facebook1 youtube1 twitter1 instagram linkedin1 pinterest1

NOTICE:  If you are not a free registered member of the site, you will not see the photos in the forum, and you won't be able to access our premium member content. Please consider joining our community! REGISTER AND MAKE THIS BOX DISAPPEAR!

68 DT 250 Crank case ISO threads

  • 68DT250
  • 68DT250's Avatar Topic Author
  • Offline
  • Junior Member
  • Junior Member
  • Posts: 12
  • Likes received: 3

68 DT 250 Crank case ISO threads was created by 68DT250

Revealing some ugly truths about my bikes past as I get into the strip down.
Long and short is my crank case (shifter side) is terminal - cracked !  I have found a replacement (I think) but on the inside face cast into the shell is ISO. My original has no lettering cast on the inside face.
I recall reading about this somewhere on here and know it is the thread type but my question is - what would my original be - and would the ISO marked replacement work?
Any help/advice appreciated.  


21 Sep 2021 05:30 #1

This message has attachments images.
Please log in or register to see it.

Please Log in or Create an account to join the conversation.

  • MarkT
  • MarkT's Avatar
  • Away
  • Site Supporter
  • Site Supporter
  • Posts: 11038
  • Likes received: 6447

Replied by MarkT on topic 68 DT 250 Crank case ISO threads

Hopefully one of the 68 experts will chime in...  I'm pretty sure 68-70 was the same cover going by the parts list.  Later covers might fit but could have had a different finish and Yamaha changed to recessed letters later on.

The ISO marking was something Yamaha seemed kind of proud of...  metric fasteners sometimes varied in size and thread pitch back then, especially the smaller screws...  kind of like sometimes buying something from China these days that has some oddball size fasteners holding it together.  The ISO marking meant the threads were "standardized". 

It doesn't necessarily mean any threads in the pre-ISO marked cover were different...  they probably aren't.
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
The following user(s) Liked this Post: RT325, nhsteve, 68DT250
21 Sep 2021 20:06 #2

Please Log in or Create an account to join the conversation.

  • Posts: 998
  • Likes received: 561

Replied by Swoop56 on topic 68 DT 250 Crank case ISO threads

The only screws fixed into that sidecover would be the oil pump mounting screws ,
and the oil pump cover .
All the case screws only pass through to centre cases , so they will be unchanged .
Looking at my 68 parts list , it appears the oil pump mount screws were isometric ,
so your existing screws should be fine . The two oil pump cover screws were originally
not isometric , so these screws will need replacing with the updated isometric option .
The following user(s) Liked this Post: HouseofEnduro, 68DT250
21 Sep 2021 23:26 #3

Please Log in or Create an account to join the conversation.

  • MarkT
  • MarkT's Avatar
  • Away
  • Site Supporter
  • Site Supporter
  • Posts: 11038
  • Likes received: 6447

Replied by MarkT on topic 68 DT 250 Crank case ISO threads

I found an old Yamaha document... It says the change was to ISO (International Standards Organization) for all threads in mid 1968.  Yamaha sold a new screw assortment to dealers that contained small diameter screws (all under 6mm) and a few 12mm nuts to service the new ISO thread bikes.

My 1964 MG1T has a couple of goofy (and unobtainable) 5mm screws that have an obsolete thread pitch...  the ones I remember are the stator mounting screws that are 5mm x  0.7 pitch and everything these days is 5mm x 0.8 pitch.  I think some of the carb screws are oddball too and different from more modern Mikuni screw threads.

I think oil pump mounting screws are 5mm.  But Swoop says those are shown in the early 68 parts book as ISO so that's great!  It means they won't be the now unobtainable 5mm screws and will be the same as later models...  and you're switching to a later cover which would have the ISO thread pitch that's commonly available anyway.

Oil pump cover screws are 6mm and the pre-ISO 6mm case screws Yamaha used were all 6mm x 1.0 pitch (same as ISO) as far as I know so you shouldn't have any issue at all. 

This image is hidden for guests.
Please log in or register to see it.




 
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
The following user(s) Liked this Post: Swoop56, HouseofEnduro, 68DT250
22 Sep 2021 03:12 #4

Please Log in or Create an account to join the conversation.

  • Posts: 1608
  • Likes received: 1349

Replied by DEET on topic 68 DT 250 Crank case ISO threads

In my experience, if a 1968 Yamaha part does NOT say that it is ISO, any threads in it will NOT be ISO.

My experience is that if a non-ISO case  has 5mm threads in it, they will be 0.90 thread pitch... NOT 0.80 thread pitch.



Just my experience....
This email address is being protected from spambots. You need JavaScript enabled to view it.

Where the Yamaha Enduro is still a current model...
The following user(s) Liked this Post: Enduronut, Rick C., MarkT, swm, 68DT250
Last edit: 22 Sep 2021 10:06 by DEET.
22 Sep 2021 10:05 #5

Please Log in or Create an account to join the conversation.

  • MarkT
  • MarkT's Avatar
  • Away
  • Site Supporter
  • Site Supporter
  • Posts: 11038
  • Likes received: 6447

Replied by MarkT on topic 68 DT 250 Crank case ISO threads

So if the original cover has non-ISO oil pump screws as DEET says it will in his experience...  which makes the parts book Swoop has wrong (which doesn't surprise me about Yamaha literature)...  it really shouldn't be a problem...  in fact it's a benefit. 

If you were swapping to a non-ISO cover those pump screws might be impossible to find.  But since you are swapping to an ISO cover, the pump mount screws will be commonly found...  still available from Yamaha.  Just keep that in mind when swapping over to the ISO cover and don't try to thread your original oil pump screws into the ISO cover if the thread seems different....  buy new screws to fit the new cover.

I suppose the only drawback is if you ever would enter the bike in a concours event and a judge checked the thread pitch of the oil pump screws you might lose points for the threads not being original pitch. 

This image is hidden for guests.
Please log in or register to see it.

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
The following user(s) Liked this Post: Swoop56, 68DT250, Jack
22 Sep 2021 10:27 #6

Please Log in or Create an account to join the conversation.

  • 68DT250
  • 68DT250's Avatar Topic Author
  • Offline
  • Junior Member
  • Junior Member
  • Posts: 12
  • Likes received: 3

Replied by 68DT250 on topic 68 DT 250 Crank case ISO threads

Thanks all for your valuable input. I think I will go ahead with the replacement and (eventually) post some progress.
FOR SALE: Anyone interested in an original cracked crankcase - excellent as a plant pot :)
27 Sep 2021 03:14 #7

Please Log in or Create an account to join the conversation.

  • Posts: 7091
  • Likes received: 2659

Replied by RT325 on topic 68 DT 250 Crank case ISO threads

That brings back memories of the iso change. I worked in the Yam & Honda then & was a pain for a while but soon got used to it. 12 & 13 hex nuts for 8mm bolts instead of 14 nuts if i'm thinking right. & fine threads on screws etc.
27 Sep 2021 03:39 #8

Please Log in or Create an account to join the conversation.

  • Posts: 154
  • Likes received: 165

Replied by Badger52 on topic 68 DT 250 Crank case ISO threads

Here is a unique use of a discarded side case, a light fixture for the Kick Start cafe in PA. Credit to Donzilla’s many creative skills at Metro Racing.
 
288501A
The following user(s) Liked this Post: MarkT, RT325, Swoop56, nhsteve, Sneezles61
27 Sep 2021 06:25 #9

This message has an attachment image.
Please log in or register to see it.

Please Log in or Create an account to join the conversation.

Moderators: yamadminEnduronutMakotosunDEETVinnieDevinJames Hart