Let's talk about valve guide wear

[BrazilianZ28Camaro]

Hello Gents

This matter took my attention, so I'd like to ask, how many miles would the bronze valve guides survive up to the point the clearances are too loose? Say on a SBC half street / half strip engine with max 7000 rpm.

I do understand this will vary greatelly with valvespring pressure,cylindre pressure, cam lobe design, oil, type of valve seals... I mean , what are your experiences with guide life and what engine /car combo.

Thanks

Diego

[TMSJoe]

I drove my Buick wagon for 11 years. 377 SBC flat tappet cam, stock springs, SS valves, bronze guides 186 casting. Not sure on the mileage but I used to tow my '67 Chevelle to the races with it as well as drive it as my work vehicle. I retired the car but it was running fine. I sold the heads and they are on a race car now. The block is stashed in a box trailer.

There was a time about 1992-ish when we were having guide seizures with the bronze guides. In 1994 I switch back to bronze from iron and haven't been having issues.

I think geometry and tune-up are the biggest causes of guide wear. Seems good running engines stay together longer.

[MileHighMan]

I drove my Buick wagon for 11 years. 377 SBC flat tappet cam, stock springs, SS valves, bronze guides 186 casting. Not sure on the mileage but I used to tow my '67 Chevelle to the races with it as well as drive it as my work vehicle. I retired the car but it was running fine. I sold the heads and they are on a race car now. The block is stashed in a box trailer.

There was a time about 1992-ish when we were having guide seizures with the bronze guides. In 1994 I switch back to bronze from iron and haven't been having issues.

I think geometry and tune-up are the biggest causes of guide wear. Seems good running engines stay together longer.

I agree with your comment about good running engines staying together longer....In the old days with carburators we'd typicaly see 125,000 miles before a rebuild was needed...And an overbore on the block had to be done.....Now days I see cars with 300,000 plus miles and still running excellent....The advent of fuel injection and excellent fuel control..and emissions devices makes them last longer.....Who would have thought?????.......In the early days the emissions stuff just caused problems.....Dan.

[PackardV8]

Too many variables:
1. Lift/intensity
2. Rocker ratio
3. Valve stem seal
4. Oil
5. Length of trips
6. Valve stem finish
7. Guide finish/cylindricity/seat concentricity/clearance

jack vines

[F-BIRD'88]

99% of premature valve guide ware failure happens right at the initial engine fire up.
lack of lubrication Dry valve stems. Retarded timing, hot cylinder heads.
When you get your heads take them apart and clean the guides and valve stems and oil them before fire up.
Oil the rockers too. If it don;t smoke a bit when you first fire it up the first time, not enough oil in the guides.
Oil is your friend.

[77cruiser]

I've got about 20K mile on my AFR heads just had a touch up valve job done & the machinist said he had to hone a few guides cause they were tight. So I'm guessing they'll last a long time if they keep getting smaller.

[MotionMachine]

I also stopped using solid bronze guides in cast heads on exhaust years ago because of the seizure problem. Never an issue in aluminum. I'm convinced that it's a heat transfer problem in cast. Maybe when the guide is pressed in the head the guide collapses some on the leading end therefore losing press fit and proper heat transfer from the valve to the guide to the head? Whenever a head comes in that seized a valve, the guide od is reduced by several thou on the chamber end and the od is black from exhaust blowing halfway up the guide. Since I changed to liners, with one exception, I've never had to replace a liner that I had installed previously.

[PackardV8]

I also stopped using solid bronze guides in cast heads on exhaust years ago because of the seizure problem. Never an issue in aluminum. I'm convinced that it's a heat transfer problem in cast. Maybe when the guide is pressed in the head the guide collapses some on the leading end therefore losing press fit and proper heat transfer from the valve to the guide to the head? Whenever a head comes in that seized a valve, the guide od is reduced by several thou on the chamber end and the od is black from exhaust blowing halfway up the guide. Since I changed to liners, with one exception, I've never had to replace a liner that I had installed previously.

One other explanation is bronze expands at almost twice the rate of cast iron. Since the head is stronger, the bronze is crushed on the OD. Because it reaches the outer crush limit and cannot expand further outward, so it expands inward as well, grabbing the valve.

The reason no trouble in aluminum heads is the expansion rate of aluminum more nearly matches that of bronze, plus the crush resistance of aluminum is less than iron and the crush from guide OD expansion is shared by the head.

jack vines

[novadude]

What do you guys use to lubricate guides / valve stems when assembling heads? I am mostly interested in iron guides (OE Vortecs), but I would be curious to know if you use the same assembly lube / oil / grease when assembling heads with bronze guides.

[DaveMcLain]

On assembly I always use MPZ from Torco, that red stuff. It seems to stay put and not cause problems. Some cylinder head manufacturers use white grease or lubripate which seems to work fine too. Regular engine oil should work well but something thicker might be better if the cylinder head or engine has to sit around for a long time before being fired for the first time.

What I always find to be interesting is when I take the headers off after running an engine on the dyno. How can the stem and guide be dry or nearly so and free of oil yet survive, I think it's miraculous.

[panic]

8. length of the stem inside the guide (high = good)
9. distance from the seat to the guide (low = good)
10. ratio of rocker arm lever length to lift (high = good)

[BrazilianZ28Camaro]

I've got about 20K mile on my AFR heads just had a touch up valve job done & the machinist said he had to hone a few guides cause they were tight. So I'm guessing they'll last a long time if they keep getting smaller.

Very interesting! Your heads have 8mm stem valves???

[BrazilianZ28Camaro]

Since I changed to liners, with one exception, I've never had to replace a liner that I had installed previously.

What interference fit you set on the liners at assembly?

[BrazilianZ28Camaro]

the expansion rate of aluminum more nearly matches that of bronze, plus the crush resistance of aluminum is less than iron and the crush from guide OD expansion is shared by the head.

jack vines

That means that only God know what will be the guide running clearances.

I believe this expansion should be small like .001 to .0015" due the coolant cooling the guide areas

[T-flow]

Clearance and what oil? These two have shown most of the problems that I've seen.


T-flow