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  1. #1
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    Default 1972 t120 bottom and 1975+ top end

    my cases # says its a 1972 but the top is 1975+. i think they tapped the 10th bolt . is this common? im gonna make this my post for this build so if anyone want to take me under there wing i can sure use a mentor for this build. i can and will post pics in the next 24 hrs. please post all u know about this setup . thanx

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    it may have a 1975- later cylinder and head

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    drilling out the 10th hole to use 750 head is not a simple deal, the 9 bolt cylinders need to have that 9th center bolt hole welded up and then the 2 new holes are drilled and tapped but one of them is partially in the welded up hole.
    I've seen it done before but it was on a race motor so the better flowing parallel intake port 750 head could be used.

    But there was a head called the 9 1/2 bolt head used in mid year 1972, it had a cast in 10 bolt boss with no bolt hole that later contained the 10th bolt on the 750 c/c bikes, these heads were often used on bikes that also had 75 m/m BSA pistons, that made it a roughly a 725 c/c engine.

    Pull the head and post a picture of it.
    Last edited by Torch; 07-30-2012 at 10:28 PM.

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    thats what i was trying to say . is that gunna fuck anything up when i get her runnin again?
    is that something commin people do or did? im guessin it was cuz the 750 top was cheaper than the big bore kit

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    cool thanks for the info torch. im gonna get them pic today

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    Quote Originally Posted by bafcms View Post
    thats what i was trying to say . is that gunna fuck anything up when i get her runnin again?
    is that something commin people do or did? im guessin it was cuz the 750 top was cheaper than the big bore kit
    a T140 top end won't work on a T120 bottom end, the difference is the rods, Triumph 750 cylinders and rods are shorter by about 5/16".

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    would u care if i sent u my motor #s and maybe u can help me better understand what im working with?

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    what do u need for pics?

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    so if someone used a diffrent top end off a 750 the the crankarms should be diffrent? also this is a t120rc gh xxxx , is it a five speed ?
    sorry guys i need info help bad !


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    I have a 71 750 top end on a 68 t120 bottom. 9 bolt though. Mine has to be an aftermarket big bore top end of some sort. Maybe that's the case here I don't know. My bike was done by some gear head back in the day and everything from the gearing to the shift pattern is highly tweaked and custom. From the way it runs and the fact I rarely need to brake because of how it downshifts I'm thinking it was a weekend drag bike. Point is you have no idea what you get when you buy these things used

    With the 10 bolt I have no idea. But from what I read and know the cranks are different lengths as was mentioned. And I suppose it can be done but that seems like it would be a huge pain in the ass.

    Torch is one of the only dudes I know on here or JJ that can figure this shit out. Wait for his reply

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    from what im readin lookss like someone put a 750 top on a 650 bottom. i hope someone split the cases and worked the trap i just gotta learn cuz ill die befor i pay someone to do all the work for me.

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    Quote Originally Posted by bafcms View Post
    from what im readin lookss like someone put a 750 top on a 650 bottom. i hope someone split the cases and worked the trap i just gotta learn cuz ill die befor i pay someone to do all the work for me.
    it does look kinda like someone has drilled out the 10th hole on a 72 head, you can see some bolt crush damage from not using the correct 750 center bolt crush plate under the 2 center bolts.


    the easy way to tell if it's a T140 (factory 750) or T120 is to count the cylinder fins...... the 650 cylinders have 8 fins, and the 750 cylinders have 7 fins. (yes, the 650 jugs are taller by one fin)

    Also those engine numbers are strange, the T120R is correct but the "C" is not. it might be a "V", which indicates a 5 speed trans. and the GH indicates June of the 1973 mfg year. look to see if there is little "Triumph" stamps all across the number pads.
    the rumor is because of money and labor problems there were some 650's produced in that period made up from surplus parts.

    Hope that helps, Tony
    Last edited by Torch; 08-22-2012 at 10:20 AM.

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    well im up in new england and i think stamped #s happin a lot cuz of retarted papper work, money, ect... hopfully its not restamped. thanks for all ur help . ill keep u updated on the build .


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