Biggest ATC 90 motor ever 275cc WOW

[shortline10]

Was asked by someone about putting a honda 175 head on an atc90 bottom end so here ya go . This is real trick and done a long time ago back in the Fall of 1980 .

[3wheeledjunkie]

Holy big jug batman! How do you explain the gigantic head/cylinder and mean ass sound when you pull up to race a little kid on his stock 70. "OH this nothing much just been bored and baffles out of the muffler."

[atctim]

WOW - just plain wow. Talk about a big bore kit. 3 times the OEM displacement. Imagine doing this to a 350X!!!! - ATC1050X - LOL - I know it isn't really possible - just saying. Wonder what kind of HP that motor put out. I bet that little critter would haul the trash to the curb!

[Pafrig]

1000+ cc's would be possible with two cylnders.... Harley conversion anyone??? Haha atc 1600x. It's so rediculous that it might just work...

[harryredtrike]

use the inline fours from honda,its been done and wow its alot of motor.

[Vealmonkey]

Why must you show me these things! I'm getting my shopping list together now!

[big specht]

Damn how do you blow that up so you can read it ?????

[atcrider1]

do you have any of these hiding in your shop?????

[greenhuman]

Been there done that only mine and the other ten I made were 310cc with the possibility of 360cc.

I actually went to Helm and Son with pictures of mine in 1982 and they were shocked. The head machinist said they never got theirs running and couldn't believe there were heaps of them running in Australia. Theirs was just a story for the magazine.
Mine used a highly modified Honda XL125 crankshaft stroked to 67mm and a 76.5mm Kawasaki big bore piston kit. The 90/110cc strokers would not have been big enough to run an XL175 top end. Thats why the XL125 crank was used. Larger diameter and width. The main bearing were surface ground 1mm per side so even more width could be retained on the crank which was also balanced. The oil pump drive shaft was made from stainless steel and was 3mm in diameter so the crank could be made larger. An XL175 larger pitch cam chain was used also.
The pull starter had stainless steel cable and starting them was an art. I remember one day I left mine idling in my backyard while I went in the house to get something and when I came out the trike had bounced about 20 feet across the yard and was hard up against the fence. The torqueist thing I ever owned.
I still have some cases and a crankshaft.

[userj8670]

thats facking nuts!! WOW! But what would have to be done to do this to the 350x? I would be very interested in trying that if anyone has any ideas.



*edit* I was thinking....Technically someone could do this to a 250sx. Put a 350x jug and head on a 250sx correct??????? If thats the case im going to really get cooking with this...

[Micahdogg]

green human, did you run into as many timing chain issues as Helm did? That definitely looked like the nastiest aspect to it.

[rdlsz24]

Damn how do you blow that up so you can read it ?????

Click the image above and it will open in a new window. In that window click the image again and it will zoom

Rob

[greenhuman]

green human, did you run into as many timing chain issues as Helm did? That definitely looked like the nastiest aspect to it.

Because my crankshaft was custom made, I had the flywheel side made longer so the bottom timing sprocket was more toward the outside which help line up the bottom with the top. The cam still had to have a couple of mm machined off the sprocket face. I was then able to make a 3mm spacer plate for the stator case which made that case miss the cam chain.
A lot of thought went into this motor. Thats probably why I can still remember all this nearly 30 years later!

[Yamada]

Because my crankshaft was custom made, I had the flywheel side made longer so the bottom timing sprocket was more toward the outside which help line up the bottom with the top. The cam still had to have a couple of mm machined off the sprocket face. I was then able to make a 3mm spacer plate for the stator case which made that case miss the cam chain.
A lot of thought went into this motor. Thats probably why I can still remember all this nearly 30 years later!

But how fast was it? Say compared to a 350X?

[oscarmayer]

fyi, i jsut left a message for Lee Helm to conact me when he gets in next Wed. to discuss somedetails. I'm going ot see if he has any kits left in the back or can provide me with the specs so i can have a replica made of their engine. While they used welded 90 rods, I'll have 2 custom made so they are more exact.

I'll keep you guys posted.,

FYI this will be going onto my son's kiddy ATV since he;s been wanting more pwoer, Eh, Why not?