TZ750 cylinder issue

[mavguy]

For my project I got hold of 2 TZ750  cylinders.issue is  cylinder A has a depression above the port while cylinder B has a depression both above and below the port as well holes in the sleeve.does this make it junk or can I still use it(B)?thanks.

[2 Stroke Jamoke]

The port above the main intake port is called a boost port and is supposed to be there on a reeded engine. Those lower cutouts do not look good to me. Especially where it goes all the way through. I dont know much about tx750 but I doubt the lower "port" is supposed to be there

[teazer]

Both of those barrels ahve been modified/screwed up, which is probably why they were available.  I hope they were cheap.

The top (boost) port looks like it has been modified and needs to be squared up. 

The lower port used to improve crankcase filling is way too deep and has broken through at the crankcase mouth, so it's junk as it is is.  It can be welded up and remachined back to stock but that adds to the cost of re-plating.

BTW, what are the casting numbers on the barrels 40900 or 40970 or 40971 or something else?

409 00 are TZ750 a/b and are 64mm bore for a 700cc motor.,  409-70/71 are later 66mm bores for full 750cc motor.

[DesmoDrew]

   Your best bet is to stop looking at them, box them up, and send to https://www.millennium-tech.net  They will fix them.  Luckily everything but the plating is aluminum, so no iron liner to try to work around.  They will do your plating as well.  Just send the pistons you plan on using.   

[Jspooner]

   Your best bet is to stop looking at them, box them up, and send to https://www.millennium-tech.net  They will fix them.  Luckily everything but the plating is aluminum, so no iron liner to try to work around.  They will do your plating as well.  Just send the pistons you plan on using.   

Drew is right, Millennium will fix them, it wont be cheap though. Plating alone is 200.00 a bore which includes minor repairs.

[mavguy]

Cylinder A was actually been replated and sent 

[Jspooner]

cylinder A might be OK as is, cylinder B definitely is not OK.

[Jspooner]

Both of those barrels ahve been modified/screwed up, which is probably why they were available.  I hope they were cheap.

The top (boost) port looks like it has been modified and needs to be squared up. 

The lower port used to improve crankcase filling is way too deep and has broken through at the crankcase mouth, so it's junk as it is is.  It can be welded up and remachined back to stock but that adds to the cost of re-plating.

BTW, what are the casting numbers on the barrels 40900 or 40970 or 40971 or something else?

409 00 are TZ750 a/b and are 64mm bore for a 700cc motor.,  409-70/71 are later 66mm bores for full 750cc motor.

You also need to do as Richard says here and verify if they are for a 700 or a 750.