facebook1   youtube1   twitter1   instagram   linkedin1   pinterest1

logosmallNOTICE:  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!

1971 Yamaha AT1C build thread

25 May 2020 16:41
MarkT
Site Supporter
Site Supporter
Posts: 8088
More
1971 Yamaha AT1C build thread #11
When you say "MX head" do you mean "MX cylinder and MX cylinder head"?

The reason I ask is just using the MX cylinder head on a stock cylinder will give you way too much compression... not a good idea.

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

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

25 May 2020 16:53
JHof44
Novice
Novice
Posts: 34
More
Topic Author
1971 Yamaha AT1C build thread #12
I appreciate the info. I’ll start trying to source an Mx cylinder.

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

26 May 2020 18:27
JHof44
Novice
Novice
Posts: 34
More
Topic Author
1971 Yamaha AT1C build thread #13
Armature came off with no drama thanks to all the tips I’ve read on this site. Time to replace the seals.

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

The following user(s) Liked this Post JayB

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

26 May 2020 18:43
MarkT
Site Supporter
Site Supporter
Posts: 8088
More
1971 Yamaha AT1C build thread #14
Make sure the crank bearing doesn't have play...

Consider using the better IT175 crank seal with proper dual lips to seal pressure and vacuum.

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 JHof44

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

27 May 2020 08:42
JHof44
Novice
Novice
Posts: 34
More
Topic Author
1971 Yamaha AT1C build thread #15
No play in the crank bearing and I did get the oil seal from the IT on order, PN 93103-25125-00.

Now I just need a decent MX cylinder. Found some possible NOS for $400ish, yikes. There's one on ebay with a crack and a bent fin for $300 plus shipping, double ouch.

I'm in no rush though, still have plenty to do. Once I get the bottom end buttoned up I'll move onto the fuel tank. Somebody (my dad) creamed it back around 1991 so I'll need to dedicate some hours to it.

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

28 May 2020 10:03
JHof44
Novice
Novice
Posts: 34
More
Topic Author
1971 Yamaha AT1C build thread #16
I may just end up going with a 175 top end.

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

01 Jun 2020 16:24
JHof44
Novice
Novice
Posts: 34
More
Topic Author
1971 Yamaha AT1C build thread #17
Got it all torn down at this point. I’ll be sending the frame, swingarm, and some other pieces to my brother for sand blast and powdercoat. I will likely start on removing the cream from the fuel tank next, or possibly start rebuilding the suspension and wheels.

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.

01 Jun 2020 19:54
JHof44
Novice
Novice
Posts: 34
More
Topic Author
1971 Yamaha AT1C build thread #18
The free bike just cost me a $500 watch. That’s an expensive learning lesson. Could be worse.

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.

14 Jun 2020 07:35
JHof44
Novice
Novice
Posts: 34
More
Topic Author
1971 Yamaha AT1C build thread #19
I’ve been able to piece together most of my top end. The cylinder head is new old stock but the cylinder needs some work. There’s a surface crack and at least one bent fin so the cylinder will go off to my master fabricator brother to fix that before addressing the bore. I also have a GYT expansion chamber showing up this week.

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

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

26 Jun 2020 08:46
JHof44
Novice
Novice
Posts: 34
More
Topic Author
1971 Yamaha AT1C build thread #20
Unfortunately UPS has lost my GYT expansion chamber. They're "looking for it" but I've heard the same thing for a couple weeks now, so I'll probably start looking for other options soon.This really took the wind out of my sails.

I've been trying to reach Racer's Machine to have the cylinder work done but haven't heard back. Might end up sending that up to my brother's shop too, I don't know at this point.

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

Moderators: yamadminEnduronutMakotosunDEETVinnieDevinJames Hart