also

This is something I am looking at having done on a different engine and have no experience with it. Are there any tricks to it, how much of a press fit is needed etc. etc. ?

**peewee** · 15th October 2015, 17:41

it may depend on the type of piston used and material of the peg. wiseco told me their pegs are around .003" interference fit if i recall. i think they just use a standard carbon steel.

**F5 Dave** · 15th October 2015, 18:58

Originally Posted by 2T Institute

Everyone had a issue with that bearing, think it was the bearing itself as the rivets/cage would disintergrate with hindsight(and nearly 20yrs of learning) a polymide cage would probably fix that. The finning on the cylinder could never get rid of the heat though, but beat the four strokes until they were allowed 200cc

The old Double the size trick huh? That'll make it nice and unfair.

Was thinking about the MX application of the Ryger, there could be a market to be tapped right there. Get in bed with TM and KTM and watch watch what happens next. Clearly protests, but they are still legal and if emissions reduce then it is harder to argue against them. Maybe. But you wouldn't want to wait too long.

**karter444** · 15th October 2015, 19:36

Originally Posted by Frits Overmars

If you weld the dam on all sides so the air gap below it is completely sealed off, then why not take the opportunity and turn that air gap into a coolant volume?
It would be great to have a raised exhaust duct floor from say 3mm sheet material with water flowing underneath.

with water flowing underneath.

to follow on from peewee,s post and ask a few questions that may help both of us with our exhaust post modifications . maybe Frits and Wobbly could comment and head us in the right direction .
My idea was to weld a vertical plate just inside the ex port entry up to a height just below tpo then weld from the base of the plate gradually raising the height of the ex port duct floor to achieve the exhaust duct exit shape as recommended by Wobbly . The reason for the vertical plate was to eliminate a heap of welding they may cause some barrel distortion , also its difficult to get into such a confirmed space to weld
I don't think that the bottom half of the port does much apart from allowing a big radius that gently pushes the ring back in , but the vertical plate may effect the returning mixture by forcing it upwards towards the cyl head as it enters the cyl and may effect the way the pipe works on the transfers , it could possibly be a help , that's something I don't know
If you think that the vertical plate is not a bad idea , would there be a better way to do the transfer ports . as the ports are commonly angled upwards and away from the exhaust to minimise the mixing of the incoming fuel with exhaust and reducing the incoming fuel to enter the exhaust port and as the vertical plate may eliminate this problem there may be some power gains by changing transfer port angles
cheers .

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**Frits Overmars** · 16th October 2015, 00:13

Originally Posted by peewee

if your wanting a standard sized 250 piston with pegs directly in the rear then check out the ktm250. im not sure if any of the other 250 engines used 6' 0clock pegs

First time I've seen this 6' Oclock indication for the ring peg position. But it's perfectly logical; I love it and I 'd like to adopt it.
Now I'm just wondering about the correct spelling: 6 Oclock , 6-Oclock , 6 O'clock , any more variations?