Scratched cylinder -DT1

Succubus · Nov 8, 2005

After I honed the cylinder on my 1969 Yamaha DT1, there remained a scratched in the bore. It is narrow and reaches the length from the port to the top of the cylinder. It will not hone out. It is less than a millimeter wide, but you can see and feel it. I obviously need to have the cylinder bored to a larger size and I need a new piston. O/S pistons for these old Yamaha are as rare as California virgins since there apparently are no other bikes that used the same piston. Yamaha no longer sells them and Wiseco doesn't make one. So, while I search the world for the correct o/s piston (I need one 2nd o/s or larger - that's 70.50mm), what would be the downside to reinstalling the piston and cylinder as they are right now so I can check the integrity of my bottom end rebuild (oil seals, all new case bearings, rebuilt tranny, etc.)? I know I will lose compression through the scratch, but am I liable to cause additional damage to the motor? I don't care about the piston or cylinder because I have a better cylinder that I already was searching for a piston for. Thoughts, anyone?

2stroke · Nov 8, 2005

Well, you could operate on the logic that the bike apparantly ran with that scratch in it before the tear down.

If there are steep, abrupt edges to the scratch Id worry a little bit...could always knock down the edges with some emory cloth.

I guess the concern would be that the piston might explode or seize, but again, if its honed and the piston's been cleaned up as well I dont see that happening.

Ive run jugs with similar defects in them before.

originaldirt · Nov 9, 2005

I have heard of guys with worn iron cylinders that could not find a larger piston use one of the nikasil platers to plate the worn cylinder to the existing piston size. More life out of a worn out dog. Try US Chrome ( www.uschrome.com ) or Langcourt( www.langcourt.com ), see what they say.
OD

SirHilton17 · Nov 9, 2005

I would just leave it if yur on a budget.. like i always am... but if you have got money to burn go ahead fix it

Succubus · Nov 10, 2005

Well, except for that thing about the piston exploding I haven't heard anything that convinces me not to install this cylinder as is. Thanks for the input, guys, I guess I'll see how it goes.. I did happen to locate a guy in Australia who might have the o/s piston I need (isn't the internet wonderful! How did we ever survive without it?), but the price and the shipping are just about equal to the original purchase price of the bike. I mean the price the original owner paid in 1969, not the nominal price I paid when I bought the Yamaha as a derelict cripple a few months back. The piston price is way more than that. Since my money tree died I may have to wait until I can find a more reasonably priced part in the Western Hemisphere.

crazy4nitro · Nov 10, 2005

Look at the pics in my gallery,I have a pic of the gouge that a thrust washer did to my cyl. most of what you see is whatever the washer was made if. Most all of the damage was gone but the indent was there from the trapped piece of washer. maybe a .001" W/ smooth edges. I am currently running this with a new piston/ring., a little comp. loss but nothing to worry about.
the picture is looking down the cyl.

Just my exp.

Crazy

Succubus · Nov 10, 2005

Wow, Crazy. That makes my bore look positively pristine. I'm convinced.....

crazy4nitro · Nov 11, 2005

happy flogging

Master Wrench · Nov 22, 2005

Do not use it as is . It needs to be bored . call Mike at Donnelson's or check out **** . I've seen alot of older DT piston kits there recently .

Scratched cylinder -DT1

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