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TOPIC: DT or MX250 Piston

DT or MX250 Piston 10 Jul 2019 22:17 #1

  • Shane86
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What is the best piston for the 1974 DT250 or MX250? I have noticed the weisco has a different port than OEM. Is this an improvement? I have also heard weisco pistons are harder than OEM and are harder on cylinder walls. I did a search and found some people using some cheap eBay pistons from the UK. Any comments on durability? This is going in a vintage racer.

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DT or MX250 Piston 10 Jul 2019 23:42 #2

  • RT325
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What oversize do you require, do you need to go wiseco as yamaha go up to 1mm or 40 thou over. I like the MX250B piston with the big cut away rather than windows & i'm guessing they all interchange to a point. Depends on ring peg location & gudgeon pin height but i think DT250 & MX are the same. DT cylinder will have smaller porting than MX so ring peg location should be safe. Not sure about the latest Wiseco but the usual older type run about double the yamaha clearance due to different expansion rate & manufacturing process. Consequently they 'can rattle' a bit until warmed up. Had one in my RT2MX cylinder for years but rattle got bad in the end by the time i sold it. Not sure what size this example is but cross references to DT250.
WISECO 1973-1975 YAMAHA MX250 PISTON M07000 234M07000
Auction eBay item number:132284994539

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Last Edit: by RT325.

DT or MX250 Piston 11 Jul 2019 05:42 #3

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Currently it is .25 over. Have not tried to hone the cylinder yet to see if the bore it still good. Interesting point on the clearance. It was bored to weisco spec since the first piston was weisco but dusted that and put a Yamaha piston in. It was low on compression after that. Maybe because of the bore spec Weisco is required. Thanks for the info.

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DT or MX250 Piston 11 Jul 2019 06:12 #4

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Might pay to get the cylinder measured for out of round as honing can make a bad cylinder look good but they wear more around the ports, perhaps not so much on a DT as porting is smaller than an MX where the piston is trying to escape out the bigger ports lol. I wouldn't think the extra clearance in a 'good bore' given to a wiseco piston would make any difference to compression pressure & sealing of the rings if you then dropped a genuine yamaha piston in as only talking a couple of thou extra. Anyway--my thoughts for what it's worth. Cheers.

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Last Edit: by RT325.

DT or MX250 Piston 11 Jul 2019 10:14 #5

  • RacerClam
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Modern wiseco pistons have a high silica content and do not require as much clearence as the old ones did , they expand much less. And Ihave one in my hand right now for a customer whom I am currently doing a porting job for . The recomended clearence is .003 . If your going racing you might consider giving me a call 702-858-9177

Rich
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racerclam

DT or MX250 Piston 11 Jul 2019 10:36 #6

  • MarkT
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You said you used a Yamaha piston in a .25 over bore that originally had a Wiseco piston?

I don't remember Wiseco ever making a .25 over piston. Wiseco sizes go in 0.020" increments which is roughly 0.5 in Yamaha pistons. Using a Yamaha .25 piston in that situation could definitely be the cause of your low compression.

Nothing wrong with Wiseco... or Yamaha pistons.

Enduronut has a huge supply of original pistons and rings in multiple sizes and also can provide boring services to the correct size, if needed. I'd suggest contacting him and sending your cylinder to him. It will be done right and I've always found his prices very reasonable.
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1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

DT or MX250 Piston 11 Jul 2019 13:47 #7

  • Camp3
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FWIW, I was messaging EnduroNut a couple of weeks ago, he said that he has the pistons, rings, and all but has dropped his boring service. Too bad as I have a couple of cylinders that need attention. Maybe it wasn't worth his time or is to busy in the summer. He did a great job on my DT175...maybe something has recently changed as others may know better than me...

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1976 DT175C Now Running!
1975 DT100B Kid Trainer
1974 DT250A 3rd in Que
1992 FJ1200
Primary Home Long Grove, IL
Secondary Home UP of MI

DT or MX250 Piston 14 Jul 2019 05:51 #8

  • Don Dieago
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Im not knocking anyones work but Im sure there is someone in your area that can bore your cylinder and do a great job. any good machinist can do it. Ive had 100's bored over the years with no problems car blocks outboards and bikes.
Some of the best Ive had done was a old man that used a sunnen hone and not a boring bar. but its pain it has to be baby sitted hole time. where a bar can be set to make a small pass and walk away then finish hone for clearance. I think any brand new piston will be fine. I bet you also find your cylinder is egged around ports even though you cant see it

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Last Edit: by Don Dieago.

DT or MX250 Piston 14 Jul 2019 07:02 #9

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Harry's prices are reasonable, he won't mess it up & will chamfer your ports after, so your rings won't hang up.
www.klemmvintage.com/

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1970 DT1-C Grand Prix race bike
1970 DT1-C Street tracker
1968 Honda CL90
1971 Honda Sl 125
1973 Honda CR250
1974 Honda MR-50
1966 Triumph Tiger Cub
1967 Moto Guzzi V700
1970 Suzuki TC90
1947 Mustang

DT or MX250 Piston 14 Jul 2019 07:55 #10

  • mdscott
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Ive used Wiseco pistons for my 74' DT250A and MX250. Though never put 1000's of miles on them.

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Thanks Mark
Roseville, Ca.

'76 Bultaco 143 Frontera
'06 GL1800
07 DL650
74 DT360
75 Norton
73 CB500K
63 C200
87 PW50
64 McClane Edger
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