Is there a way to check to see if the heads are warped?

 

They would have told you when they were skimmed after the welding.

 

You could mount the cams without the valves (don't want spring pressure on lobes) and check how freely they rotate. Otherwise it would take more sophisticated measuring capabilities than you are likely to have at home.

Or as just mentioned, a good shop should have checked before surfacing.

 

I've got a pretty high threshold for dealing with frustration, but this car might be the tipping point. This evening, I assembled the passenger side head (off car) without the lifters, and spun the cam shafts. The exhaust cam shaft spins relatively freely...it requires some effort (not overly forceful), but it feels smooth. The intake cam shaft is a whole lot harder to turn...its not sticking, but probably requires 2 to 3x the effort to turn, and its not as smooth as the exhaust cam shaft.

I pulled out my Starrett straight edge, and took some feeler measurements of the top surface - best way I had to check for straightness. I found that when I pushed the left side of the straight edge down to make sure one side was bottomed, I was able to slip a .10mm to .15mm feeler gauge under the straight edge on the opposite side (area shown in the yellow box area on the photo below). The blue lines came in at zero (or not able to pass a .04mm feeler gauge - my smallest - below the straight edge). Same for the lowest red line. Taking things one step further, I removed the intake cam caps one-by-one, from front to rear and found the cam shaft resistance dropped.

I can't seem to find any info on how true a head should be, or if .10mm -.15mm is a lot of deviation, but given the resitance, I'm assuming I've got a pretty serous problem. Any thoughts or suggestions on next steps / how to move forward from here would be really helpful. Thanks - Dave

<<< REAR.............................................................FRONT>> >
http://www.flickr.com/photos/51967142@N00/8320118047/

 

Hopefully you had white lithium or some form of lube on the bearing surfaces when you did that test. Did you use original or new bearings?

I don’t know how much “friction” can be tolerated in this area. It might just wear in as it runs and be fine. Or, it might score the bearing and cause all shorts of problems.

It is not uncommon to line bore the cam mounts in a situation like this but I don’t know what bearings are available for the 928.

Maybe GB will chime in; I would think he should know.

I hope it is nothing serious and costly to remedy.

 

These don't use bearings. They use journals.

I would look at it with a dial indicator to see how far out it really is.

 

Yes, I am ignorant and don’t know what I am talking about.

My motto is that my day has been wasted if I didn’t learn something.

So how is this issue dealt with on these heads?

Thank you.

 

You might want to look into adding the metal oil pins while you are in there. Maybe someone can shed more light on since it has been a while , but there was an update to add some pins to reduce valve noise and improve oil flow in the valve train. I know I got the kit from Roger and it is only a few bucks.

 

If these heads are seriously warped then it will be cheaper to get a new set. Or go to the machinist/welder and see if they will right the situation.

It will require some welding on the journals, along with a line bore.

 

They often have to straighten heads after welding. The straightness should have been checked before skimming. How is the other head?

Also were you able to determine which cap or caps are tight? Have you and I don't want to tell you how to suck eggs made sure you have each cap back on their correct position, they are numbered to their respective positions.

 

Don't throw the baby out with the bath water just yet, this problem can be rectified. I wouldn't reuse the same machine shop as this is a basic mistake. As I mentioned in my other post how is the other head?

The worse case scenario is you'll need a line bore. How they do this is take around 1 thou off the caps and then run a boring bar through the journals and bring it to spec. While the heads were disassembled were the valve guides checked? The exhaust is normally subject to more wear especially if low ZDDP oils have been used. I say all this because if a basic mistake like what you describe has been made I would need to check everything again.

Best case scenario is, they straighten the head and re-skim head. You may need to reskim both heads for equal compression.

 

Thanks for all the help / suggestions guys. I've written answers to the questions posted, but I'll also give a brief summary here too. I tested the other head (driver side) using a straight edge and feeler gauge, and found it to be true to at least 0.04mm (my thinnest gauge) all around. I then installed cams shafts on the driver side...they seem to spin smoothly, with limited resistance. Going forward, I was debating grabbing a set of v-blocks to test the cam shafts for run out to rule out any chance that its not the head...though the straight edge numbers are certainly pointing toward a head issue. Still undecided about this, but I am grateful that the driver side numbers looked better.

I lubed up the journal surfaces with a coating of assembly lube.

I'm also hoping it can be rectified quickly and cheaply. These heads were the last thing standing in my way for reassembly. All other parts on the engine are prepped / assembled and ready to be 'dropped in'


I'm not quite following how to use a dial indicator to do this...I've always used them for run out / vertical change style measurements. Can you explain how you would take the measurement with a dial indicator?

Agreed. When I opened my cams, I found one of the old style plugs bulging. Roger set me up with a set of pins which are ready to go in.



Thanks again for all the help...off to bed now. I'll have to pick this up in the AM.

 

use of the dial indicator would require a milling machine table to secure the head to.
Then you attach the dial indicator to a fixed point and move the head around measuring run out on the pieces.

 

With the cams out, try putting your straight edge across the cam journals & put pieces of cigarette rolling paper under the straight edge at each journal. Then pull on the papers & see if any pull easier than others, indicating a possible warp & needing further checking by a top journeyman machinest. Just a quick way of checking with common tools.
The papers are very thin & flexible. I'm not sure
exactly how thick they are, something like under .001- you could always check with a mic.

 

If one entire head is good and one head has one tight cam, could you swap the tight cam with the cam from the other head? If it follows the cam, you have your answer. If it stays with the head, you have to determine if it is acceptable or if machining is required.