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Discussion Starter · #1 ·
Hey guys I scored this "race" engine recently. The engine is a 71 T120R. This weekend I split the cases and found a few things that I'm questioning and need some help.

First off is there a way to identify the crank is stock, modified stock or something else? Doesnt look stock to me.



Then the cases look modified. It looks like there has been alot of grinding done. The small flat head screws that bolt the cases together by the cams are missing along with the holes. Also there is no breather tube by the sprocket or hole in the intake cam bushing area.







Thanks
 

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It looks like there was some material removed from the throw probably for balancing (the way the top of the throw looks, I have seen 750 Honda cranks that were welded up and off set ground to stroke it look the same, so possibly you would have to measure the stroke of one to be sure, but i'm just guessing).

The cases dont look to be anything special, (the way they are ground some under the cam bushings could also be to clear a little additional stroke, see above but again just a guess) the holes where they bolt together are kind of odd and late cases dont have the hole for the breather out the intake cam, they breathed through the primary (their should be a bolt on "bung" on top of the motor above countershaft sprocket)

Any pics of the pistons out of it? what about cams?
 

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CJ, it looks like it could be stroked, Without actually measuring the stroke(the obvious best way to know),you could also look for the "other" signs of a "stroker",a plate under the barrels, pistons with modified pin location, modified rods,etc. lay out all the parts and compare with stock. Jack
 

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...looks like a stock one but balanced and with the flywheels polished
the grinded part is to manage better the "flow"
the screw and hole you say, possibly is like mine, that s a ´79, so have those screws outside the cases..I cannot see that in your pictures
 

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Lindy is correct, those are standard 1970 and later 650 cases, you can see the three 1/16" breather holes to the rear of the primary main bearing in pic. #2.

Eric
 

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it all looks stock to me, if you have any problems/questions bring it by the shop. we are in Orange to.
 

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Although certainly there are mods to the crank that can provide more horsepower, most of your Triumph hop up tricks are in the head and choice of displacement. Check your cams for "H&C" stamps or a yellow color to them. Check to see if your camshafts have been relobed. Measure lift and duration if so. Compare a stock head to your head with special attention to the intake track to see if it has been ported. Look for drilled and lightened cam wheels too.
 

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The crankcases might have had a norton atlas/commando crankshaft in them at some stage , if you do this you have to grind away metal in the cam bearing areas for clearance for the big end of the con rods as the norton crank has a longer stroke (89mm as opposed to 82mm). The norton crank + 750 cylinders gives 830cc.
 

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Looks like a stock crank that has been balanced. Probably not a stroker, but if you want to check, just put the crank in the cases, put a piston on one rod (no rings) and put the cylinder on, then measure the up/down distance and compare with the manual.

Grinding beneath cams is probably for extra clearance because those cranks swing around in there quite a bit at high rpm.
 

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Discussion Starter · #11 ·
Thanks Guys,

This is my first Triumph rebuild but not my first motorcycle build. I dont have any stock parts to compare too. I only have Wes' DVD, the internet, and a Haynes manual to compare.

Heres how the engine looked when I got it.



The head looks stock. Heres the intake port.





The cam gears dont look stock to me. They are thinner then the new set I got off ebay. The timing cover was missing thats why the gear is so rusty.





The rods look stock to me.





I did find this in the cam idler gear shaft hole. I got this engine for free so Im not attached to it and can dump the cases if needed. I can tig weld and my friend is a machinist Im just not sure I can get deep enough in the hole to fix it. What do you guys think? Save the good parts and toss the cases or fix them?

 

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I did find this in the cam idler gear shaft hole. I got this engine for free so Im not attached to it and can dump the cases if needed. I can tig weld and my friend is a machinist Im just not sure I can get deep enough in the hole to fix it. What do you guys think? Save the good parts and toss the cases or fix them?

A pretty tough fix without a fixture or jig to get it located again. my opinion a better option is to pick up a set of good cases, or if the primary side is good, you will be surprised by how cheap new crankcase halves are, line ream them and you are set.
 
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