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Makotosun

Holed piston

  • wayno
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Holed piston was created by wayno

The dt400 I picked up as a project had low compression, pulled the head off and is holed, can the piston size be identified by the stamping 975? My Vernier is at work until next week.
Last edit: 06 Sep 2019 11:26 by wayno. Reason: Missed words
06 Sep 2019 11:25 #1

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Replied by RT325 on topic Holed piston

She'll still be standard, number will be related to clearance on 85mm so bore will measure 85 + wear if any. One things for sure, the compression won't get any lower. Possibly flywheel magnetism you were feeling. Shame to see that & blows all the metal down where ya don't want it. Hope you can clean it out good enough to carry on, but look as closely as you can at the slots in the conrod if a slotted type as little bits get trapped there & if they get into the rollers & make them skid then it's all over. Mains put up with a bit more grief but still not good. Upend it on the handlebars & spray it out, or garden hose in there. I've filled mine with petrol to try & float it out off the top with limited success, then garden hose & spin it over--that's with bike on its wheels. I've got away with it but have seen others come to a halt. Good luck.
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Last edit: 06 Sep 2019 15:16 by RT325.
06 Sep 2019 15:14 #2

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Replied by wayno on topic Holed piston

Thanks for the replies, engine is being stripped anyway for vapour blasting and painting, might as well change everything then. Any recommendations for a piston kit?
06 Sep 2019 23:30 #3

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Replied by liferbiker on topic Holed piston

Thats about the size my IT465 got in Baja years ago! I filled crankcase w/fuel awhile, turned bike upside down, hosed it out (right there in the camp ground!), got a std ( sized anyway) piston from Larry Rossler (race weekend) & I was on my way! litterly, on my way, his 465 piston drastically different, so was my bike, but @ about 5000rpm it gained 30 hp! Worked great, but installed stock w/returned. Raced bike another year then got dealership sponsered Husky 430 @ less than cost. Husky knows how to treat riders even @ dealer level. About a week later I recieved a mountain bike & training videos from them in another crate!
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07 Sep 2019 00:24 #4

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Replied by wayno on topic Holed piston

Tried to get the barrel nuts off today, is there a specific tool? A 13mm spanner through the fins seems to have too much play for my liking, don't want to round them.
Last edit: 07 Sep 2019 09:17 by wayno.
07 Sep 2019 09:16 #5

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Replied by MarkT on topic Holed piston

Socket and extension down through the access holes in the top of the cylinder?
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
07 Sep 2019 10:23 #6

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Replied by MarkT on topic Holed piston

Asking because your description is ambiguous... and an English friend calls what we call a "wrench" a "spanner" and calls what we call a "socket" a "socket".

In any case it's extremely rare to have a 13mm (measured across the flats) nut size on a Yamaha of that era. And the cylinder nuts are special "tall" aluminum nuts. I happened to have a spare cylinder nut on the bench and it's takes a 12mm socket, not 13mm.
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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07 Sep 2019 10:40 #7

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Replied by wayno on topic Holed piston

My sockets wouldn't go down the hole in the head and couldn't get a 12mm "wrench" to locate through the side of the fins, try and get something from work tomorrow.
07 Sep 2019 13:38 #8

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Replied by Blackhat250 on topic Holed piston

Be carefull wayno" they"re as soft as cheeze., a 3/8 drive with deep 12mm will do, , if you round them its a big drill job, , i have pics of the process.
If you aint mixin gas " you aint haulin Ass
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07 Sep 2019 13:43 #9

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Replied by MarkT on topic Holed piston

Six point socket is best if you can find one... Quality 12 point will work... and yes, be careful. They are aluminum... or "aluminium" as you say in the UK.

:Buds
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
07 Sep 2019 17:26 #10

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