Triumphrat

Caulky

Anyone know the diiference between the 70-2620 (650) and 71-3330 (750) pushrods?
I`ve been advised (by GPZ I think) that it would be impossible to fit a 750 tube 71-3329 into a 650 engine. (650 tube 71-2575 *fit 70-9349).
Tube seals are the same.
Strange questions you may think, but it wouldn`t be the first time I`ve found 750 bits fitted to this bike engine.
Just trying to reason why my head is sitting low OR why the valves are opening more than they should...other thread "nasty clicking", pistons hitting exhaust valves.
Originally, I thought: Ah I wonder if the tube seals are different thicknessses. There is a `thin` 650 bottom seal 70-3547...this may make the difference. But I`m pretty sure I didn`t fit these.
But, I`m still using the old pushrods, maybe someone fitted long/er ones, 750 perhaps?

jimmy bush

Don't quote me on this but I think the 750 cylinders were actually a bit shorter than the 650's, at least the one I have in the shed is by about 1/4". I know the push rod tubes are different between a 68 and 69 or 70 onwards as are the tappet guide blocks and head. The 68 tubes are shorter and have a smaller diameter across the bottom hole and a larger diameter across the top flange where the seal rests. That flange wont fit into the later heads without some "modification" and the later tubes wont seal properly on the smaller diameter 68 tappet guide blocks. Ask me how I know.

mark61120

The 650 barrels are 8 fins high and the 750's are 7 (and 6?), so the pushrods are longer.

Ah, the joys of 74 and 75 T120V's and the bottom of the parts bin....

Mark

pookybear

Well,

the 750s are shorter than the 650s.

Pookybear

REG

if pushrod was too long maybe it could cause rocker to hit roof of rockerbox? sure i seen pics here of similar damage or maybe they were of pushrods scoring up the inside of boxes.

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T140E

GrandPaulZ

The gouged backside of the rockerbox internally, is due to incorrectly fitting them up at assembly time. The pushrods will sometimes "feel" like they are properly seated, but are actually contacting the backside of the LIP of the rocker arm, and are NOT seated on the BALL. As soon as they cycle through one or two rotations, they pop off and start cutting into the rockerbox.

I've seen those marks on about 3/4 of all the rockerboxes I've removed, and did it to a few myself 'till I learned the various tips to avoid it, including gaskets with pushrod alignment holes.

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