Rover V8 drilling valve guides

I'm currently refurbishing a 4.0 RV8, next job up is to partly drill the valve guides out prior to pressing them out. I think they are maybe made of some sort of sintered steel. I tried a TiN coated HSS drill (12mm) this evening and it soon went blunt so will be popping out to get a cobalt drill to see if that is better.

I've also read that a masonry drill sharpened as a normal drill works so may get one of those to modify and try that.

Anyone else have any observations on the above or other suggestions please?

Is it a factory instruction to drill them out? I would have thought simply pressed out and pressed in?

I have to ask why you would want ot need to drill them out? We used to race a 3.5 and the guides were very easy to push out of the casting. These were then replaced by a much shorter set so that there was no guide in the port - good for improved flow but shorteden life a lot hence regularly replaced.

I would assume it's to preserve the fit. Every time you press something out the hole gets a teeny bit bigger. Drilling them out first reduces the bulk of material and relaxes the strength of the fit hence reducing the growth of the hole and preserving the original tolerance.

Paul.

And the replacements? One method is to bore and fit bushes inside the existing, another is to fit waisted guides (if fitted from the outside). Yet another is to knurl the guides or fit over-sized ones. I expect a loctite product would help retain guides (until the head is overheated).

Warming an aluminium head, with iron guides, will make the job a lot easier of course.

I’ve only ever replaced guides in cast iron heads, but never had a problem with pressing, or even thumping them out and in. We used to be able to ream the worn guides and fit new valves with oversized stems back in the 1970s!

There are several ways to do this, the guides are effectively steel tubes and the heads are aluminium. The Rower workshop manual says press them out using a special tool, basically a drift. Some pros heat the head up and knock them out and some machine down the guides to reduce the hoop stress where the guide fits. That leaves a step in the bottom of the guide where a drift can be fitted and the old guide pushed out.

I prefer the latter as there is little chance of pick up, which aluminium can be prone to do, and it should be easier to do this than heat the heads (and, of course the guides) up.

I have shortened guides to put in, the head will be warmed up and the guides popped in the deep freeze so all good there. Its just that the steel the old guides are made from is difficult to machine, I have experience of cast stainless and other high grade steels but this stuff has surprised me!

Heat the aluminium head to about 100C will help tremendously. If no go, you can heat as far as 200C if needed.

I sometimes use a drill to comletely remove the end that sticks out into the exhuast port so that build up on the guide does not score the hole in the head as the guide passes through it. This with guides where the end is same OD with no stepped down end.

No idea on drilling your steel guides though. Sounds like they are work hardened. You might get it with HSS running very slowly and don't let the drill rub.

Thanks Hopper, they are straight guides so they can be pushed out from the rocker side rather than drag any carbon deposits through the hole. I'll see how I get on today and report back...

A day or so ago, someone posted drills - Screwfix Bosch

**LINK**

A bit busy for a long conversation at the moment, but have you considered having the existing guides knurled internally.

My own engine builder considers it better than replacement, particularly for Rover V8s.

Bill

Thanks SP5 - No I hadn't seen that but I've got a 12mm one of those to try from Toolstation!

peak4 - Thanks also, I've never heard of that one! I have the guides ready to go in so will see how I det on with my new drill...

Feedback!

I drilled all the eight guides in the one head to 12mm dia x 40 deep using a Bosch CYL-9 MultiConstruction drill from Toolstation, catalogue # 21437. It drilled the steel guides really well, I ran it at 400rpm and provided I kept plenty of pressure on it cut nicely. I haven't finished making my coolant system yet so treated the drill to a tin of CT-90 cutting and tapping fluid, catalogue # 61138. The drill was cutting as well on the last guide as the first, so an excellent bit of kit, I may invest in a few more of these...

One down side was that the swarf comes off like needles!

There is absolutely no need to drill out the guides on any of the BOP engines, they press out easily, with the correct tools, and likewise press back in with the correct tool to the correct depth.

Replacement guides are a couple of thou oversized from standard to allow for any wear caused by the removal operation and give a tight grip on refit.

I would suggest that as the ten bolt heads are fitted with bolts as standard, you consider the use of the stud kit from ARP No 157-4301 which will allow for a better grip onto the gaskets, which should be composites on these engines rather than the metal shim type.

Are you changing the cam? if so don't forget the rocker shaft shim kits for setting the follower pre load.

Regards

Yep, going to use ARP and composites. I will be changing the cam but keeping the standard (new) hydraulic followers as it is a road engine for a TR7 and 5500 rpm will be fine. I'm looking for a bit extra performance over my current 3.5 but want it to be super smooth and very tractable.

TR7? Surely it's a TR8 or haven't you told your insurers and the DVLA?

Robert G8RPI.