Triumphrat

jonkster · 11-24-2012, 11:45 PM

Summary: can I use a '72 set of T120 rocker boxes on a '71 and using the '71 head bolts and rocker box bolts?

Details:

I have a 1971 OIF T120 with a non OIF head. (or if it has the right head it definitely has the wrong head bolts).

This is what is on it at the moment:

I am not interested in making a perfect 1971 bike - I just want a reasonably reliable rider. (Having the wrong rocker boxes and long head bolts will make it hard to remove the engine and at the moment the head is also currently leaking so I want to get in here to see what is going on)

I am not sure how they got the motor in there with the older head bolts - I am assuming they jacked and tilted the motor while it was in the frame to insert the long head bolts. I am guessing to get the head off I will need to do the same.

I have sourced a set of 1972 rocker boxes (the ones with the larger opening - I figure that will make adjusting valve clearances easier) and also 4 1971 hex headed head bolts (rather than the round headed 1972 ones) and '71 rocker box bolts.

the 72 boxes and a 71 head bolt and rocker bolt:

Once I get the old bolts out, I am hoping I can simply bolt on the 72 rocker boxes with the 71 head and rocker box bolts.

Is there anything special about the 72 rocker boxes that require 72 bolts? Once I get the old bolts out, should this be a straightforward?

triumpt120rv · 11-25-2012, 08:14 AM

Quote:

Originally Posted by jonkster

Is there anything special about the 72 rocker boxes that require 72 bolts? Once I get the old bolts out, should this be a straightforward?

The 72 round bolts have a 3/8" allen inside to torque your head with the rockers still on. The 71 bolts have a 7/32" allen which is too flexible when torquing (which is why Triumph changed to 3/8" in 1972ish). 72 bolts are preferred.

Ensure that you use the proper thickness washers under the rockers between the rocker cover and the bolts. They are thicker than stock washers and prevent the crushing of the rocker boxes (which may or may not be the cause of your leak. Look for washers # 82-2184 (not 82-1814 as indicated in pic below) You will need 4 of them.

Here is a great pic of 71, 72, and 73 onward bolts from "triumphmike" posted on another site:

Mr.Pete · 11-28-2012, 01:31 AM

There is another stud kit that you can get from Coventry Spares,in the US.
It has 26tpi at the bottom of the stud to suit the 650 barrel.The stud also bottoms out at the bottom of the tapped hole in the barrel (don't tighten down hard),to avoid distorting the head face (a problem with the normal T140 stud setup).
The studs have a 3/8" x 24 tpi thread at the top,to fit the T140 allen head nuts.

If your head is 1971 or later,just use the '72 rocker boxes.If the head is 1970 or earlier,there may not be enough metal around the inner head studs to seal the rockerbox gasket.You could fill the head in that area with JB-Weld,to get enough gasket surface.It only has to seal the gasket,and won't be highly stressed.

jonkster · 11-28-2012, 04:12 AM

Thanks for that fellas.

Mr P, I tried to search for Coventry Spares to see if I could order those bolts but not having much luck. I can get a street address but wondering do they have a web site?

jonkster · 11-30-2012, 05:28 PM

I have been searching for the studs Mr P mentioned without much luck.

Possibly silly question but... suppose I was to take some older head bolts (ie the long pre OIF ones) and cut them and thread one end with 3/8 UNF. I would have some 26TPI CEI to 3/8 UNF studs I could use with T140 top bits.

Any reason this wouldn't work?

triumpt120rv · 11-30-2012, 10:11 PM

While you're waiting for Mr. Pete or others to pipe in about the studs, ponder using 72 bolts if you have them readily available. They will require no modifications and give good service.

P.S. I believe you will have to modify the holes on the 72 rocker boxes to fit the 74 top bits as well.