Dent in Piston !! Check it out....

[Jandrews]

Still searching for the cause of the low compression in the RS Motor... I pulled the heads today and here is what I found:

The exhaust valve relief cut in the piston has a dent in it from when the valve came up and gave it a kiss!! This was not mentioned to me when my "mechanic" "repaired" this head last year. The bottom lip of the exhaust relief cut appears to have been "smashed" by an approaching valve. Also note the rough texture of the upper part of the same relief cut. Not sure if someone "smoothed" out a similar spot there, but it does not look right either.

Not sure this would cause my low compression however. The exhaust valve was tight (no clearance), when I checked it, but again I'm not sure it was tight enough to leak compression. Next step will be disassembly of the heads to witness the "quality" of the head work that was performed at the same time as this mess!!

By the way, I found RTV rubber gasket sealant on the camshaft sealing flange and oil return tubes. I don't believe either of these are supposed to have that goop on them!

I also included a picture of the valves in the head. The exhaust valve looks very lean and dry (light brown) compared to the rest of the engine. Not sure if that is because it is "newer", or if that may be an indication of where my problem might lie.

Any thoughts on what I ought to do with all of this?

Thanks,

JA

[jkeyzer]

The pics are not showing up for me. Anyone else?

[glickster]

I can't see the pix either.

[Early_S_Man]

Just little boxes with an 'X' in it!

JA ... you need to rename those files without any blanks in the filenames! And, upload them again!

[Jandrews]

Aha...

Thanks for the tip, Warren!

I knew there was something wrong with the pictures not loading, but I didn't know it was from spaces in the filenames!

I am at my brother-in-law's house right now, so I don't have access to re-upload the pictures just yet. I will do it as soon as I get home.

Sorry about the bad links.


JA

[Jandrews]

Let's try this again...

Also, can anyone identify these pistons?


Thanks,

JA

[Jandrews]

Hmmm...

Not sure why the pics aren't working. No spaces this time, but still only getting the X's.

Any ideas what might be causing this? All the pics are in .jpeg format and are below 100k.

JA

[Jack Olsen]

Still not working. Spaces cause problems for some browsers (like Netscape 4). But the thing that's messing you up, I think, is that all of your file names use the # (number sign) in them. Rename them without that character, and send them again.

[Jandrews]

The power and knowledge on this board still amazes me...

Thanks Jack. Your suggestion makes sense. Now let's see if it works...


JA

[Early_S_Man]

JA,

Those are just your standard group 2 sized forged Mahle RS piston and Nikasil cylinder ...

It would be very hard to tell whether or not the 'zero' clearance was holding that valve open or not ... unless you put a dial indicator on the retainer before you loosened the adjustment on the swivel foot and watched to see if the position changed as you backed off on the swivel-foot.

My guess is that it was holding the valve open, and that was the cause of the low compression!

[jkeyzer]

If the valve was being held open, it wouldn't cool properly, and that would lead to the light tan "lean" deposits shown in the pictures, right?

[Wayne 962]

Hmm, the deposits look semi-normal to me here. There is definitely some evidence of impact with a valve at some time in history. However, if the engine is assembled correctly, most of the time the valves and pistons will not bend. Instead, the interaction between the valve and the piston occurs along the axis of the valve. The most common result is that the rocker arm breaks. Typically the valve and piston are left undamaged. However, I would still suggest checking it when this happens.

Note that this only happens with the non-CIS and non-Motronic pistons - the CIS and Motronic-shaped pistons will bend the valves on impact...

-Wayne (supposedly on vacation...)