Valve clearances

[Robbie693]

As part of my head gasket replacement I have been doing the valve clearances and found that the Inlets were all rather tight - one was down to .003".

Exhaust side was not so bad (around .009"), although No 1 was a bit wide, between .011 and .012.

Having measured the shims I found that No 1 inlet and exhaust had .062 size shims in them, which to correct I had to put in a .061 for the inlet and .063 for the exhaust.

These are very close to the .060" limit so it looks like I will be in the need for new seats at some point in the future..

The car has done around 10k since the head/engine was rebuilt. I have a recipt for new guides and valve lapping - no mention of new seats so maybe they weren't replaced at the time. It seems strange that the inlet clearances were more worn than the exhausts - I thought the exhaust valves were more prone to wear?

Can someone tell me what the average wear rate is for the valve clearances so I know when I need to start saving for for a head rebuild?

Thanks

Robbie

[carrierdave]

Hi Rob,
Before going to the expense of having new seat put in, try fitting a new valve. I recently had new guides along with some gas flow work. I then installed new valves and re cut the seats. All of my shims are now between 0.104 and 0.0092.
The reason I didn't go for new seats was down to mileage. I only cover some 2 - 3000 miles a year so my engine builder said that it was not necessary.

I think I have a spare exhaust valve and a set of big valve inlets - let me know if you want to try this first and I could send you one to try.

Dave

[Robbie693]

Hi Dave,

Thanks for the kind offer.

I have the engine back together now so I'll bear your suggestion about the valves in mind next time the clearances close up.

I didn't take the valves out as I don't have a spring compressor and they looked in good condition, with no leakage - so I chickend out and let them be!

The guides were replaced by the previous owner, 10,000 miles ago. This was in 1988 so I doubt they were suitable for lead free petrol. Don't know how long these will last either but I do run it on high octane with Millers VSP.

Cheers

Robbie

[rgh0]

If you still have good compression and no oil smoke but just running out of shim thickness, one way to avoid pulling the head and doing the seats and valves is to change to a thin shim pad steel bucket that will allow a thicker shim to be used.

The rate of valve seat recession can vary greatly depending on, quality of the seat and valve material, fuel used and how the engine is tuned and used. I would expect a normal road engine to stay within its 2 thou specification range for at least 20 to 30 thousand kilometres if not longer.

cheers
Rohan

[Robbie693]

Thanks Rohan,

I noticed QED supply thin buckets - I wondered if that was what they were for.

When I get the engine running I'll get a compression test done To see how things are. I found a receipt for 4 valves in my file, presumably exhaust valves, so I don't know how old the inlets are.

Looks like, if all is ok, I'll be able to actually drive the car for a bit - I've had it 2 years and only been able to do 500 miles what with one thing and another

Cheers

Robbie

[rgh0]

The thin buckets are actually for competition engines which use longer valves to fit in the spring for a higher lift cam and need a thin bucket to get shim thickness to an acceptable level in combination with a smaller cam base circle.

But also a option for your kind of problem
cheer
Rohan

[Dag-Henning]

- just be aware that the thin steel buckets are abt. 2,5 mm. longer than the std. ones, and may touch the spring base.....

Dag

[rgh0]

Some of the steel buckets are made longer by some manufactueres because they are intended to be used with smaller base circle high lift competition cams so they stick further out of the head. Standard base circle is 1.2 inch, high lift cam typically 1.1 to 1.0 inch depending on who grinds it

The longer buckets are generally not a clearance problem when used with a standard lift standard base circle cam but as with any modification you always need to check.

cheers
Rohan

[Dag-Henning]

True enough. Sorry, forgot to say I referred to the ones that QED supply.

Dag