311 piston kit, whats it fit?

[tony27]

Been putting my ty250c back together in time for a 6day trial at the end of the month & have hit a stumbling block, the 1st oversize piston kit I picked up for it a while ago which was advertised as fitting seems to hit the crank
The kit part numbers are 311-11635 00 for the piston
                                     311-11610-10 for the rings

So far I haven't managed to find what these are meant to fit although the piston shows up on CMSNL.com with 438-11635-01 code in brackets which is correct for ty250's.
It looks like the 311 piston is thicker walled & doesn't have the taper at the base of the skirt which some of the 438 pistons seem to have either

Any ideas of what I can do other than fork out another $150+us for a bare 438 piston & hope it arrives in time?

[Davey Crocket]

Just work out how much to trim off the piston to clear the crank, put it in a lathe and cut it down cussy bro. You should be able to get the measurement off the old piston.

[tony27]

If I fit the wrist pin through both pistons at the same time the skirts are the same length, are you saying to make the skirt thinner at the base like the original piston?
Just been talking to the owner/bill payer of the bike & he suggested it may be more enjoyable to use my sherco going on the length of days & ride at my normal harder level rather than use a unproven bike that will need running in at the event, the organisers are saying the loops on the first 3 days will be 20-30kms done twice with start time of 8.30 & expection of at least 6hrs riding each day which could be real fun if it snows again this year

[BETRIC]

HAD LOOK AT SPEED & SPORT, 311 PREFIX IS DT2, IT LIST 438 PISTON FOR THAT MODEL AS WELL

[jimg1au]

zedder for ty250a piston
Part # = 214-11633-00-00
Part Description = PIN,PISTON
Model Count = 56
DT1 1968 250 DT1 Dual Purpose
DT1B 1969 250 DT1 Dual Purpose
DT1C 1970 250 DT1 Dual Purpose
DT1C-MX 1970 250 DT1MX Dual Purpose
DT1E 1971 250 DT1 Dual Purpose
DT1MX 1971 250 DT1MX Dual Purpose
DT1S 1969 250 DT1S Dual Purpose
DT2 1973 250 DT2 Dual Purpose
DT250A 1974 250 DT250 Dual Purpose
DT250B 1975 250 DT250 Dual Purpose
DT250C 1976 250 DT250 Dual Purpose
DT250D 1977 250 DT250 Dual Purpose
DT250E 1978 250 DT250 Dual Purpose
DT250F 1979 250 DT250 Dual Purpose
DT2MX 1972 250 DT2MX Dual Purpose
DT3 1973 250 DT3 Dual Purpose
EF4000DX 2001 4000 EF4000DX 2001    Generator
IT250D 1977 250 IT250 Dual-Purpose
IT250E 1978 250 IT250 Dual-Purpose
IT250F 1979 250 IT250 Dual-Purpose
IT250G 1980 250 IT250 Dual-Purpose
IT250H 1981 250 IT250 Dual-Purpose
IT250J 1982 250 IT250 Dual-Purpose
IT250K 1982 250 IT250 Dual-Purpose
MX250B 1975 250 MX250 Off-Road
MX360A 1974 360 MX360 Off-Road
RT2 1973 360 RT2 Off-Road
RT2MX 1972 360 RT2MX Off-Road
RT3 1973 360 RT3 Off-Road
TX500 1973 500 TX500 Street
TX500A 1974 500 TX500 Street
TY250A 1974 250 TY250 Trials
TY250C 1976 250 TY250 Trials
TY250D 1977 250 TY250 Trials
TY250E 1978 250 TY250 Trials
TY250RD 1992 250 TY250R Trials
XS500B 1975 500 XS500 Street
XS500C 1976 500 XS500 Street
XS500D 1977 500 XS500 Street
YTZ250N 1985 250 YTZ250 TRI-Z ATV
YTZ250S 1986 250 YTZ250 TRI-Z ATV
YZ250A 1974 250 YZ250 Competition Motocross
YZ250B 1975 250 YZ250 Competition Motocross
YZ250C 1976 250 YZ250 Competition Motocross
YZ250D 1977 250 YZ250 Competition Motocross
YZ250E 1978 250 YZ250 Competition Motocross
YZ250G 1980 250 YZ250 Competition Motocross
YZ250H 1981 250 YZ250 Competition Motocross
YZ250J 1982 250 YZ250 Competition Motocross
YZ250K 1983 250 YZ250 Competition Motocross
YZ250L 1984 250 YZ250 Competition Motocross
YZ250N 1985 250 YZ250 Competition Motocross
YZ250S 1986 250 YZ250 Competition Motocross
YZ250T 1987 250 YZ250 Competition Motocross
YZ360A 1974 360 YZ360 Competition Motocross
YZ360B 1975 360 YZ360 Competition Motocross

[firko]

Looking at the Zedder list for Part # = 214-11633-00-00 that Jim posted, the 214-11633-00-00 prefix is for piston port DT1 pistons, nothing else. The TY uses part # 438-11636-00-00. 311-11636-00-00  was superseded by 438-11636-00-00 so they both work for the TY.

[tony27]

Don't know if I'd trust the zedder listing, not 100% sure that the 92 ty wasn't 68mm bore like the other monos
Have done some quick measuring & the original piston measures 66mm on the machined step at the bottom, the 311 measures 64mm but until I confirm that the tapered section at the base of the skirt isn't for clearance on the cases I can't say that the internal size difference is the problem.
Will take a couple of photos of the pistons & post them up before I go to work tonight

[GMC]

Jims zedder listing will be correct, but that listing is for the pin, not the piston.

The piston comes up as…
Part # = 311-11636-00-00
Part Description = PISTON (2ND) - Replacement Number = 438-11636-01-00 *
Model Count = 7
DT2 1973 250 DT2 Dual Purpose
DT250A 1974 250 DT250 Dual Purpose
DT250B 1975 250 DT250 Dual Purpose
DT250C 1976 250 DT250 Dual Purpose
DT3 1973 250 DT3 Dual Purpose
RT2 1973 360 RT2 Off-Road
RT3 1973 360 RT3 Off-Road

Now I have my doubts about this listing as it shows the 250 & 360 pistons as being the same!!!

If I fit the wrist pin through both pistons at the same time the skirts are the same length,

If so then I don't understand how one piston hit's the crank and the other doesn't??

[tony27]

Just tried it back in motor & it's the outside edge by the transfer cutaway that hits the crank, must be the reason for the angle there on the original piston.
Not that keen on modifying it if it's of use to someone else in their DT I have a line on the correct sized ART piston kit which is what the original is rather than the Izumi that this 1 is




Top photo shows the 2 pistons with a wrist pin fitted between them
Second photo shows the angled skirt on the 438 piston
Third photo shows the difference in skirt thickness.

I think that the TY must have a lower barrel with shorter rod than the DT's which would explain the need for the edge of the skirt to be angled

[BETRIC]

Tony27 why do you talk about a 92 TY MONO?? in your above post, I thought you were replacing the piston in a 1976 TY250C (70mm bore) ??

[tony27]

In the zedder listing there was 92ty250rd which is the mono, that's why I was a bit suspect on the fitments although I hadn't realised that the listing was for the pin
Have tracked down the correct ART made piston kit for a ty250c & the 311 kit will be on it's way to Sydney tomorrow
Was surprised at the weight difference between them, ART was 287g, Izumi(311) was 320g

[BETRIC]

I am using a 1M1-##### (77 DT250) piston in my ty250

[firko]

the 311 kit will be on it's way to Sydney tomorrow

Where it'll find a nice new home in my DT2MX motor.

[OverTheHill]

i haven't read all the posts on this but if you want a super strong piston [original yamaha part] the mx250b/yz250c [509] piston/kit just never gives up & was a very strong piston. Hard to find a good pic of one but on 'ebay' there's a piston only on "jgroom888" site that shows a good pic of the piston to see the thickness in the cut away area. Must have a listing number but i'm buggered if i can find it to give you a quick reference, will keep looking for it. Had these type pistons left over from my "75/"76 models & used them them as a stop gap measure in any reed valve DT i've had over the years while waiting for an oversize piston to arrive. [should work the same in a TY250 i'd think]. My Thoughts for the day--Firko---tell me if i'm on the wrong track. Cheers. & Cheers Tony27 [not far away]

[OverTheHill]

found it, ebay item 200857026075.