Valve Guide Loose in Head - Options?

[ukkid35]

Having removed the valves I have found that one of the valve guides isn't worn as such, but rather it is very loose in the head

Are there oversized valve guides?

What do I need to keep in mind when I take the heads back to my preferred engineer (Roland Alsop as previously recommended by Charlie at SRR - they did a great job a couple of years ago at re-surfacing the heads the last time)?

[ukkid35]

stevieturbo said:

Although why a guide has come loose in the first place...would be of more concern than it actually being loose.

I doubt it's pure chance that it's the same cylinder that there were some serious issues last time

Fire ring distortion



Pitting before head skim



Fire ring seal damage

[ukkid35]

227bhp said:

For what?

That looks like detonation damage btw and i'm very doubtful it had anything to do with a loose guide.

Agreed, but probably either caused by pinking/detonation, or has a common cause

Oversized guide because there's no way a direct replacement is going to stay in place

[ukkid35]

Since the pitting is no worse than before, I'm going to bet that changing a faulty injector has almost fixed the pinking issue

Getting the cam timing right has helped a lot too, but I'm not claiming the pinking is completely banished

Perhaps the fact that cylinder's intake is the closest to the crank case breather is a significant factor too

[ukkid35]

227bhp said:

For what engine ffs.

AJP8

[ukkid35]

Thank you, that is fairly reassuring

Since I certainly don't know what I'm doing I'm intending to hand this over to Roland Alsop again and let them suggest options

The head skin they did a couple of years ago was so subtle I could hardly tell apart from the surface

[ukkid35]

Mignon said:

Your problem should be simple enough to fix for an expert with the right equipment but then most things are easy when you know how. I can't help you in person as I don't do this stuff any more but you might want to consider Peter Burgess who posts in here sometimes. I know he can also make special one-off guides if that needs doing. Otherwise simply give the fits I specify above to whoever you choose and hope they can measure things properly and follow them.

Many thanks for taking the time to reply in such detail, I really appreciate that

[ukkid35]

Thanks again for all your contributions to this thread

It's possible that my description of the valve guide problem wasn't so clear

Hopefully these two pics show how bad the head distortion is





This is the intake rather than exhaust

[ukkid35]

227bhp said:

Has a valve guide come loose? If so which one?

Open each pic in a new tab and switch between tabs for a crude animation - all will become clear!

[ukkid35]

Mignon said:

The chamber doesn't look too badly detonated. That guide play is very strange. It needs an expert examination first to try and determine what has happened. Keep us posted please.

Those pics were taken immediately after the head skim three years ago, it looked worse before

I imagine the guide was already loose by then, I didn't remove valves to check

[ukkid35]

227bhp said:

Why have you taken it off again? To clean the swarf out?

I'd like to understand that too - so it will become the subject of a separate thread

https://www.pistonheads.com/gassing/topic.asp?h=0&...

Edited by ukkid35 on Friday 9th March 14:09

[ukkid35]

I dropped off the heads and discussed the issues with the engineer who didn't seem at all phased by the loose valve guide, but he did say:

• That's not a five minute job

• The new valve guide will have to be custom made

• You'll need to replace the Exhaust Valves as the stems have worn so much (I was only planning to replace the Intakes because they've all stretched so much)

• We may find the guides are within spec with new valves

• You should still get the heads skimmed (I hadn't planned to as the fire ring areas looked OK)

[ukkid35]

That is a monster - how much does it weigh? Three tons?

[ukkid35]

No real chance of it falling out, but I'm sure there's a catastrophic failure mode in there somewhere

[ukkid35]

Mignon said:

Your photos make it look like the guide bore is like 1mm bigger than the guide but I would have said that's impossible.

Actually I think that's a fair description

I really don't think I have many options as there are no spare AJP8 heads

There were perhaps 2000 pairs made in total, and some of them are 4.2 and some are 4.5, I know they are different, but I don't understand what the difference is

In theory you can junk the AJP8 and fit an LS crate engine, people seem to budget about £8k and then spend twice as much making that work

I am not inclined to do that, and even if I were it would take me several years to be able to fund a conversion

[ukkid35]

stevieturbo said:

This engine seems to have had a hell of a rough time.

Who built it and what sort of usage has it seen ? Has it ever been tuned correctly ?

Normally aspirated or has someone added boost ?

This particular engine?

When I bought the car seven years ago it was the perfect example of deferred maintenance

I have run it on a budget since then, gradually replacing parts as and when I could

It was over pressurising the cooling system when I bought it, so the first thing I did was pull the heads

The most of the liners have several tide marks so the engine has sat with coolant the the cylinders several times

This correlates with the low recorded mileage between MOTs when I bought it

Also most of the intake buckets were dished because the valve clearances had closed up and the shims had'd been replaced

After replacing the head gaskets the first time, it was mapped primarily to try to address a pinking issue at 2k

It produced healthy figures on the dyno and is absolutely standard apart from short induction (because the standard hoses cost over £500, and the short kit was half that - I am on a budget)

However I suspect the fuel injector was already faulty, but I didn't discover that until I had them flow tested three years later, the next time I had to pull the heads

The car has been regularly tracked since I bought it, and the engine is routinely red lined, so yes it probably has had a hard life

Since the engine has about 60k on it, I am now coming to terms with the fact I will have to replace all valves and springs, which means my parts cost for this job is going to be about a grand, and that doesn't include any of the engineering work

[ukkid35]

GreenV8S said:

The internet suggests they designed in just about every other problem you could imagine in the valve train so it shouldn't be too surprising if they included this one too.

Perhaps you are thinking of the Speed Six and the poor Finger Follower quality control

As far as I'm aware the AJP8 has no valve train issues

In fact the very light 16v design means it is pretty robust and revs freely to 7600

The only proviso is that the shims need to be checked and adjusted more frequently than the official 12k service interval

I do it twice as often, and there is always work to do on the Intakes as the valves stretch

Exhausts are far more stable, they don't seem to wear the valve seats

[ukkid35]

PeterBurgess said:

Interesting about valve clearance disappearing, where does it go? Does the inlet seat on the insert recess or does the insert move up towards the valve guide, maybe the valve itself mushrooms over?

The new intake valves are shorter than the ones I've removed

I presume that means they have stretched (it also seems to be the consensus of the TVR crowd)

I had to drop them off as soon as I bought them so I haven't been able to measure them, but I did compare lengths very crudely while sat on the dash in the car

[ukkid35]

PeterBurgess said:

To be honest the seats look in very poor condition for a modern engine.

Shortly before I stripped the engine down, the car had an intermittent fuelling problem that meant it went in to a sort of over-rich limp home mode

I think that is why everything looks so sooty

[ukkid35]

stevieturbo said:

Are the new valves the same make/part number as the ones you are replacing ?

That could account for height differences.

With a cursory glance I couldn't see any etched markings on either new or old, there are only a couple of suppliers of AJP8 parts, I suspect they all come from the same source

Several years ago I tried to find out where the buckets come from, assuming they were not AJP8 specific, I didn't get anywhere at all

However I did find that some used ones I acquired were a few grams different in weight, I made sure I used a set that all matched

This is obviously one of the ones I eventually threw out