mxing my 125-175

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11/10/2016 8:11 AM

have 125 setup ready to put together,but also have 175 setup top end,so what do you think; will this make a torque increase and hp,both fully ported and heads milled. just throwing this up for grabs. this is also going on 125. im 6ft 2 and 217. bike is 1977 yz.

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11/12/2016 2:09 AM
Edited Date/Time: 11/12/2016 2:13 AM

Are you using a barrel from an IT 175 engine? I converted a 1979 YZ125 engine to 175 cc by using an IT barrel. I used a piston from a 1976 YZ175 as it is a single ring piston. The engine went very well but vibrated quite badly.

I found that the IT175 barrel did not match up with the YZ125 engine cases so we had to make up a 5mm thick spacer plate and use a 5mm longer con rod, which may have been part of the reason for the higher vibration. I suggest you measure up both barrels and see if the dimensions are the same at the bottom. I am sure you will find they are different.

I am pretty sure that the later engines (1980 onwards) are a lot easier to interchange.

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11/12/2016 2:14 AM

Here is a pic of my old 125 and the 175 engine is on the ground in front of the bike. Unfortunately I do not have any pics of the engine showing the spacer plate.

Photo

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11/12/2016 9:55 AM

murph- what spacerplate are you talking about,on mine its just a direct cylinder placement 175 on 125 motor, gaskets piston and head an gasket. mike

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11/12/2016 9:57 AM

murph-by the way what year is your 125,nice bike

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11/12/2016 10:08 AM

i am using dt 175 barrell and head havent finished it yet honing and porting work 125 topend is ready to go doing porting on 175 cylinder head needs some milling should be dirrect bolt on if not i will let you know mike ps-using eastwood coatings for ehaust port an pipe more heat coming out and retains more heat in ehaust oort and pipe more horspower!

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11/12/2016 1:58 PM

It is a 1979 yz125. I am pretty sure the DT barrel is basically the same as the IT barrel, but I might be wrong.

When I tried putting the barrel on the YZ cases I found they did not match. The barrel was wider than the cases. We made a 5mm thick spacer plate so that the gap was closed, but this meant using a 5mm longer Conrod as well. I suggest you look at the two barrels and measure them up. I would be surprised if they are the same. If the DT barrel does fit then it must be different to the IT barrel. I would be interested to know.

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