Timing Belt/Chain??

[billberry12]

Do these 3800 engines need to have a timing belt change at some point as preventative maintainence like the Japenses makes do?

Thanks,
BIll

[crash93ssei]

The camshaft is chain driven, but I don't know the change interval on the chain and gears, or if there even is one. I know that our '03 SSEi has 163,000 on the original chain and I am not even a little worried about it. I will probably change it sometime before 200,000 miles though just because.

[billberry12]

I thought so..just being sure...thanks.

[Bonneville92V688]

Yeah, no worries. Some earlier 3800s have went 300k+ without a timing chain replacement. And if you are curious, these engines are non-interference, like most pushrod engines are.

Most Japanese engines are OHC, which almost all of them are interference, which is why they strongly recommend replacing the belt when they say it's time.

[billberry12]

What do you mean by "these engines are non-interference"?

[crash93ssei]

That means that if the timing chain were to ever break, causing the camshaft to stop spinning, the pistons would not come up and slap the valves causing you to need headwork.

[Bonneville92V688]

Yeah, in a interference engine, if the timing belt/chain snaps, the valves will collide with the pistons, usually bending valves, cracking the head, damaging pistons, and scoring cylinder walls from pieces of the broken valves. It's not pretty.

[billberry12]

This is good news. One less thing to worry about.

[CMNTMXR57]

That means that if the timing chain were to ever break, causing the camshaft to stop spinning, the pistons would not come up and slap the valves causing you to need headwork.

Most modern, multi-cam engines do have a safety mechanism that once cam drive pressure is lost (generally by some tensioner, they automatically close all valves in order to save them from kissing the tops of the piston

[crash93ssei]

That means that if the timing chain were to ever break, causing the camshaft to stop spinning, the pistons would not come up and slap the valves causing you to need headwork.

Most modern, multi-cam engines do have a safety mechanism that once cam drive pressure is lost (generally by some tensioner, they automatically close all valves in order to save them from kissing the tops of the piston

First I have heard of that, it sure would make life a little nicer Do they use some type of solenoid or something?

[WhiteArrow3800]

Our 3800's have a chain tensioner as well. If the chain ever does stretch over time, the tensioner will keep it in check.

Though I have another theory about the tensioner, but that's another topic...

[CMNTMXR57]

That means that if the timing chain were to ever break, causing the camshaft to stop spinning, the pistons would not come up and slap the valves causing you to need headwork.

Most modern, multi-cam engines do have a safety mechanism that once cam drive pressure is lost (generally by some tensioner, they automatically close all valves in order to save them from kissing the tops of the piston

First I have heard of that, it sure would make life a little nicer Do they use some type of solenoid or something?

Most of them (GM as that's what I worked on) had a mechanical tensioner that when their was a break, let the cams free wheel to shut the valves. It's been awhile and I can't find any technical writeup on it.

[Jrs3800]

Lets be careful with what we are saying here..

Most of the 8.5 : 1 compression 3800's can survive if it jumps time, but thats no promise that you won't impact a valve if this were to happen..

The 93-95 Vin L engine is a 9.0 : 1 compression, so it has a shallower dish in the piston.. The Vin K and Vin 2 3800 NA is 9.4 : 1 compression and is almost a flat top piston..

Lets have an example... If you were running 80 Mph down the interstate and Poof the tensioner breaks and the chain jumps.... You would have a very good chance of impacting a valve..

The Nylon coated gears used in the 86-87 FWD LG3 3.8 was more than known for jumping time.. And in the worst cases valves were crushed, pistons and heads were destroyed..

These may be called non interference, but that doesn't mean it won't happen.. The 3800 designs have improved and this should not happen, but its not out of the realm of possibilities..

[crash93ssei]

I know about the tensioner, but won't at least one of the valves still be open somewhere? Is there any one spot on the cam that will allow all of the valves to be closed at the same time?