Valve stem height

[DarthBuick]

I got my heads back from the machine shop and placed a straight edge across the valve stems and noticed three valves .011 higher than the rest. Is this too much for lifter preload? I think he should have checked this.

 

[turbodave231]

If I am paying for a valve job, I'd prefer to see my valve stem height very close to each other......but

The valve installed height spec is 2.030 to 2.080 (Going from memory here). That gives .050" of room for all valves to be in spec and still have the lifters operate in the middle of their travel. As long as your machinist kept within this range you should be good. Most hydraulic lifters have a range somewhere around .150" . Plenty of adjustment if pushrod length is correct.

 

[fastblackracing]

I got my heads back from the machine shop and placed a straight edge across the valve stems and noticed three valves .011 higher than the rest. Is this too much for lifter preload? I think he should have checked this.

It is very common for the say the exhausts to be a slightly different height than the intakes when the valve job is done. Excessive valve seat grinding sinks the valves further into the throat and this is bad for airflow and uses up precious metal for future valve jobs, but all of the exhausts should match and all of the intakes should match. Were all of your lntakes the same or was it mix and match

 

[turbodave231]

Correction:

I just looked in the AERA database and discovered that my memory isn't that good............found the correct stem heights for the 1986-87 Buick v6:

1.9350-1.975" for both intake and exhaust. So the engineer specified a .040 window where valve stem height can fall in production.

This is also a very important spec to adhere to because it affects rocker arm to valve tip contact patterns. And as stated above, sinking the valve into the seat screws up airflow.

It is always a good idea to check for proper pushrod length and valve tip contact pattern
There are many variables that will change the length needed for the pushrod. These include but are not limited to:

• Decking the block,
• Milling the heads
• Using a head gasket different from the stock thickness

 

[DarthBuick]

The three that are .011 higher are exhaust and he replaced 3 exhaust valves. This is why I always double check. I will have them shave .011 off of the stem if needed. My head gasket thickness is going to change also. It did have .045 solid copper gaskets and O-ringed heads and will now be using .060 compressed gaskets.

 

[Mike T]

Any guesses as to what could cause excessive scrub when the stem height falls within the specified range ? I also have excessive wear on the bronze liners in just 10k. The height appears to be between 1.945-1.950 on the head that I'm measuring now.

Another thought......since the height is correct maybe the guides were loose all along and caused the excessive scrub on the tip of the stem ???

 

[fastblackracing]

How much cam lift, spring pressure, and what rockers and oil are you using? and if its stock rockers what shafts are in it?
Excessive pressure/friction between the rocker and valve along with bad rocker geometry and possibly an oil issue with insufficient high pressure strength can cause this...... any pics?

 

[Mike T]

I have T&D rollers, cam was a flat tappet with 108# springs installed @ 1.750 (went roller cam this time), oil was Valvoline 10/40 with zinc additive.
The guides are k-liners in iron 8445 heads and at .500 lift the valves can be rocked on average about .010 or so.

The contact patch hits close to the middle but measures between .080 and .090 wide. I'll get photos tomorrow.

 

[Mike T]

Finally got a couple of pics.

 

[gunzandgearz]

The valve on left is spot on, valve on right is probably going to wear on guide.

 

[Mike T]

Two valves have a slightly off center contact pattern......I would suspect that the guides (K-liners) are off and I wouldn't think there would be enough room to re center them since the K-liners are so thin??? The off center is a concern but the .090 wide sweep/scrub has me scratching my head since the stem height is correct.

It seems as if geometry correction is very limited on shaft type rockers with the fixed fulcrum point.

 

[gunzandgearz]

There are several things that change this relationship between valve stem and rocker, valve seat[sunk seat or too many valve jobs]material taken off valve tip.This is one reason that I love, and a lot of people switch too ,is the small and big block chevy stuff, a lot of adjustability.You could fix that but like anything else in life just add money. You might be able to cheat system a little and install lash caps or try just a little different length pushrod,but if it were me I would try to find exactly where the problem is and address it, because as you said not much adjustability with this type of system. The one valve where the valve sweep starts is almost where it should be ending, you might try installing an adjustable pushrod too a little shorter than what you have on that valve and sweep it,I like to use gear checking compound as it is yellow and shows up great, if it works, pushrods are cheap, compared to alternative.

 

[Mike T]

you might try installing an adjustable pushrod too a little shorter than what you have on that valve and sweep it

Correct me if I'm wrong but I can't see pushrod length changing sweep on our shaft type rollers?
It seems as if stem height and the perch that the rocker assembly sets on would be the only thing that could change this?

 

[turbodave231]

You are right, changing shaft height is the only way to adjust pattern on a shaft system. I have heard of guys shimming the shafts up, but that is not a good solution in my opinion. lash caps would put you WAAAY out of the ballpark. The thinnest caps I've seen are .050. Pushrods have NO effect on tip contact pattern on a shaft system.

What rocker arms are you using?
I would expect T&D or Harland Sharpe to be very consistent from rocker to rocker, but stock rockers are NOT all the same. How do I know this? I assembled an engine with lightweight check springs and measured lift at the valve with a dial indicator. I measured well close to 200 stock rockers to find the best set of 12. They are literally all over the map in lift/ratio which Will affect your pattern.

As an idea to identify the problem, Swap the rocker with a poor pattern into a location that previously had a good pattern. Do another pattern check. Does the poor pattern follow the rocker arm, or stay with the valve regardless of the rocker used?

 

[gunzandgearz]

Changing the height isn't going to work either because that moves all of the rockers which will also change the ones that you have a good pattern on, youre just chasing your tail. I agree that doing the shorter pushrod will not change the sweep but if you only shorten the the ones that are off it should narrow that sweep pattern which might help, but it will also decrease your lift on that valve a little. This is just something you are going to have to play with because as I said in my post there isn't really any adjustability in these systems

 

[Mike T]

I see now why the machine work needs to be near perfect on our heads.

A while back we were doing a side by side comparison of my home ported heads to a set from a well known shop. In general we were just looking at port size, shape and taking a few measurements. It didn't occur to me at the time as a big deal but the stem heights of the high dollar heads were .100 higher than mine. I now know that mine are very close to spec and still have a less than desirable wear pattern so I can only imagine what +.100 will look like.

 

[gunzandgearz]

I agree and its probably one of those areas where I wish buick would have taken a page from the chevy playbook.It sucks to say this but you would probably be better off buying a set of aftermarket heads because by the time you spend the money to fix them youll probably have more in them than a new set.ON the flip side you may be right and the guides might have been already worn out but either way your going to be out a lot of money. Good luck hope it all works for you.