offset bush fitting

[5portsrock]

Going to be fitting some offset bushes to a set of s rockers.
. After any advice / do's and donts ?
Thanks alot

[mk1]

Easy.

DON'T!

It is impossible to line the bushes up accurately, meaning that you get a different lift rate on each rocker. I have made a jig to do these in the past but even using that when you check the lift across the set is all over the place.

Much better to use offset forged rockers or best of all modern roller rockers.

If you want to stay "old school" look out for a set of Speedwell 1.5 offset rockers or the 70's Avonbar ones.

[Vegard]

But if you're cheating in FIA-racing, this is the only option Mark

[mk1]

Surely it makes more sense to rebore the rocker & insert a round bush in the moved hole. Much more difficult to spot

[dutchacme]

I appreciate that the lift is all over the place, could you put a number to it ?

How much is to the offset rocker bushes and how much is to tolerances in the other components ? Would swapping rockers around and perhaps carefully adjusting the individual push rod length help make it more even ?

[mk1]

It's impossible to put a figure to it because it depends on how off the bushes are.

Yes matching & careful measuring will help the situation, but it will never totally alleviate the underlying problem.

As a rule of thumb, putting the narrowest part of the bush against the little oil hole in the back of the rocker usually gets them as close to being right as they aver will be & while I think about it these bushes originally came with a set of suitable rocker pillars, do you have these as well as the bushes?.

[Vegard]

while I think about it these bushes originally came with a set of suitable rocker pillars, do you have these as well as the bushes?.

I do
From Longman.

[carbon]

I have set of offset bush rockers, measured valve lift recently and they were all within +/- 0.1mm

[LarryLebel]

I understand the concept of having each cylinder make exactly the same horsepower (i.e. smooth running engine especially at high rpm). But we're dealing with A-series here where I wouldn't think a little variation in the lift would make much difference.

[Ronnie]

I understand the concept of having each cylinder make exactly the same horsepower (i.e. smooth running engine especially at high rpm). But we're dealing with A-series here where I wouldn't think a little variation in the lift would make much difference.

With all due respect if the lift readings are as described + or - 0.10mm that indicates a maximum tolerance of 0.20mm which must equate to about 50% of the tappet settings.

[carbon]

The +/- 0.1 mm is taken from the total valve lift.

Exact readings were 8.12, 8.13, 8.04, 8.08, 7.99, 8.12, 8.00, 8.09

This was valve lift with all of the valves set to 15 thou clearance at the valve.

[5portsrock]

Thanks for all the replies.
Think ill do some before and after measurements and if theres to much variation look at some different rockers. Thanks again

[ianh1968]

With all due respect if the lift readings are as described + or - 0.10mm
that indicates a maximum tolerance of 0.20mm which must equate to about 50% of the tappet settings.

(With even more due respect...)
... this is a totally irrelevant observation as you can set the tappet clearance to whatever you want!

0.2mm is 8 thou, the theoretical valve lift at 1.28 ratio will be 320 thou, so the reality is that
8 thou equates to a 2.5% error.

In the overall scheme of things, "more lift" may well be better, but a 2.5% variation is unlikely
to make the engine perform worse than it did before.

Ian

[Ronnie]

[carbon]

I am pleased to report that the 1293 unit these offset rockers were fitted to went considerably better with these than it did with the previous A+ sintered rockers.