Thread: Valve Guide Wear 3.9 - what's acceptable?

Originally Posted by aRRon

Hi guys,
Reconditioning the cylinder heads on my 1990 RR 3.9 V8 (low compression) 200,000km - half of them on gas.
Anyone know what the specification is for the internal diameter of the valve guides (after reaming)?
On the worn ones I'm getting 8.712mm (0.343").

Hoping to avoid having to replace valves.
Valves and seats look surprisingly good - no signs of recession, burning, cracks etc.
Heads removed because of blown head gasket - No. 1 cylinder filling with coolant - looked like the steel gasket corroded between engine block water gallery at front of motor and the cylinder.

Any other advice appreciated.

Don't forget that the likelihood is that the guides are not worn evenly/ parrallel. Your measurement may not reflect the true 'shape' and dimensions along their entire length.

I would strongly suggest a replacement of all exhaust guides, the valve stems need to be measured and checked obviously, but 99% of these heads we have come across only req'd exhaust guides and a reseat for all the valves. Unusual for exhaust valves to be replaced unless stem is scored from carbon etc and/ or head of valve getting too pitted to allow recutting without reducing margin excessively.


Having run Gas for 100k, I would expect the heads are pretty clean, but due to the absolute zero lubricating qualities of LPG, I would be extra vigilant with the checking/ replacing of all the valves . (Are you using flashlube?)

In short, you've come this far, valves and guides aren't a huge issue in the overall scheme of a job of this size anyway. I'd look at the situation in a 'do we want to be here doing this again in the not too distant future?' kind of light. Get a quote either way from the machine shop.


JC

Originally Posted by aRRon

Hi guys,
Reconditioning the cylinder heads on my 1990 RR 3.9 V8 (low compression) 200,000km - half of them on gas.
Anyone know what the specification is for the internal diameter of the valve guides (after reaming)?
On the worn ones I'm getting 8.712mm (0.343").

Hoping to avoid having to replace valves.
Valves and seats look surprisingly good - no signs of recession, burning, cracks etc.
Heads removed because of blown head gasket - No. 1 cylinder filling with coolant - looked like the steel gasket corroded between engine block water gallery at front of motor and the cylinder.

Any other advice appreciated.

Check your valve guide wear by rocking the valve in its open position, rock across the head as most wear will be in this plane, good Idea to replace valve guides, esp. if you are going to grind new seats, Regards Frank.

If your going to be running LPG Id go the effort of replacing the valves with stainless ones and using the same for the kliners that you put into the head.

last forever that way.

Thanks JC, Good to know what typically wears from someone who's seen lots of them. My old world thinking is new exhaust guides and exh. valves - just valves are expensive and they appear good. No scoring or pitting on the head. I did take measurements (top/mid/bottom) on each guide but guess that doesn't prove they're parallel. Have been adding Flashlube to every second tankful or so and doing 100km per week on petrol but have owned it for just the last 25000km. There were no oil seals on the guides so hopefully a bit more oil went down them as they aged. Was consuming maybe one litre per 5000km. Can I ask whether camshaft lobe wear is usually significant after 200,000km? Lifters not showing any abnormal wear patterns.

Thanks Dave, where do you source s/steel valves and liners? Are they very expensive?

last lot I sourced in townsville after lots and lots of ringing around and (from vauge memory) they were about twice the price of standard valves for the commodore they went into.

Originally Posted by aRRon

Thanks JC, Good to know what typically wears from someone who's seen lots of them. My old world thinking is new exhaust guides and exh. valves - just valves are expensive and they appear good. No scoring or pitting on the head. I did take measurements (top/mid/bottom) on each guide but guess that doesn't prove they're parallel. Have been adding Flashlube to every second tankful or so and doing 100km per week on petrol but have owned it for just the last 25000km. There were no oil seals on the guides so hopefully a bit more oil went down them as they aged. Was consuming maybe one litre per 5000km. Can I ask whether camshaft lobe wear is usually significant after 200,000km? Lifters not showing any abnormal wear patterns.

1 litre per 5000km for a 3.9 is about average actually. 200,000km I would DEFINATELY fit a cam, but seeing as the followers haven't got any adverse wear, I would say someone has already done a cam replacement. At 150,000km these cams are usually well on their way to replacement. No oil seals means that someone has removed them possibly after fitting a new cam. The initial problem with these engines stems from having valve stem seals on both inlet and exhaust, running ULP and even worse LPG, so there is absolutely NO lubrication to the exhaust guides. Combined with carbon buildup the guides get 'sticky' and cause bigger opening loads for the exhaust valves. This basically removes the exhaust lobes from the cam very quickly.
I've replaced a cam and lifters in a 98,000km old D1 that did nothing but idle around in traffic all its life, carboned up the exhaust valves and wore away the exhaust lobes, causing about 30% less lift on all but 3 of the ex valves!

When we do head overhauls and cam replacements in these V8's, I don't refit exhaust stem seals at all.

JC