How much slop is normal for the vavle guides? When I was shimming my springs I could move some of the valves side-side in the guide a little bit. Is this normal? It wasn't anything huge, maybe .005", you could feel it hit each side of the guide.

 

I'm just guessing and will check my service manual when I get home, but
.0045 comes to mind as a maximum. I'm not sure what the service limit is,
but I'll revise this later once I get home and check.

Oops... revised to correct the number. What's being off by a factor of 10
among friends. DOH! I also did not find anything for an LT1 valve guide
service limit.

 

http://www.aa1car.com/library/ar696.htm

 

How many miles are on the heads? Has the motor been running lean?

I would think that the service limit is .003" but I would consider a guide in serious need of replacement after .0025". It is hard to wiggle the valve in the guide and determine what the clearance is unless you have lots of experience with comparing your "feel" to an actual bore gauge reading - I can wiggle a valve and guess within a couple tenths (.0002) where the clearance is at as long as it is between .0005" - .0025, bigger than that just feels loose as your ability to feel the clearance gets more inaccurate the clearance increases.

Some diesel motors use a side wiggle spec - the deflection measurement of how much you can wiggle the valve. I would think that if you can feel movement at the top of the valve with oil in there taking up clearance, that it is something to be looked at - there is power lost in increasing guide clearance.

 

I have no idea how many miles are on them, the car has 98K on it but it had ported heads on it when I bought it so who knows. The motor hasn't been running lean at all. Some you can barley move, others you can move and see a tiney gap when you push them to the other side.

 

Yeah, if you can feel the valve wiggle it's probably out of spec. Good race VJs are down to .0010" guide clearance or even LESS!

Only way to tell is to measure them!!

Bret

 

How much would it hurt performance if they are out of spec a little bit?

 

Just going to eat oil and beat out the VJ.

Bret

 

David Vizard talks about this in one of his books, in testing done on a 4 cylinder pinto engine he shows from a baseline of .0015" clearance compared to .004" there is a 3 hp loss, and with .006" it goes to 10hp, he also states that the V8 would loose twice that amount(double the valves)

The more important point is that you should not be wearing guides out to that extent in a EFI motor with less than 100k...there is something causing the wear - too lean, too rich...vacuum leak, exhaust backpressure, all those can lead to guide wear; and as guides wear, the rate of wear increases the more worn they get.

 

So can wrong pushrod length. Check rocker tip to valve pattern with the 'dry erase marker' techniqe to make sure it's centered correctly. Search 'check pushrod length'.