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  • Question : Interference Motor?

    Settle something for me , please? the 2.8/3.1/3100 are NOT interference motors. Correct? Someone doesn't want to believe me, and I TRIED to explain to him, that the only GM motors I'm aware of being interference motors are OHC , not OHV. I even called my GM dealership and spoke with a tech and the parts guy about it.
    Just wanted to see what some of you 60* guys thought.

  • #2
    They ARE interference motors. A common destruction of a 3X00 motor is a snapped cam causing the pistons to take out the valves. It all starts with the LIM gasket going bad and the valves hitting the piston.

    Pretty much all new GM engines are interference motors including the diesel ones.
    1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
    1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
    Because... I am, CANADIAN

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    • #3
      Thank you betterthanyou

      And why should I believe something that is wrong?

      I've built 3 motors now of the OHV era, and all of em if the cam chain is not on you can not turn over the motor unless the rockers are removed.

      I also work on a GM 350 in a race car, SAME principal and also an Interference Motor.
      Last edited by 3400-95-Modified; 07-07-2008, 05:47 PM.

      Got Lope?
      3500 Build, Comp XFI Cam 218/230 .050 dur .570/.568 lift 113LSA
      Fully Balanced, Ported, 3 Angle Valve Job, 65mm TCE TB, S&S Headers.
      Stage-1 Raybestos/Alto 4t60e-HD, EP LSD, 3.69FDR
      12.61@105 Epping NH Oct 2015 Nitrous 100shot (melted plugs) 13.58@98.8 N/A 3200LBS

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      • #4
        Sadly, they are interference. You'd think with the MPFI engines having 8.8:1 Compression it would not be.
        Lifting my front wheels, one jack at a time.

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        • #5
          Ok, someone besides Jon, explain this to me then please. I used to be a GM mechanic, and this is the first time I'm hearing this. I even called and talked to a few GM employees today ( a tech, and a parts guy,BOTH in the field a long time) at length. BOTH said I was absolutely correct in thinking the only interference motors GM ever put out were the OHC ones, and generally they used a belt with exceptions like the Quad which used a timing chain.

          Comment


          • #6




            When the T-Chain breaks and the crank is still rotation... That will happen. I would have been grateful if that didnt happen when the chain snapped.
            Lifting my front wheels, one jack at a time.

            Comment


            • #7
              I dont know of any GM motors that ARENT interference motors, i know my 2.2 ohv in my cavalier is and so is the 60* v6 like others have said.

              I've only ever seen one motor that wasnt and interference motor and it was a 2.2/2.5 in the dodges in the late 80's early 90's
              Mr_Efficiency

              90 Grand prix - Lawn ornament
              Black, 3.1, 5 speed
              Future holds: Striped and then scrap yard

              97 Cavalier - Stock car
              Red/Black, 2.2 OHV, 5 speed, fully tubed bumper to bumper, 6 point cage with halo, fuel cell, race seat, 5 pt harness.... a race car
              Future holds: Just more trophies

              New project on the way: 88 S10 reg cab, short box, 5 speed.
              Future holds: Built 2.8 hybrid, Stealthy flat black, a drop until i have no more ugly wheel gap

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              • #8
                If a motor has low compression and a low lift cam you may end up without interference. But it is usually not the case. Combustion chambers are small and valves are close to the deck and lift is almost always above .400 inch. All this helps promote breathing, swirl in the chamber and a descent compression ratio. Interferance or not really has nothing to do with where the cam sits. In either engine design the clearances between the pistons and the valves during operation and not much different.
                1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
                1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
                Because... I am, CANADIAN

                Comment


                • #9
                  But , you would normally only worry about smashed valves in say, a 3.4 OHC, or a 2.3 Quad, right?

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                  • #10
                    Originally posted by Mr_Efficiency View Post
                    I dont know of any GM motors that ARENT interference motors, i know my 2.2 ohv in my cavalier is and so is the 60* v6 like others have said.

                    I've only ever seen one motor that wasnt and interference motor and it was a 2.2/2.5 in the dodges in the late 80's early 90's
                    The Iron Dukes found in the s10's are non interference.
                    Lifting my front wheels, one jack at a time.

                    Comment


                    • #11
                      Originally posted by SuzukiGhostRider View Post
                      But , you would normally only worry about smashed valves in say, a 3.4 OHC, or a 2.3 Quad, right?
                      Of course. Typically OHC engine see a lot more timing belt/chain breakage due to the fact the thing is so damn long. When it stretches just a bit they start to slap around. Most do have tensioners but they only work to a point. People usually forget about regular maintenance and just let the thing explode. Look at a Honda for instance. They recommend changing the belt ever 100,000kms. But a 60 degree V6 you may never change the chain or perhaps do it because the front cover gasket is leaking. My Trooper motor has 280,000kms on it and I still feel no need to dive into it to change the chain out. I will do it when I rebuild the motor and make it a 3.1L.
                      1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
                      1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
                      Because... I am, CANADIAN

                      Comment


                      • #12
                        Bottom line a GM 3100, 3400 3500 and 2.8's and 3.1's are still all interference... It doesn't matter which one you would worry about more...
                        Attached Files

                        Got Lope?
                        3500 Build, Comp XFI Cam 218/230 .050 dur .570/.568 lift 113LSA
                        Fully Balanced, Ported, 3 Angle Valve Job, 65mm TCE TB, S&S Headers.
                        Stage-1 Raybestos/Alto 4t60e-HD, EP LSD, 3.69FDR
                        12.61@105 Epping NH Oct 2015 Nitrous 100shot (melted plugs) 13.58@98.8 N/A 3200LBS

                        Comment


                        • #13
                          Originally posted by 1988GTU View Post
                          The Iron Dukes found in the s10's are non interference.
                          And don't forget, they were also in Citations! Doesn't matter that they are non-interference because there is no timing chain in those engines, the cam is geared off the crank. Beautiful setup, actually.

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                          • #14
                            Yup the duke has got to be one of the most reliable engines out there. Basic and built strong. Mercruiser used the engine design with its own variations to do marine duty as well.
                            1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
                            1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
                            Because... I am, CANADIAN

                            Comment


                            • #15
                              I was worried about if our motors are like that or not, because I have wondered that if I hypothetically floated the valves at top end or redline, would they hit? I figured yes they are interference mainly because there aren't any valve reliefs in the pistons. My roommate accidently hit his rev limiter once in his bmw, floated all exhaust valves and bent them. Cause: weak valve springs. I'm just worried that with 140,000 miles on my 3100, if I hit above 5600 rpm. Will there be damage?
                              Eric

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