what years were interfernece engines?

[craftsman_454]

hey,
i've got a 91 lumina, just wanted to know if my engine is an interfernece engine, i heard only some early 90's engine are interference.

[dohcfiend]

RE: what years were interfernece engines?

from what i have heard only 96-97 were interference motors.

[SappySE107]

RE: what years were interfernece engines?

Yup, and we aren't even certain those are interference. Its commonly accepted that if your belt breaks at high RPM, there is a chance of it hitting pistons since it has happened before. However, without any stretch or wear, there shouldn't be any valves hitting the pistons at TDC and max valve lift.

[craftsman_454]

hhmmmm so your saying there is a possibility of the valves making contact with the pistons if the belt breaks at high rpm... as far as iim concerned thats interference. did the compression ratios vary in the early 90's???

[SappySE107]

Well, its not interference as its not 100% that they are gonna make contact. Valve float may be another factor, im not really sure. The only time the belt gave out on me was in a friends car around 5k RPM and nothing hit. You can have the valves at TDC and spin the crank over without it hitting as well. Like I said, rod stretch and bearing wear are probably the reasons for the instances where it did hit.

The 5 speeds had .25 higher compression from slightly less valve cut outs in the pistons.

[dohcfiend]

from memory again 91-94 auto's are 9.25:1 manuals are 9.5:1
94-95 not exaxtly sure but i think 9.25:1
96-97 are 9.7:1

[SappySE107]

manual was 91-93 only. 91-95 are 9.25:1

[series8217]

With my heads decked over .018 past minimum factory cast thickness my valves still dont hit the pistons when I spin them all the way around. These things have plenty of clearance I guess.