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1974 DT100A Restoration

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Replied by Scootern29 on topic 1974 DT100A Restoration

If they are not correct, I can make some. I work on shocks and I might have a set that will work.
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03 Jan 2022 11:40 #51

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Replied by Ht1kid on topic 1974 DT100A Restoration

You can reuse the old bushing or they sell them on eBay 

 
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03 Jan 2022 17:20 #52

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Replied by imagelessJAKE on topic 1974 DT100A Restoration

A new problem arises:

when going to remove the flywheel - when grabbing it I noticed a very slight ability to rock it back and forth and up and down.

in my experience bad crank bearings = not a great time

So I went ahead and ordered fresh bearings and seals for the crank/rod assembly. 

Case splitting Fun times ahead!
'68 Yamaha DT1 250
'73 Honda CB350
'74 Yamaha DT100
'86 Yamaha FJ1200
'89 Honda Hawk GT
'17 Yamaha FZ07
05 Jan 2022 11:34 #53

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Replied by imagelessJAKE on topic 1974 DT100A Restoration

Well - the good news is the seller of the shocks was nice enough to include 4x 10mm sleeves with the shocks so it worked with both 10 and 12 - and they came out looking pretty decent despite being ebay shocks.
   
 
'68 Yamaha DT1 250
'73 Honda CB350
'74 Yamaha DT100
'86 Yamaha FJ1200
'89 Honda Hawk GT
'17 Yamaha FZ07
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Last edit: 06 Jan 2022 07:00 by imagelessJAKE.
06 Jan 2022 06:59 #54

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Replied by imagelessJAKE on topic 1974 DT100A Restoration

It gets worse!

So in preparation for bearing and ignition replacement I took the engine out - figured while it was on the bench it might be a good time to inspect piston/cylinder.

First - the reeds looked to be in decent shape so I am not too concerned about them:
  

Then the jug came off and oh man - already spotted an issue - two threads of different sizes on the exhaust studs - looks like ones been replaced. 

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Additionally - found a nice rip in the base gasket for the cylinder (Happy I found that - I already have a gasket for it)

  

Looking at the piston - didnt seem too bad - it has been bored to .25 over until I looked at the side - scratch city!

 
'68 Yamaha DT1 250
'73 Honda CB350
'74 Yamaha DT100
'86 Yamaha FJ1200
'89 Honda Hawk GT
'17 Yamaha FZ07
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Last edit: 11 Jan 2022 11:54 by imagelessJAKE.
11 Jan 2022 11:47 #55

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Replied by imagelessJAKE on topic 1974 DT100A Restoration

Sorry for the awkward pictures - its tough to photograph the cylinder itself. 

So the inside has a significant amount of vertical scratching and pitting as well as some corrosion - measurements put it at around 2.056' or 52.22 mmm 

   
 
 

I am debating with myself what the right way to go is - Boring it out and finding a matching piston - or trying to find a stock jug and matching piston

let me know your thoughts!
'68 Yamaha DT1 250
'73 Honda CB350
'74 Yamaha DT100
'86 Yamaha FJ1200
'89 Honda Hawk GT
'17 Yamaha FZ07
Last edit: 11 Jan 2022 11:53 by imagelessJAKE.
11 Jan 2022 11:52 #56

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Replied by Sneezles61 on topic 1974 DT100A Restoration

Start searching for the jug and top... in the mean time, bore it so you could ride for a while.. Maybe the boring will last you a life time... or maybe it won't... I don't think finding the replacements will be any easier in.. say even 6 months from now... Unless, someone is hoarding a semi load somewhere... Just my thoughts... 
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11 Jan 2022 13:28 #57

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Replied by imagelessJAKE on topic 1974 DT100A Restoration

Thats what I was thinking as well,

Is there any compatibility between model years? for instance some of the early 80's models look like they have the same engine architecture despite having a notch out of the fins.

 
 
'68 Yamaha DT1 250
'73 Honda CB350
'74 Yamaha DT100
'86 Yamaha FJ1200
'89 Honda Hawk GT
'17 Yamaha FZ07
Last edit: 11 Jan 2022 15:20 by imagelessJAKE.
11 Jan 2022 15:20 #58

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Replied by Lizeec on topic 1974 DT100A Restoration

I would slow down a bit, your $500 find is snowballing pretty quickly, the cylinder and the piston do not look to bad from your pictures, have you taken any measurements yet? First step before buying spare cylinders and pistons and all the doom and gloom is to get accurate measurements, looking at your pictures neither the piston or cylinder look very bad, you may be able to run a hone in the cylinder and just a slight piston clean up with a new set of rings. In other words these engines are pretty tough and can take a lot of abuse before needing a complete rebuild. Just my .02¢ if it were my bike, but to each his own.
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Last edit: 11 Jan 2022 19:04 by Lizeec.
11 Jan 2022 19:01 #59

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Replied by imagelessJAKE on topic 1974 DT100A Restoration


Good points, apologies as I dont meant to come across as doom and gloom.. Maybe instead being like pessimistic optimism  

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In the grand scheme this is a pet project - I love the bike and I want to make it the best it can be! Especially if I am going to be riding it daily to and from work - so investing in it is not that big of a bummer to me.

When I ran the cylinder with a bore gauge it gave me 2.056" (Sorry standard gauge set) - and about a thousandths taper

So thats 52.22mm 

have the piston measurements using a micrometer but forgot them at the shop - will update tomorrow.

Agree re: running what we have - after some thought online replacements are not exactly plentiful - so my thought is just to hone - run it and see how it does.






 
'68 Yamaha DT1 250
'73 Honda CB350
'74 Yamaha DT100
'86 Yamaha FJ1200
'89 Honda Hawk GT
'17 Yamaha FZ07
11 Jan 2022 19:31 #60

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