Two Conflicting Stories

[jpratt]

When a Buick 3.8 Turbo engine slips the timing chain can it damage the valves?

I have talked with several different shops, suppliers and one aftermarket engine manufacturer (Jasper) and gets two conflicting stories.

One side is that no it cannot damage the vavles at all an the other is that it almost definitely will damage the valves.

What is the truth to the matter? I would lean to believe you folks as you guys have these engines and have first hand experience.

 

[Adrian87]

Maybe they are thinking that the Buick 3.8 is a non-interference engine, which I do not believe it is. Usually on timing belt type import cars as far as I know...my .02

 

[FastRegalWE2]

not that I am an expert but.........if the engine is running when the timing chain breaks, it is more likely to damage the valves/pistons than if it isnt running at the time. Now, the chain usually breaks during start up as the stress on the chain is greater on one side at that time than when it is running. IE.....when you crank over the car the sudden jerk from all the rotating components weight on the chain and the worn nylon tippped cam gear teeth is usually when it breaks.

 

[jpratt]

That is excatly when mine let go. But some 'mechanics' have said that there more than enought room at the top of the piston for the valves to be open with the piston at TDC. Others have said that there is not room. That is Q

 

[kh440]

I've always been told that yes valve damage could occur. Course when my dear;y departed slung the chain somehow the #2 rod journal got chewed up.

 

[FastRegalWE2]

if it only jumped a tooth or 2 I DOUBT that any damage occurred

 

[MistaScott]

Even if you think you didn't bend any valves, do a leakdown test anyway to be sure. That will settle it.

These are interference engines -- you can bend valves when the timing chain breaks or slips. It is less likely if the chain breaks at idle or startup but still possible.

If the engine was running for any time after the chain slipped, you can be assured you bent valves as the timing was all screwed up.

 

[stickybones]

I busted my timing chain while running at about 70 mph. I bent at least one valve that I can remember.

 

[Dan Buick Man]

When I assembled my engine I lined up the wrong marks on the timing chain. Don't ask me how. The cam gear was off about 30 to 45 degrees. No major problems (besides it was firing through the intake and would not start.) Run a compression or leakdown test. Best way to tell.

 

[S10xGN]

I can tell you about my combination only (and I checked it myself while assembling it!). With #1 piston on TDC, head gasket installed and torqued properly, I could push down on both the intake and exhaust valves (very light pressure check springs!) and the valves would not contact the pistons until 0.485" was measured by the dial indicator on the valve retainer. This means that my engine is an interference type because my valve lift is 0.520". If I were running a stock cam, I don't believe there'd be any problem (on my engine)...

 

[OneLethal87GN]

I guess I was lucky but my timing chain was missing quite a few teeth and slipped several times and even had one break while my mechanic was testing it out. With all that said I never ended up with a bent valve. My engine was bone stock at the time though.

 

[scottyb]

My chain tensioner broke in March as I started the car one morning. The chain just free-wheeled over what was left of the plastic cam gear. It made a zipping noise. I did not do a leak-down, but the compression test was good and after installing the new gear and chain set, the car runs better than ever. Two weeks later I did the valve springs and found one bent pushrod.

I talked to a local Buick guy and he said that they are interference engines, but out of about 4 broken chain sets he had no bent valves.

 

[2QUIK6]

When changing the valve springs, if piston was at TDC, I could depress the value/spring assembly and touch the piston, thats how I ended up dislodging a few of the retainers because the valve would continue to depress even with the cyclinders pressurized with and air compressor when depressing the springs to release the retainers.