Are these valve reliefs on the 3.5 pistons - pic

**high888** · 11-25-2007, 03:11 PM

I found this picture of somebody who had removed the cylinder head off of a 3.5L. Notice the notch (actually 4 of them - one each for the 4 valves per cylinder). I have read a couple of older articles about Chrysler 3.5's, and both said they have valve reliefs on the top of each piston. You ask, "High, what is your point"? Well, the 3.5 has a fabric/rubber timing belt driving the overhead camshafts. If it breaks, the valves no longer time up with the pistons, and "boom" they meet. Valve reliefs are a notch so this will not happen, and the engine simply freewheels with no damage. Any experts out
there who can verify if this notch is in fact a valve relief? I can't image what else it would be.

**PaCharger** · 11-25-2007, 03:17 PM

Identical spots on both cylinders..I'd say yes. Had this happen on a VW Scirocco (wifeys when we met) when the timing chain went....looked just like this....

Took out 2 valves too....

Sorry bud.

**bipto** · 11-25-2007, 03:42 PM

From the pics it does not look as if the reliefs are cut flush with the top of the piston - it looks like there was impact.

Interesting - I didn't think the 3.5L was an interference design. Perhaps it is...

**high888** · 11-25-2007, 08:32 PM

Originally Posted by PaCharger

Identical spots on both cylinders..I'd say yes. Had this happen on a VW Scirocco (wifeys when we met) when the timing chain went....looked just like this....

Took out 2 valves too....

Sorry bud.

I think you are missing my point. This isn't my engine. And this engine did not break the timing belt. It was opened up for some other reason. Those
indentations are not from valve contact. They are machined into the top of each piston. That is my question: are they valve reliefs, as what else could they be?

**high888** · 11-25-2007, 08:36 PM

Originally Posted by bipto

From the pics it does not look as if the reliefs are cut flush with the top of the piston - it looks like there was impact.

Interesting - I didn't think the 3.5L was an interference design. Perhaps it is...

Again, there was no impact on this engine. The belt did not break. No valve impact could cut grooves that deep or that perfect of a pattern. Plus, when valves do hit the piston, virtually all damage is to the valve, i.e. bent valve
stems. Anybody else care to comment?

**bigjim** · 11-25-2007, 10:14 PM

First generation 3.5s (93 - 97) had relief machined into the pistons so they could free wheel. Second gens (98 - 2004) were interference engines, they will crash valves into pistons if the belt breaks. I have NO idea what is in the third gen (2005 on) is. I will wander some texts and get back to you.

**lafrad** · 11-25-2007, 10:25 PM

They ARE reliefs, but they are cut so there is clearance when the cam is working properly.

they are NOT deep enough to free-wheel when the timing belt breaks.

**PaCharger** · 11-25-2007, 10:38 PM

Okay, so you are telling me an engine mfg made sure to cut arcs for exhaust and intake valve for each cylinder rather than building enough tolerance for another .050" space?

WTF? Honestly learned something new tonight. Thanks for sharing...I'm going to research and read. 40 and still learning....

**bigjim** · 11-25-2007, 10:39 PM

From page 9-1495 of the service manual

CAUTION: The 3.5L engine is NOT a free-wheeling
design. Therefore, care should be taken not to
rotate the camshafts or crankshaft with the timing
belt removed.

**bigjim** · 11-26-2007, 06:23 PM

This is a pic of a first gen piston, not a great shot but... I took this of the engine I bought and had intended to use for a build up for my '97 Intrepid this spring. After breaking it down, it was clear it was NOT useable in sooooo many ways.

**lafrad** · 11-26-2007, 06:37 PM

Originally Posted by PaCharger

Okay, so you are telling me an engine mfg made sure to cut arcs for exhaust and intake valve for each cylinder rather than building enough tolerance for another .050" space?

WTF? Honestly learned something new tonight. Thanks for sharing...I'm going to research and read. 40 and still learning....

250 hp outta 214 ci... gotta get it with good valving and port design... It just means the flat-top pistons would interfere with normal cam operation.

Grind the reliefs and you get the desired effect. unfortunately, the reliefs aren't big enough to allow free-wheeling.

**high888** · 11-26-2007, 07:11 PM

Not the answer I was looking for. I once owned an Acura, and the belt let go at 50K. After warranty expiration, of course. Bent up a bunch of valve stems. $1200 repair, and that was 20 years ago. The owners manual recommends the 3.5 belt be replaced at 100K. Right. I think I will go conservative and do it MUCH sooner than that. That is if I still own the thing.

THANKS, Big Jim for doing the detective work.

**high888** · 11-26-2007, 07:17 PM

Originally Posted by lafrad

250 hp outta 214 ci... gotta get it with good valving and port design... It just means the flat-top pistons would interfere with normal cam operation.

Grind the reliefs and you get the desired effect. unfortunately, the reliefs aren't big enough to allow free-wheeling.

Wow, those are some tight tolerances if those reliefs are just for normal piston and valve travel. The compression must be pretty high for this 3.5
if the pistons are getting that close to the valves when the valves are fully open. Not much margin for error.

**ZMagnum** · 11-26-2007, 07:44 PM

I believe that first pic is of 36 Chamber's engine. His timing belt got shredded and it messed up his engine real bad. I believe he was under warranty.

Fnky and others have said if you are getting the timing belt replaced on the 3.5L get the water pump replaced as well. Both are driven off the timing belt.