chevy 350 interference heads?

[mikehaugen]

I got a '97 suburban with the 5.7 vortec. The timing chain cover is leaking, and I figured with almost 200k, I would change the timing set as well while I am in there. I don't believe it is an "interference" motor, but thought I would check just so I know ahead of time since I am sure that somewhere in this process something will get moved and I don't want to damage valves. Or any other advice is appreciated.

 

[94BULLITT]

Yes it is a interference engine.

 

[Dmace]

Technically they are not an interference engine. Lose a chain at high RPMs and the valves could float and make contact but at low RPMs they will not touch.

According to the manual, setting the timing requires a scan tool:
Setting Timing
Camshaft ****** Offset Test
The ignition timing cannot be adjusted. The distributor may need adjusting to prevent crossfire. To insure proper alignment of the distributor, perform the following:

With the ignition OFF, install a scan tool to the DLC.
Start the engine and bring to normal operating temperature.

Important
Cam ****** Offset reading will not be accurate below 1000 RPM

Increase engine speed to 1000 RPM.
Monitor the Cam ****** Offset.
If the Cam ****** indicates a value of 0° ± 2°, the distributor is properly adjusted.
If the Cam ****** does not indicate 0° ± 2°, the distributor must be adjusted.

Adjusting Camshaft ****** Offset
With the engine OFF, slightly loosen the distributor hold down bolt.
Important: Cam ****** Offset reading will not be accurate below 1000 RPM


Start the engine and raise engine speed to 1000 RPM.
Using a scan tool monitor Cam ****** Offset.
Rotate the distributor as follows:
To compensate for a negative reading, rotate the distributor in the counterclockwise direction.
To compensate for a positive reading, rotate the distributor in the clockwise direction.
Repeat step 4 until 0° ±2° is obtained.
Turn the ignition OFF.
Tighten the distributor hold-down bolt to 3N·m(25 lb. ft.).
Start the engine, raise engine speed to 1000 RPM and recheck Camshaft ****** Offset.

But Ignition timing is easily set at the distributor by finding TDC in cylinder 1 then lining up the distributor mark with #8.

 

[tcartwri]

Technically they are not an interference engine. Lose a chain at high RPMs and the valves could float and make contact but at low RPMs they will not touch.

This is not correct. They are absolutely an interference engine.

Do not rotate the crank when the chain is off. You should pull the plugs so that there is no residual compression, although unlikely. Bring the motor to TDC on #1 before you pull the chain off. You may have to rock the crank back and forth a few degrees to get the sprocket and chain back on. Put the balancer in the oven at 250 for 15 minutes before you try to put it back on. Take it straight from the oven ( disregard wife ) , lube the snout with oil, and slide it on as far as you can before it sticks. Use the balance bolt with a stack of lubed washers to pull it on the rest of the way. Do not hammer the blancer on. Do not apply too much torque to the balancer bolt, as it WILL strip the crank snout and ruin your day.

 

[firefighter jim]

This is not correct. They are absolutely an interference engine.

Do not rotate the crank when the chain is off. You should pull the plugs so that there is no residual compression, although unlikely. Bring the motor to TDC on #1 before you pull the chain off. You may have to rock the crank back and forth a few degrees to get the sprocket and chain back on. Put the balancer in the oven at 250 for 15 minutes before you try to put it back on. Take it straight from the oven ( disregard wife ) , lube the snout with oil, and slide it on as far as you can before it sticks. Use the balance bolt with a stack of lubed washers to pull it on the rest of the way. Do not hammer the blancer on. Do not apply too much torque to the balancer bolt, as it WILL strip the crank snout and ruin your day.

Ditto................interference engine

 

[Diamondpilot]

If the chain is not broken I would just make reference marks, take old off, install new.

Chris

 

[mikehaugen]

thanks for the responses guys, I was finding conflicting stories when I did a google search.

 

[brokenot]

So who do you believe, and what proof have they shown you? Googling anything from "Interference engine list" to "Vortec 5.7 valve interference" to "Vortec 350 valve-to-piston clearance" shows nothing....if what we're looking for is whether or not a stock 5.7 Vortec is an interference engine or not.

There are thousands of posts about engines that have over-revved and had the pistons and valves kiss each other, or carboned-up guides causing valves to hang open and hit the pistons, or improper combinations of heads/pistons used together, or modified engines with higher-lift camshafts and whatnot causing interference, but none of those things constitutes what is defined as being an "interference engine".

I've seen 4.3 Vortecs assembled with the camshafts out of time, and no....the pistons and valves did not contact each other. The 4.3 is essentially a 5.7 minus two cylinders, so damage should have occurred if it were indeed an interference engine.

Those that have said the Vortecs are interference engines, (in stock form), have yet to show where their information is coming from. Anyone got a link to share or a scan of a service manual?

 

[mikehaugen]

I would say that it is just safer to assume that it is and treat it accordingly. If they had said "it is not an interference engine, it doesn't matter what you do" then I would be more skeptical. It could be that I will pull the cover off and the chain slack will be within the tolerance and in that case I may not even change it, but I doubt it. Reading the responses makes me think that I will just line up the timing marks for installation before removal and then just not move them when I put the new ones on, I just know that sometimes things don't go the way we plan. BTW, I do have a GM service manual and it doesn't include any cautions about rotating the crank with the timing chain off, but still thought it was a good thing to ask.

But yes, I know what you are saying about relying people you don't know for information. There isn't anyway of knowing if they are right or not, but then again, I have found "professional" mechanics that don't know what they are talking about so there is really nobody you can trust. And aside from me being cheap, is a big part of the reason that I do my own work on things. It is how we learn, and with enough research is really the only way you know that it was done right.

 

[tcartwri]

The term Vortec refers simply to the shape of the combustion chamber. It is still the same basic motor that came out in 55. A stock motor can have the cam timing out by +- 20 deg and still not get contact. Increase the duration of the cam and things get critical. Lift actually has little to do with it. There are dozens if not hundreds of rebuilder manuals on the SBC alone. Ford another hundred if you're inclined to look it up. Myself, I've been racing them for more than 30 years.

Stock cams have valve lift on the order of .380~.400". Running clearance is ~ .100". Break the chain or rotate the motor without a chain and you have at minimum .250" of intereference.

 

[timswi]

If the chain is not broken I would just make reference marks, take old off, install new.

Chris

That's what I've done..If the chain is still in one piece the computer will adapt the timing, it has thus far..Why would anyone move the crank or cam with the timing set removed?

 

[brokenot]

There are quite a few posts out there on the 'net from people that have, (or want to), install higher-lift camshafts in Vortec engines and have experienced issues with valve spring bind or interference with the pushrod holes, or valve springs or retainers hitting the valve stem seals or guides at full lift. Some have also put Vortec heads on older blocks, (or vice-versa?), and have had issues with the valve clearance to the bore in the block. A lot of them have come to the conclusion as a result, that the Vortec is indeed an "interference engine". But that isn't what the term "interference engine" refers to.

Interference engine means that in stock condition, operating under the conditions it's designed to operate in, the valves will hit the pistons if the camshaft gets out of time. Several internet posters have claimed that Vortecs are indeed interference engines because their engine bent its valves when their clutch let go on the starting line and their tachometer needle ventured into territory it doesn't belong in. If that's the definition everyone agrees to go with, we'll have to expand the list of interference engines by quite a bit.

Here's a link to a Vortec "beehive" valve spring kit. A few guys that have installed these have posted that they cured the "interference engine" issue, (that they don't really have as far as I know), with their Vortecs.

Valve Spring Upgrade - Beehive Valvesprings for the Vortec V8 - Car Craft Magazine

The jury is still out as far as I'm concerned. Until I measure one myself or see it in a shop manual, I don't think the Vortecs belong on the interference engine list. Not too far off-topic, I got one of the "shop tips" emails at work from Foley Engines a while back, and it said 2.3 and 2.5 Fords are interference engines, and they aren't. They went on to say that the Deutz diesels with timing belts are too....they did get that one right.

Why would anyone move the crank or cam with the timing set removed?

It's done all the time to get things lined back up if a chain jumps or a belt breaks. A person needs to be careful and know what they're doing though....

 

[tcartwri]

You need to get your hands dirty and stop reading so much. This is a rediculous discussion.

 

[brokenot]

You need to get your hands dirty and stop reading so much. This is a rediculous discussion.

Interesting comment, it kind of sounds like you're not so convinced yourself.

And....ridiculous contains no "e". That aside, why is attempting to answer, (or find answers), for someone's question ridiculous?

Stock Vortec. Interference engine or not? Post proof.

Lastly, my hands are dirty on a daily basis.

 

[puckgrinder85]

Line the timing marks up, remove and reinstall, nothing more really needs to be said about it unless you plan on rotating something for whatever reason which it doesnt sound like you have to.

 

[dodge man]

I don't know the technical defintion of a interference engine, but I always thought of it meaning if the timing chain broke, would the valves hit a piston. Knowing how modern engines work, I'd be shocked if it wasn't, but you never know kunless you get the specs or talk to someone that knows what they are talking about.

 

[Diamondpilot]

I still think everyone is making this harder then it needs to be. Like i said earlier and others have too, just mark everything with reference marks, remove old one, and install new.

Chris

 

[mikehaugen]

well geez, this wasn't supposed to turn into a p*ssing match. The only reason I ask is because I know me sometimes and I could see myself possibly rotating the crank or something unintentionally and was just curious if it would be a problem if it did happen. As stated earlier, I will just treat it as if rotating the engine without chain will cause engine to explode immediately and lightning will strike my garage, no harm in being overly cautious. Thanks for the replies.

 

[Diamondpilot]

well geez, this wasn't supposed to turn into a p*ssing match. The only reason I ask is because I know me sometimes and I could see myself possibly rotating the crank or something unintentionally and was just curious if it would be a problem if it did happen. As stated earlier, I will just treat it as if rotating the engine without chain will cause engine to explode immediately and lightning will strike my garage, no harm in being overly cautious. Thanks for the replies.

I am sorry if I came off negative and I will apologize for anyone else also. If the chain or belt has not broken or skipped a tooth and is otherwise running perfect as you seem to suggest I would just do as we said and with reference marks made swap the parts.

Chris

 

[brokenot]

My apologies as well. I'm genuinely interested in a definitive answer. There are interference engine lists posted on the 'net by timing components manufacturers, and the Vortec isn't among them. Additionally, I saw a co-worker try and start a Vortec 4.3 for quite a while...before ending his experimenting and lining up the marks properly. No damage at all, and from the amount of time he spent fiddling with it, the crank and cam were probably lined up a few different ways. (No, I don't know why.) Then there are all of the different versions of the story you can read on other forums. One guy actually said it was an interference engine for sure, because his bent an intake valve. The kicker is, he had the truck back on the road after pulling the head and replacing the bent valve....and that's all. Nothing was done with the cam or crank positions whatsoever.....