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73 DT250 piston

13 Nov 2019 11:00
wierzbarecording
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73 DT250 piston #1
I have a 73 dt250 that I am trying to rebuild and source parts. It looks like the oil pump gear cracked, it ran out of oil, then got left outside with and filled with water. Its gross.

I have cleaned it up pretty good, but trying to source a piston. Wiseco says theirs fits 74-79. I called them and got dimensions, and it seems like it should work fine. I just want to make sure, or if I have to adjust squish or anything like that in order to get them to work.

Kyle

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13 Nov 2019 12:14
Gr8uncleal
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73 DT250 piston #2
Welcome from the UK!

Before replying, would you be able to confirm your engine number?

Thanks and regards.

Alan

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13 Nov 2019 13:00
wierzbarecording
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73 DT250 piston #3
dt1f-156183

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13 Nov 2019 13:46
Gr8uncleal
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73 DT250 piston #4
Thanks.

What you have is a 1973 DT3.

The DT250 wasn't introduced until 1974 (with the DT250A) and I originally thought that it had a different engine to the DT3. However, both CMSNL and Partzilla show the two bikes as using the same piston. Just to be sure, I'd wait until one of the other members confirms that the pistons are interchangeable before jumping in!

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13 Nov 2019 14:51
RT325
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73 DT250 piston #5
Motor design totaly changed for "74 & later but run the same bore & stroke & pistons are good to go probably way up to "79, but i'm sure "74 is ok. I've mix & matched all those combo's over the years including yz pistons with the cutaway inlet side skirt. If you run Wiseco [seizco] make sure you follow their clearance recomendations. Modern wiseco's might be quite different but regardlessfollow the clearance which could be double yamaha--like about 3 thou. I've ran one in my 360 with no problems racing it hard out. Was audible piston rattly slightly until warmed up but that's how they are. Regarding the oil pump, just premix it & carry on.

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13 Nov 2019 15:00 13 Nov 2019 15:07 by wierzbarecording. Reason: content
wierzbarecording
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73 DT250 piston #6
Thanks man! Just what I was looking for. Yea, on measurements the guy said 3 thou, my jaw almost dropped. But, that may be a good because there will be some extra wiggle room on the bore.

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13 Nov 2019 16:53
MarkT
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73 DT250 piston #7
Here's a link to the answer to your question coming from one of the foremost experts on Yamaha Enduros and specifically pistons... he probably has an OEM piston and ring set for less than the Wiseco?

Couldn't hurt to check. PM Enduronut through the site or I think his email is This email address is being protected from spambots. You need JavaScript enabled to view it.

Link: yamaha-enduros.com/index.php/forums/1972...tons-in-72-dt2#20411

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

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13 Nov 2019 19:53
RT325
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73 DT250 piston #8
Forgot to ask what oversize your is on or is it still standard 70mm as there must be yamaha original oversizes out there at a reasnable price. I'd tend to only go wiseco if you're out past 1mm over [71mm]. Yamaha go in 10 thou steps [0.25mm steps] so you get shots at it an in an extreme wear case you might need to go two steps to get it to clean up but haven't very often seen that.

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14 Nov 2019 10:23 14 Nov 2019 14:38 by wierzbarecording. Reason: .
wierzbarecording
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73 DT250 piston #9
It is at .5 right now. Piston is stamped .020. Bore seems pretty round. I cant get much of a measurable difference on the bore size in any direction, but its measuring consistently at 70.53mm So I'd stay its still pretty round.

The stamping of the .020 though means that the cylinder was most likely bored for that, and that is larger in theory. So probably going to go with the wiseco on that fact alone to attempt to save me a bore. If it runs a few years, then blows up, I will drop the 200 bucks to do it right later.

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14 Nov 2019 12:52
Swoop56
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73 DT250 piston #10
OEM Yamaha pistons have metric oversize stampings ,
.25 ,.50 ,.75 ,1.00 . Your current piston is likely a Wiseco , as they
stamp oversizes in imperial measurements . Your .20 is twenty
thousandths of an inch oversize , which equates to .50 mm .

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