1TuffK0
04-12-2009, 08:00 PM
So, I bought this basket case TRX125 engine, and though I'm still planning to go entirely through it and freshen her back up. I am however, second guessing any choice to put it in my ATC70 with it being a 1973 model. So I'm wondering just how big I could go with the 70 based engine so I could maintian a more OE appearance. I've looked around dratv, etc and if I'm understanding correctly I could actually take things up to something around 120cc. Is that correct????
I was told a while back to do something along the lines of starting with like either an 85 lower end or just the cases because there are bearings somewhere that aren't there on the earlier ones, for lower friction. Perhaps crank bearings, don't remember the specific advise. Then, if I remember right I should perhaps use the trans gears from an XL70, etc., and even use the top end. Was advised that the XL/SL trans gears were a better ratio, and that the top end is a big valve head. Oh, and almost forgot the important part, I could use the manual clutch parts from the XL/SL as well .
So, curious what options I have for a 70 build. Would love to use the best of the best OE parts, or aftermarket but OE appearing. Which ever cases are the best, whichever trans gears would give perhaps a real low first, but tall fourth gear for some speed capability to. Wish there was the hi/low option on the 70, but oh well. Then, would love to know the best head to use. I am equiped to do basic port matching, and or blending/porting (no flow bench though). Then, I'd try to pick a cam with mild duration for good low end response, but the most lift to take advantage of any port flow improvements I can possibly make, as well as helping a bigger cc engine breath. Not sure of carb to use, perhaps just use the TRX125 carb I have.
I assume if I stay with a 70 based engine, that it would also allow me to still use the stock left crank case cover so I could use the unique to 73/74 side attached bottom skid plate.
Any input on my 70 based engine build options would sure be appreciated, as I'm definetly unclear on the best options of each part, etc.
I was told a while back to do something along the lines of starting with like either an 85 lower end or just the cases because there are bearings somewhere that aren't there on the earlier ones, for lower friction. Perhaps crank bearings, don't remember the specific advise. Then, if I remember right I should perhaps use the trans gears from an XL70, etc., and even use the top end. Was advised that the XL/SL trans gears were a better ratio, and that the top end is a big valve head. Oh, and almost forgot the important part, I could use the manual clutch parts from the XL/SL as well .
So, curious what options I have for a 70 build. Would love to use the best of the best OE parts, or aftermarket but OE appearing. Which ever cases are the best, whichever trans gears would give perhaps a real low first, but tall fourth gear for some speed capability to. Wish there was the hi/low option on the 70, but oh well. Then, would love to know the best head to use. I am equiped to do basic port matching, and or blending/porting (no flow bench though). Then, I'd try to pick a cam with mild duration for good low end response, but the most lift to take advantage of any port flow improvements I can possibly make, as well as helping a bigger cc engine breath. Not sure of carb to use, perhaps just use the TRX125 carb I have.
I assume if I stay with a 70 based engine, that it would also allow me to still use the stock left crank case cover so I could use the unique to 73/74 side attached bottom skid plate.
Any input on my 70 based engine build options would sure be appreciated, as I'm definetly unclear on the best options of each part, etc.