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  If you thought 775 pistons were big...
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VSDPS
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If you thought 775 pistons were big...
« on: March 9, 2013, 04:04:07 PM »
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This is for a late 70's-80's Bombardier Cam Am 400 MX motorcycle. First over, 84.25mm. I owned a 125, a 175 and a pair of 250's. They were wild; can't imagine what these 400 Rotax singles would be like. Here's one guys experience:

1977 Can Am 370 TNT 

Power
"Where do i start, i bought this thing in a basket and put it back together with a 1 over piston. I fired the bike up with little effort and broke n the motor carefuly. I put the bike in 1st and let out the cluch, the bike dug a 6 inch trench in hard pack for about 10 ft and threw me over high side. That hurt, so i pick myself and decide 2nd would be a better idea. Well i made it about 20 feet before the thing bucked me off again. All this occured with less than half throttle. Once i did finally master not getting thrown off this bike i came to a new understanding of flat scary. Sometimes the bike would instantly take off in a wheelie at insane speed, the whole time doing everything you can to grad the next gear before looping out. Other times you would grab the throttle and the bike would hesitate and then launch off like a bottle rocket. Other times the machine would just run and didnt seem to have any powerband at all. This bike has hurt me several times so i would say it is seriously fast. The only ride that managed to throw me off the back this many times is my Pure bred morgan Horse, and not the steel kind."







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Re:If you thought 775 pistons were big...
« Reply #1 on: March 9, 2013, 06:55:34 PM »
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I'm guessing he's a young man who can take the punishment
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64: Alpine. 66 Olympique. 67 Alpine. 70: 12/3, 335. 71: 292, 775, No-dick 399, Valmont, Auto-ski Torrino 440.  72: 340, 440, 775, No-dick 440. 73: elan 250T.  75 Racoon Elan. 78 Olympique 340. 83 Yamaha Bravo
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Re:If you thought 775 pistons were big...
« Reply #2 on: March 10, 2013, 06:58:38 AM »
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It's easier to add horsepower than to lose weight! 
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Re:If you thought 775 pistons were big...
« Reply #3 on: March 10, 2013, 05:48:51 PM »
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Quote from: webmaster on March 10, 2013, 06:58:38 AM   

It's easier to add horsepower than to lose weight! 


Oh my god, that's the funniest post in ages !
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64: Alpine. 66 Olympique. 67 Alpine. 70: 12/3, 335. 71: 292, 775, No-dick 399, Valmont, Auto-ski Torrino 440.  72: 340, 440, 775, No-dick 440. 73: elan 250T.  75 Racoon Elan. 78 Olympique 340. 83 Yamaha Bravo
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Re:If you thought 775 pistons were big...
« Reply #4 on: March 15, 2013, 03:06:24 PM »
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Two guys in high school used to ride the T'NT 175s, cool bikes and later on a friend had the liquid cooled MX, very fast. The above story reminds me of a guy I know bought a YZ 465, it only took him 10 minutes on it to break his collar bone.
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1965 OLYMPIQUE
1969 12/3 OLYMPIQUE
1969 Ski-doo Tube Trailer scrapped
1970 12/3 OLYMPIQUE with Wunder Wheels kit
1970 Blizzard 640 current restoration project
1971 OLYMPIQUE 335 parted out and scrapped
1972 T'NT 775
1972 T'NT 640 Sold
1972 T'NT 400 Sold
1972 T'NT 340 S
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Re:If you thought 775 pistons were big...
« Reply #5 on: March 17, 2013, 10:24:57 AM »
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I want one of them 400 MX engines to put in a 70 black dot 
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Re:If you thought 775 pistons were big...
« Reply #6 on: March 17, 2013, 11:17:02 AM »
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Quote from: Bones on March 17, 2013, 10:24:57 AM   

I want one of them 400 MX engines to put in a 70 black dot 
Bones


That would be killer especially with the six speed tranny.
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Re:If you thought 775 pistons were big...
« Reply #7 on: March 21, 2013, 05:03:31 AM »
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I've done someresearch about putting a big bore MX engine top end onto a sled bottom end.  I think I have a good plan now but haven't built anything yet.  Modern port design and reed induction with 400+ cc could be fun.  Ah maybe next time the machinists are low on work I'll start them on modding a set of  cases.
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Re:If you thought 775 pistons were big...
« Reply #8 on: April 2, 2013, 05:59:17 AM »
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Just put a ported/piped 277 in it and you'll have more HP than a 400 At least a stock one..

I actually bought a 370 cylinder and head to put on a 277 case. Haven't quite worked out how yet though... The cylinder is pretty huge in every possible way, whereas the crankcase isn't...
Putting it on an older case is going to be very hard I think, the old cases are even narrower than the 277 and even if you could get the transfers to somewhat match the cylinder, there wouldn't be any space left for the clutch I think?
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Re:If you thought 775 pistons were big...
« Reply #9 on: April 2, 2013, 06:06:05 AM »
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Here's what it looks like from below.. If you know that the hole is 84 mm you can get an idea of how wide this thing really is..



The porting looks pretty similar to a 776 and probably other Blizzard engines With the weirdly placed secondary transfers that make it impossible to find usable replacement pistons..
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Re:If you thought 775 pistons were big...
« Reply #10 on: April 3, 2013, 04:40:36 AM »
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Actually was thinking of using yamaha yz400 top end as they share the same 70mm stroke as  a 335/340 single.  Haven't bought any yamaha parts yet though.  I did see oldonelungers new engine in the racing section.
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Re:If you thought 775 pistons were big...
« Reply #11 on: December 29, 2013, 12:32:36 PM »
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I can't resist replying to this old thread, at least it's this year lol. Those Rotax engines used in bikes are just plain bad a$$ ! I used to race Hare Scrambles, in the mid to late '90s I raced an ATK 250LQ, American made pure bread race bike and they use Rotax on them all. There wasn't another bike that could holeshot over it, unless it was an ATK. Even in a few moto cross races I ran, the ATK would get me the holeshot every time. My uncle rode a Honda CR500 and the little 250LQ would give that 500 a run for it's money all day long. ATK also had a 406 and a 605 on their race bikes, they were scary, but OMG what a blast !
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Re:If you thought 775 pistons were big...
« Reply #12 on: December 30, 2013, 06:06:43 AM »
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Quote from: FrankenCub on December 29, 2013, 12:32:36 PM   

I can't resist replying to this old thread, at least it's this year lol. Those Rotax engines used in bikes are just plain bad a$$ ! I used to race Hare Scrambles, in the mid to late '90s I raced an ATK 250LQ, American made pure bread race bike and they use Rotax on them all. There wasn't another bike that could holeshot over it, unless it was an ATK. Even in a few moto cross races I ran, the ATK would get me the holeshot every time. My uncle rode a Honda CR500 and the little 250LQ would give that 500 a run for it's money all day long. ATK also had a 406 and a 605 on their race bikes, they were scary, but OMG what a blast !


Thanks for the info.  I spent some time surfing the net on ATK.  Really cool!
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Re:If you thought 775 pistons were big...
« Reply #13 on: December 30, 2013, 09:47:53 AM »
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Quote from: webmaster on December 30, 2013, 06:06:43 AM   

Thanks for the info.  I spent some time surfing the net on ATK.  Really cool!

There was another race bike that used Rotax engines, may have been TM, it's been a while now. The dealer I raced with sold them both, the TM's were really cool too. ATK was working on an ATV but I don't remember if anything panned out with it. There was an article in one of the ATV magazines, they took a Fourtrax 250R aftermarket moto-x frame and put a Rotax 250 in it, same engine as ATK used. After testing they said the thing is smokin fast and had faster lap times than any other four wheeler they tested in race trim.
Rotax makes great engines ! I don't understand why the race bikes aren't as popular as the Jap brands unless most riders just don't know anything about Rotax. The ATKs and TMs are quite a bit more expensive but by time you actually spend the money to put a Jap bike in race trim it more than evens out.
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Re:If you thought 775 pistons were big...
« Reply #14 on: February 28, 2014, 01:23:42 PM »
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Quote from: 70Oly399 on April  3, 2013, 04:40:36 AM   

Actually was thinking of using yamaha yz400 top end as they share the same 70mm stroke as  a 335/340 single.  Haven't bought any yamaha parts yet though.  I did see oldonelungers new engine in the racing section.


I have tryed to find that "racing section"to read about that engine were is it?

i have one spirit 500 barrel on a 247 it works good with alot of porting and big pwk carb and tund pipe. its fun readig about others crazy sulutions.
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