Head Rebuild

willy mac · Sep 24, 2012

I'm in the process of rebuilding my 750 head and replacing the thackery washers with solid spacers, problem is I can find no definitive measurement for the end float between rocker and spacer.

So far I've found 3 different gaps ranging from 2, 5 and 10 thou, RGM can't find any figure either, has anyone fitted spacers in the past, if so what gap did you use?

DogT · Sep 24, 2012

I would think the reason they used thackery washers was the dimension was variable? But believe me, I'm no expert. I do know that some rockers hit the valve in different places, so the thackery gives one the option to move it with spacers on the other end without producing standard washers. I had to do that with an arm I replaced.

Dave
69S

comnoz · Sep 24, 2012

A couple thousanths is plenty. Not too critical. Jim

Mark · Sep 24, 2012

do they make more noise with larger clearances?

I've been thinking of shimming the rockers on my BSA project in hopes
of making the top end quieter.

comnoz · Sep 24, 2012

I have never noticed a change in the noise. Jim

stockie2 · Sep 25, 2012

I have fitted solid washers on Triumph's and they do quieten down pleasingly. Sometimes the thackery's make click noises and I am pretty sure my Norton is quieter with sold washers, I only gave them a thou or two clearance.
Cheers Richard

pete.v · Sep 25, 2012

I would say this is variable and might depend on how the adjuster is centered over the valve stem.

willy mac · Sep 25, 2012

DogT said:
I would think the reason they used thackery washers was the dimension was variable? But believe me, I'm no expert. I do know that some rockers hit the valve in different places, so the thackery gives one the option to move it with spacers on the other end without producing standard washers. I had to do that with an arm I replaced.

Dave
69S

Hi Dave,
My rockers have suffered the same as everyone else's with the thackery washers wearing a lip into the side face of the rocker, so with that in mind I've done away with them and got a set of bronze spacers from RGM.
Once I've got the info about what gap to use then they won't need done again and with a set of lash caps fitted should be able to ensure that the rocker geometery is as good as it can be.

MFB · Sep 25, 2012

I just rebuilt my head with home-made bronze spacers because I didn't like the notchiness caused by the thackery washers. In addition, 3 of the 4 rockers were hopelessly off centre with the valve stems.
One of them was too far towards the centre of the head, necessitating grinding 2mm from the outer end of the rocker boss. This one required an extra thick spacer as a result.
I was able to centalise the others by just adding an extra thrust washer or two to the outer ends and custom making the spacers as required.
As far as clearance goes, I aimed for zero. Of course I didn't achieve that. As long as it's not tight, I reckon it's ok. Don't forget, the clearance will increase as the head heats up.

Cheers
Martin

willy mac · Sep 25, 2012

MFB said:
I just rebuilt my head with home-made bronze spacers because I didn't like the notchiness caused by the thackery washers. In addition, 3 of the 4 rockers were hopelessly off centre with the valve stems.
One of them was too far towards the centre of the head, necessitating grinding 2mm from the outer end of the rocker boss. This one required an extra thick spacer as a result.
I was able to centalise the others by just adding an extra thrust washer or two to the outer ends and custom making the spacers as required.
As far as clearance goes, I aimed for zero. Of course I didn't achieve that. As long as it's not tight, I reckon it's ok. Don't forget, the clearance will increase as the head heats up.

Cheers
Martin

Hi Martin
Sounds like no two heads are the same, I've managed to get my rockers central on the lash caps by using the original thin thrust washer on the outboard side and then lapping the bronze washer down till it fitted into the inboard side and got the clearance I wanted ( I settled for 5 thou in the end). So the proof is in the pudding! I'll see later on today if it's quietened it down a wee bit??????

Mark · Sep 25, 2012

I posted these pics in another thread.
One of my rocker arms with 39,000 miles on it.

Notice not much of a step worn into it.

I polished up the ends of the shaft and the washers before re-installing.

The rocker is centered on the valve, I never had a problem with it but wanted to see if I could quiet it down a bit.
Cleaning up the thackery washer made no significant difference, but closing up the valve clearance (to 7 thou.) seemed to.

willy mac · Sep 25, 2012

Mark said:
I posted these pics in another thread.
One of my rocker arms with 39,000 miles on it.

Notice not much of a step worn into it.

I polished up the ends of the shaft and the washers before re-installing.

The rocker is centered on the valve, I never had a problem with it but wanted to see if I could quiet it down a bit.
Cleaning up the thackery washer made no significant difference, but closing up the valve clearance (to 7 thou.) seemed to.

I never took any pictures of my rockers but they had lips varying between 5 and 8 thou on each one, now that the spacers are in it does seem a bit quieter, i've set the clearances to standard and will check them tomorrow after the first head re torque.

MFB · Oct 1, 2012

While we're on the subject of head rebuilds, I wonder if anyone else found, like I did, that the oil feed holes to the rockers (the drillings in the head) don't line up very well with the slots in the ends of the spindles? One or two of mine seemed to be restricting the oil passage to a worrying degree.
The problem is that the drillings are made at an angle to meet up with the feed port, but the spindle slots must be "horizontal" to line up with the keeper plates. They can be adjusted a bit , but not much.
To solve this problem, I ground small reliefs in the spindles where they had been covering the holes. I could actually see the "shadows" of the holes on the spindles, which helped to guide my grinding.
When I came to re-fit the spindles, the reliefs also helped to confirm that the spindle was the right way around when it was most of the way in.
Like willy mac said, its seems that no two heads are alike. Maybe I got a "Friday" one.

Cheers
Martin

Torontonian · Oct 1, 2012

Yes Iv'e noticed this. But I thought the oil gallery cutout in the spindle was pointing outwards and opposite the oil supply drilled hole. I'll consult the manual later today as it has been a number of years since I pulled and re-installed rockers and spindle shafts. I thought this was a measure to cut down on oil flow as the head is very over-oiled ? Will check after work.

comnoz · Oct 1, 2012

MFB said:
While we're on the subject of head rebuilds, I wonder if anyone else found, like I did, that the oil feed holes to the rockers (the drillings in the head) don't line up very well with the slots in the ends of the spindles? One or two of mine seemed to be restricting the oil passage to a worrying degree.
The problem is that the drillings are made at an angle to meet up with the feed port, but the spindle slots must be "horizontal" to line up with the keeper plates. They can be adjusted a bit , but not much.
To solve this problem, I ground small reliefs in the spindles where they had been covering the holes. I could actually see the "shadows" of the holes on the spindles, which helped to guide my grinding.
When I came to re-fit the spindles, the reliefs also helped to confirm that the spindle was the right way around when it was most of the way in.
Like willy mac said, its seems that no two heads are alike. Maybe I got a "Friday" one.

Cheers
Martin

If the rocker arm to spindle clearance is reasonable then that will be the point of restriction and very little oil volume will be needed. So if the shafts don't line up well with the hole in the head it makes no difference as long as there is a very small path for the oil to get through. Jim

Torontonian · Oct 1, 2012

Seems correct - according to manual the oil travels through the tiny drilled paths to the spindle end slot ,through the hollow spindle, then enters the spindle cutout oil gallery cut midway, which faces outboard (or away from the head or facing the rocker covers). The idea seems to be to restrict oil flow as the pressure is high.

MFB · Oct 2, 2012

Torontonian said:
Seems correct - according to manual the oil travels through the tiny drilled paths to the spindle end slot ,through the hollow spindle, then enters the spindle cutout oil gallery cut midway, which faces outboard (or away from the head or facing the rocker covers). The idea seems to be to restrict oil flow as the pressure is high.

Yes that's right; the oil has to find its way out by passing along/around the bearing area between the rocker arm and spindle, thus lubricating the surfaces. As Jim pointed out, this is (or should be) the area of greatest restriction. Admittedly my spindles don't show signs of under-lubrication. It's probably just me, I like things to look right, especially when it comes to lubrication.

Cheers
Martin

Torontonian · Oct 2, 2012

Other research says those oil holes should be checked and cleaned out during a head rebuild. Oil should be kept clean. (Duh). The 65 to 66 Atlas motor changed from an oil return line feed to the rocker spindles with the oil gallery facing inwards to a pressurized pump system where the spindles were rotated 180 degrees so that the oil gallerys now faced the rocker covers (to restrict oil flow that was leading to cases of excessive smoking). The spindles were changed to unscrolled to restrict oil flow too and this stayed with the Commando engines.

beng · Oct 2, 2012

I was going through a lot of old rocker spindles recently. There were the old scrolled ones, the later plain ones with a flat machined around the oil hole, and then there was a pair that were plain with only an oil hole drilled with no flat around it.

All these rocker spindles looked really good for used parts except for the set with no flat ground around the oil hole, they showed signs of wear and scoring. Maybe that flat helps hold a useful reserve of oil, or helps distribution? Anyone else have any experience with a set of completely plain rocker spindles vs. ones with a flat ground around the oil hole?

If the clearance between one rocker and it's spindle is greater than the rest it will be a leak and starve the other three, or one which ran tighter than the other three would be starved, seems it is important to have them all very close in dimension.

comnoz · Oct 2, 2012

beng said:
I was going through a lot of old rocker spindles recently. There were the old scrolled ones, the later plain ones with a flat machined around the oil hole, and then there was a pair that were plain with only an oil hole drilled with no flat around it.

All these rocker spindles looked really good for used parts except for the set with no flat ground around the oil hole, they showed signs of wear and scoring. Maybe that flat helps hold a useful reserve of oil, or helps distribution? Anyone else have any experience with a set of completely plain rocker spindles vs. ones with a flat ground around the oil hole?

If the clearance between one rocker and it's spindle is greater than the rest it will be a leak and starve the other three, or one which ran tighter than the other three would be starved, seems it is important to have them all very close in dimension.

All the plain rocker spindles I have seen were scored up. I don't know but I suspect that is why they were only used for a short time. Jim

Head Rebuild

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