Big Bore Yamahas

[XFR_Dozer]

I was over to my dads digging though some Tri-z set up notes that i have and I stumbled across some old notes i have on a Tri-z stroker engine. I have been asked by a few people here about bored out Tri-z s performance and ive never been too impressed with the limits of the stock cylinder. Anyhow my notes show a Tri-z case with a YZ k (83) cylinder along with a yz 400 rod. the yz 400 was the predecessor to the 490.i have no specs on the crank though. some gearing notes, suspension setup ,carb and jetting and which pipe i used, but thats about it. I dont ever remember this motor and never raced an "outlaw" engine, but tried some stuff to play with. Have any of you seen a yz stroker motor,or better yet have one yourselves, or have any info on one.

[CHAINSAW]

Ive got a 425 stroker motor Im rebuilding now.. should be done by next time this year. Ill take some pics some time of it, because there has been a lot of time and care put into this monster. Its an 85 Tri Z bottom end. (Cant remember what crank was put in it) Top end was an air cooled YZ400, but fins were cut off, water jackets added and made into a liquid cooled. One-off billet head with interchangable domes, and all the goodies.
The motor last ran in 97, and was on alcohol with a 42mm Lectron carb. With all the heliarching done on the top end, it weakend it all, and broke around one of the base bolts. Ive seen this a lot of big bore motors, and they usually break again soon after, thats why Im not rushing to get it done.
As for any big bores still in existance for the Zs,... I havent seen one come up anyplace I hang out. There might be some of those old motors still around, but highly unlikely.

[XFR_Dozer]

very cool chainsaw . sounds interesting. i was thinking more of just adding the yz 400 rod to a yz engine like in your trike. that would be alot easier than using the Z bottom and the 5 speed should work well with stroker power. you could just shim up the yz cylinder with a spacer but would have to lengthen the power valve rod. im just not sure what kind of crank to use.... im just thinkin out loud . shoot back any more thoughts

[XFR_Dozer]

what is the equation for displacement? im crunching some numbers but have lost my mind somewhere. Btw Chainsaw, after talking to my dad i found that Z motor with the yz 400 con rod. Its my current motor lol. i was a tad confused with my notes. they were for a 82mm yz 465 connecting rod setup. the 400 is seems has a 70 mm rod.my dad was rolling when i asked him if we ever had a motor with a yz400 con rod. he said "didnt you ever notice the spacer under the cylinder?" I had but never gave it much thought. its only a couple mm . ill post some pics of it in a couple weeks when i return up north. i still know nothing about the crank , but in a month or 2 ill find out when it gets torn down and freshened up.

[CHAINSAW]

I dont understand all those equations, and stuff. Like stroke compensating for cc's or anything like that. Im no mechanic (body man mainly,.. thats why machines look nice, but dont run.. haha) and I got this big bore motor along with my dragster that has the YZ motor in it.
If someone could explain it all it would be nice... For example, my big bore is 400cc. By its stroke, its considered a 425cc. So if you could explain that to me I can learn something today.. lol There has been a lot done to this motor that I dont know about. He told me it had cut gears, and I didnt know what those were until a few weeks ago.

[XFR_Dozer]

i assume by cut gears you mean race cut (straight) tranny gears.i gave up on the equation deal and let google do my work for me. here ya go chains . all you ever need to figure out displacment http://www.nightrider.com/biketech/calc_displacement.htm

[CHAINSAW]

yeah, straight cut gears. Glad he did it, because when I found out what it was for, kinda sounds like a waste of time and money more then anything.