Dr34m

Hey everyone!

Original thread: https://www.thirdgen.org/forums/elec...ble-relay.html

To sum it up, my car stopped working while driving. For about 2 weeks i thought the cause of the problem was an electrical problem, but now i have concluded that the timing chain is responsible.

I have decided to start my project on performing the timing chain replacement (and documenting it here), but before that i have a question. 2 of my friends who are mechanics said that it is plausible that the valves might be bent. My questions are:

1. Is it possible that if a timing chain breaks or skips and the engine doesn't give sparks anymore, that the valves have been bent.
2. If the valves are bent, is there a point to change the valves (cost-wise)?
3. How to check if the valves are bent?

Thanks!

AlkyIROC

1: yes the valves are probably bent. With a lifter sitting on a cam lobe and the camshaft not turning, a piston will hit a valve. If the timing chain has jumped then the valve timing is not correct and a piston will still hit a valve.

2: Unless you have some type of aftermarket head, it will probably be cheaper to just change the heads with some factory style replacements.

3: You can start by doing a basic compression test. A bent valve won't build pressure but if the camshaft isn't turning then this method won't work. Best way is to pull the heads and look at them or with the heads off, put a solvent into the ports to see if it leaks past the valve seat. You can also take all the rockers off which will seat all the valves. Use a compression tester and put some shop air into the cylinders. If the piston gets pushed down then the valves are probably seated good enough to say they are not bent. A bent valve will allow the shop air to exit out the intake or exhaust since the head of the valve isn't seated properly.

If you have bent valves, you probably also have piston damage. Depending on how much damage, it may be a lot cheaper to just buy a replacement engine.

Dr34m

Thank you for answering! Okay so we can agree that there is a possibility (high one) that some or all of the valves are bent. I will try to google and use your information in determining how many are broke.

Now my questions comes to cost-wise. Since my engine is a V6 it means that it has 6 intake valves and 6 exhaust valves. Im trying to make a damage-control evaluation. From rockautoparts it says that about 12 valves costs 35 bucks more or less. Can you please tell me what kind of parts do i need to change besides that? Currently i know only this information:

1. 6 intake and 6 exhaust valves cost about 35 bucks.
2. *EDIT* Okay so pistons as well, the complete piston assembly.
3. *EDIT* Okay i have made some damage-control and it seems i know what kind of things need to be checked and such. When i will start this project i will keep you guys post-poned with pictures.

RamIt

I don't think the V6 is an interference engine. The V8 surely is so you might have avoided a big problem.

Dr34m

One thing i can say is that i could crank the engine after it shut off and i didnt hear any metal sounds and it cranks fine, just doesnt start. Im going to research if it is an interference engine. Back in a bit.

*EDIT*
2.8 V6 engine specs:
CAMSHAFT
LIFT
Intake 6.67
Exhaust 6.94

VALVE SYSTEM
STEM CLEARANCE 0.026-0.068

CYLINDER BORE
89
STROKE
76

*EDIT*
Got some information from this thread: https://www.thirdgen.org/forums/v6/3...ce-engine.html
Some guys have tore apart the V6 engine and said 100% its a non-interference engine. I guess thats why i dont hear any metal sounds when cranking the engine. Even after the problem started. I will still check them, but i will be honest, a little bit of happiness instilled in me .

AlkyIROC

Cost of the valves is nothing but you can't just take out the old valves and replace them with new ones. Depending on how much wear there is, the guides may be worn and require replacing or at least need to be resized for new valves. Valve seats will also need to be resurfaced for the new valves or the new ones will still leak. When heads get a valve job, the valve spring pressures are also checked and your engine may require new valve springs. A good machine shop will also resurface the head to make sure it's square and flat.

Like I said, it may be cheaper to just buy fully assembled replacement heads.

OrangeBird

iTrader: (1)

I posted this to your other thread .

Alky , you do realize this is a 2.8 six , and not an eight , we're talking about here , yes ?

paulo57509

GM 60-degree V6's (2.8, 3.1, etc.) are interference engines.

OrangeBird

iTrader: (1)

Can you cite any actual GM data on this ? I ask only because I've had my own chain break and some years ago a friend with a Camaro 2.8 had his chain break , and neither engine ruined the valves ? I personally replaced both chains , both engines ran fine afterward , and mine even to this day blows respectable compression readings every few years when I check it . (friend sold his Camaro a while back still running good)

Did you have a 2.8 hit the valves or have you known of any ? just know , I'm not attacking you here or looking for an argument , I just want it put to rest one way or the other , maybe if the cam stops in one certain position only it his them ? This don't seem likely but I'm looking for reasons why I have experience with two broken chain 2.8s and no hit valves

paulo57509

Search here: http://60degreev6.com/forum/forum.php

Consensus is yes, it is an interference engine. But you win some, you lose some. There are reports that it's the camshafts that break and not the chain.

I do have a high mileage '92 Lumina with a 3.1L with aluminum Gen-II heads.

I can't cite GM data because there probably isn't any. The reason you probably don't see documentation is because manufacturers and most timing component suppliers that publish interference vs. non-interference data are belt-centric and consider chains are lifetime components; no one ever puts timing chains on the preventative maintenance list in the owner's manual.

Even SBC's will smash valves when a chain lets go:

sofakingdom

iTrader: (1)

Stock SBCs are mostly NOT "interference" engines. However if you build one with dome pistons and a big cam, it can easily become one.

Stock BBCs on the other hand, are.

Yes I have had more than one of each that grenaded the cam gear while I was driving it, and have repaired MANY others: I know this from personal experience.

Neither of those things matters since the engine in question is neither.

I have not the vaguest foggiest dimmest remotest hint of a whiff of a glimpse of a clue about a 6-cyl in this regard however.

OrangeBird

iTrader: (1)

I have found nothing conclusive on the 6/60 site .....

I was told long ago when I ran into my first broken chain 2.8 that the 2.8 iron headed engines were not a problem bent valves wise in a stopped cam situation , and that the problems with this for the 6/60 began when they changed to an aluminum head during the change from it being a 2.8 to a 3.1 .

Now , I don't know if the above statement is right or not , but again I have over the years changed 2 broken chains on 2 different iron headed 2.8 engines , and neither had valve damage . This is why I was hoping (and i'm sure the OP was hoping as well) that someone would have had any "official" GM data as to exactly what the situation is with these engines .

OrangeBird

iTrader: (1)

And then there is this , from a Moderator in the V6 forum .

Still no GM tech sheets saying for certain and I don't have a spare engine around anymore to actually measure it for myself .