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ISO 25mm crank pin halves / 1973 DT3 250
- tzsv4k
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ISO 25mm crank pin halves / 1973 DT3 250 was created by tzsv4k
I am in search of NOS or good used crank halves for a 1973 DT3 250 with 25mm crank pin. One of my bikes has a 25mm and the other has a 24mm. I mis measured while the cranks were still a single unit and purchased the Vintco rod kits for these bikes. I'd like to keep all the same replacement parts the same. If anyone has a line on said parts I'd appreciate it. The Yamaha part numbers are all over the place so I don't know the exact number but this is close. 214-11412-02-00, 214-11422-01-00, 214-11422-00-00. Thanks. Ron
Twin 73' DT3 250's, 73' MX 360, 83' TT600 , 73' MX 100
05 May 2022 14:20
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- RT325
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Replied by RT325 on topic ISO 25mm crank pin halves / 1973 DT3 250
Hope i don't confuse things but i think 25mm is a 360 pin. Same rod but smaller rollers. But i have a YZ250A crank with uses a 25mm pin too--but yes normal 250 is 24mm. Stroke difference is easy to see as on a 250 the pin breaks in to the bit where the main bearing butts up to the crank. 360 pin sits just out from that piece. I run a 360 crank in one of mine--just because--280cc.
The following user(s) Liked this Post: MarkT
05 May 2022 18:57
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Replied by tzsv4k on topic ISO 25mm crank pin halves / 1973 DT3 250
RT325 I don't think you can confuse things any more than Yamaha has in their parts numbering system. You may be correct. I've always been asked which crank I have when asking for NOS parts. It's crazy Yamaha throws multiple models into one schematic diagram when unique part numbers exist. Thanks for your reply.
Twin 73' DT3 250's, 73' MX 360, 83' TT600 , 73' MX 100
06 May 2022 10:14
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- MarkT
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Replied by MarkT on topic ISO 25mm crank pin halves / 1973 DT3 250
The original Yamaha parts sheets/fiche were actually pretty AWESOME. You could see which parts fit what and what interchanged between 250/360 for example.
It's the modern "digitizing" of the original parts books that screwed everything up. The columns were lost that ID'd what part fit what.
It's the modern "digitizing" of the original parts books that screwed everything up. The columns were lost that ID'd what part fit what.
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
06 May 2022 12:04
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- tzsv4k
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Replied by tzsv4k on topic ISO 25mm crank pin halves / 1973 DT3 250
MarkT...interesting ... never knew why it looks so confusing. I'm a numbers guy and I'll be dang'ed if I can't figure their system out.
RT325...are you saying the '250' crank and the '360' crank have different stroke lengths? I pulled the 2 different cranks out of 2 identical DT3 engines. Think the 2 cranks create different squish clearances?
I'd like to mock up the top end build without installing the main bearings to check squish and fitment. Can you think of any way to do this allowing for a 'slip' fit assembly rather than a 'press' fit assembly? Main bearings don't come in close enough increment sizes to buy different bearings. I can only think of machining a piece that allows for a slip fit on the crank and case surfaces. Like .5 mm over and .5 mm under to allow for slip fit. Or using the old bearing and 'milling' the fitments to allow for a slip fit. But bearings are too hard to just 'sand' them down.
Thanks guys.
RT325...are you saying the '250' crank and the '360' crank have different stroke lengths? I pulled the 2 different cranks out of 2 identical DT3 engines. Think the 2 cranks create different squish clearances?
I'd like to mock up the top end build without installing the main bearings to check squish and fitment. Can you think of any way to do this allowing for a 'slip' fit assembly rather than a 'press' fit assembly? Main bearings don't come in close enough increment sizes to buy different bearings. I can only think of machining a piece that allows for a slip fit on the crank and case surfaces. Like .5 mm over and .5 mm under to allow for slip fit. Or using the old bearing and 'milling' the fitments to allow for a slip fit. But bearings are too hard to just 'sand' them down.
Thanks guys.
Twin 73' DT3 250's, 73' MX 360, 83' TT600 , 73' MX 100
28 May 2022 13:05
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Replied by RT325 on topic ISO 25mm crank pin halves / 1973 DT3 250
Hmm, whatever i said was likely confusing lol but you can't mistake a 250 crank or a 360 crank as the 360 has a 70mm stroke where the 250 only has 64mm stroke. Cranks look the same until you look close at pin location. If you have all 250's they should all be the same. 360 crank would have the piston out the top of the cylinder by a few mm. Not sure [but don't think] 250 trail models ever went to the bigger pin, but i have a yz250a crank that i'm sure is a bigger pin although that doesn't change the stroke in any way & is only running a bigger pin but smaller diameter rollers into the same conrod eye size. Yep confusing. Not sure you need to do dummy runs with the crank to set the squish. Just bolt it together then play with base gasket or head gasket or machine the head as needed. If you 'did' want to pull the crank easily to experiment then the right side bearing 'should' just slide on. Left is super tight. So i'd spin emery cloth on a rod in the drill & ease the old bearing [won't take much]. & same with the right side bearing which will take even less easing. If ya talking bearing outside diameter to fall in & out of the case for practice, i'd find a way of spinning it locked up in the lathe & sand the outside until it 'just' falls in. Talking increments of bearing size--that only refers to the internal fit of the balls --like std then c3 & c4. Extra clearance [ball clearance] is normally to allow for being tight in the case plus tight on the shaft--so squashed from outside & expanded from inside. Sorry--essay time. Some of it might even be correct lol.
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- tzsv4k
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Replied by tzsv4k on topic ISO 25mm crank pin halves / 1973 DT3 250
Both cranks are from a DT3 engine. When the machine shop called and said on pin is a 24 mm and one pin is a 25 mm, we had to 'scramble' because I got Vintco rod kits that fit a 25 mm pin. So I'm assuming Yamaha went from a 24 mm to a 25 mm at some point in the 250 cc engine designs.
That is a great idea...spinning emery paper on the ID and spinning the locked bearing on a disc.
It would be easier to manipulate squish with it apart I feel.
And I was able to follow everything...
Thanks.
That is a great idea...spinning emery paper on the ID and spinning the locked bearing on a disc.
It would be easier to manipulate squish with it apart I feel.
And I was able to follow everything...
Thanks.
Twin 73' DT3 250's, 73' MX 360, 83' TT600 , 73' MX 100
The following user(s) Liked this Post: RT325
29 May 2022 22:35
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