Thread: Brake hone

Line boring is to get the bushes to the correct size and in a straight line so that the rocker shaft fits in with a minimum clearance.
If you hone (reaming would be a much better option) you may have to make some bushes oversize so that the rocker shaft fits through.

An adjustable reamer with an extra long pilot shaft might do but line-boring would be best unless someone knows better.


Colin

I've done master cylinders before - but with a 3-stone hone.
Honing isn't meant to remove significant material, and unless you can mount it in a way that the driving end of the hone stays central you will end up with the ends of the bushes flared out if you spend a while removing material.

I'm not familiar with the motor, so I'm assuming that you've got a head with some bushes in it, the rocker shaft goes through those and you're trying to get them the right size for the shaft and in line.

If the holes that the bushes fit into are in line (ie line bored originally), then maybe an option is to get them measured, and then bore the internal diameter of the bushes close to the correct size before fitment (allowing for the reduction in size due to the interference fit). A decent machinist should be able to get them pretty close. Then you're only having to remove a smaller amount after fitment to get them to the required size (rather than trying to remove a larger amount of material with a hone).

Steve

Is this what you're talking about?

90512208 VALVE ROCKER EXHAUST | shop | www.lrseries.com | L. R. Series

Then they should be reamed or line bored as honing won't be accurate enough and they'll rock sideways, which they're not supposed to. Also, if I remember it right, oil goes through the rocker shaft and if the arms aren't an accurate fit on the shaft then too much oil will leak out the sides of the bushes.

Are you asking because you put new bushes into old rocker arms?

Also, I haven't heard of anyone honing disc brake parts. Do you mean the bores in the calipers where the pistons go?

I have given caliper bores a quick hit with a bottle brush hone to remove surface corrosion but thats about it

Steve, Davo, Dave,
Thanks for your advice/comments.
Davo's link shows the parts I need to ream/bore. What happened is the original shaft had a step of a millimetre through the hard casing in one place, and two other of the valve rockers had slop from worn bushes.
I have bought a supposedly NOS rocker shaft and bushes from Paddocks, the bushes have been pressed in to line up with the oil feed gallery. The bushes are brass with a coating of whitemetal, and have a split to allow them to 'crush' into the valve rocker.
I looked at adjustable reamers, but was warned off as they are apparently eager to bite where the split is and leave it out of concentric. I hoped something less aggressive, such as a hone, would keep it concentric.
Because the rockers are an odd shape, and there are both left and right handed offsets, the machine shop that had them for a few months suggested they could make up two tools to hold the rockers in place whilst they bored them, but since it is fairly deep and narrow, they couldn't guarantee the boring bar would not deflect, leaving the bush cone shaped.

I'm open to any advice, as this one problem has held up rego since August last year.

I'll keep shopping around for someone that can do the job properly I guess. I don't really want to pay $800 for this, when a running replacement engine costs far less.

Turner Engineering - Remanufacturer of Land Rover Engines and supplier of Land Rover engine parts

I would just phone up these guys and see if they can help. They're a good mob and always helpful even when I've just asked for a quote or information about something. (Though I have bought things too!) They may be able to supply rockers reamed and ready to go, or at least tell you how they machine them.

Anyway, welcome to the world of engine work! It always seems to be complicated and expensive to get the job done right, though in the end it's usually worth it to get it done right.

Another option would be to find a toolmaker that can grind a long pilot (same length as the depth of the hole) on a straight reamer for you.
You want the pilot to be the same diameter as the inside of the bush before reaming.
They have lots of flutes on them, so you wont get the biting that you would with an adjustable reamer.

The pilot part will be non-cutting, so you can mount the reamer in the drill press, lower it into the rocker while stationary, then clamp the rocker in position.
Raise the reamer again and make sure it inserts cleanly into the rocker again (ie rocker hasn't moved while clamping).
Turn on the drill press and run the reamer through gently with a bit of cutting fluid.
The pilot will keep the reamer concentric in the bush, and there wont be any deflection as the cutting load is evenly spread around the reamer from multiple flutes.

You'll still need to set up some sort of fixture to hold the rocker, but once you've sorted that out it should be pretty quick.
The end face on the rocker will be perpendicular to the bore, so for a fixture you probably only need something flat with a suitable size hole to take the pilot, and some way of stopping it rotating.

I've used piloted reamers heaps in aluminium for aircraft structural work as its about the only way you can get accurate holes by hand without complex jigs etc. I've still got a few in the shed so if it needs a piccy to help explain let me know.

Edit: the toolmaker will also be able to grind any special finished size on the reamer if the size you want isn't a standard reamer size.

Steve

Steve, I'd like a few pictures if you wouldn't mind.