Is the DOHC 3.4 an interference engine

[Faust]

I am looking at a Grand AM DOHC 3.4 that doesn't run. If the belt is gone am I in serious trouble?

[RidgeRunner]

I assume you mean Grand Prix. What year is the car?

[brian89gp]

96-97 yes. 91-95 no but it has been known to happen in rare cases.

[dykz34]

Odds are higher that it became an interference motor if they belt broke at 6k.

[Faust]

I assume you mean Grand Prix. What year is the car?

It is a '93. 5 speed.

[Anonymous]

I have a 92 5-speed and it doesn't interfere. I am positive it doesn't......

[VerbotenZ34]

Not if it's prepared correctly. Just cover it in some tin foil or other reflective material, and the waves should just bounce--ooohhhh, you mean MECHANICAL INTERFERENCE.
Sorry, I thought you were inquiring about electromagnetic interference. (j/k)

Verboten LOL

[Lyle's GTP]

Yah, if you throw a belt @ 6000RPM, when you do have some valve float. You will definatily bust up a few valves. It has happened.

Lyle

[pontiac92gp]

Im lookin to rebuild the 3.4LTDC .. What shouldnt I change to keep it non-interference?

[Lyle's GTP]

Cams, lifters, pistons and deck height are the only thing you could change, that could effect this. Depends what you want to do. But throwing a timing belt is very rare if you keep a fresh one on. I wouldn't worry about it. Improper maintenace will cause any engine to fail. The 3.4l DOHC has a couple more things to watch for that's all.

Lyle

[SappySE107]

valve float! no no no, i hope not! The rods stretch at high RPM, and that is why it is possible for the piston to hit the valves if they are at full open when the piston is at TDC and things stretch a bit too much.

[Lyle's GTP]

I've heard of valve float in these engines, guys are putting .030 shims in to add more spring tension to prevent this. Could be wrong, but I've heard it's a problem with high RPM engines.

Lyle

[jmgtp]

Ive had no problems with valve float at engine speeds over 7000 rpm.

My Tbelt tensioner broke at 4k rpm and everything went out of time. No damage done though.

[SappySE107]

Supposedly the 96+ engines have weaker springs. I have some .060 shims to put in with my 96 springs this summer. That will bring them up to 91-95 standards (5 more pounds at the seat, 5 less at full lift). I found a place that makes the perfect sized shims but am waiting on a price. I probably have valve float but only because I have the 96 springs and go to 7150.

[jmgtp]

GM did some backwards engineering on that one then. They made the 96 engine to develop power in the higher range then put weaker springs in it?! I suppose they never imagined anyone would be revving it beyond 6500 since it only came mated to an auto.