highmileage driver Posted June 20, 2003 Report Share Posted June 20, 2003 I own a 1995 Chevy Monte Carlo Z34, with 188K miles on the car, and supposedly a 60K mile rebuilt motor). I unfortunately let the timing belt break on me 2 weeks before I was scheduling to replace it. Now I am told that I have a 50% chance on whether the pistons made contact with the valves. So I am forging ahead and replacing the belt without checking the valves for damage. Not sure on timing procedure of the DOHC 3.4L engine after replacing a broken timing belt. I have the crankshaft pulley at TDC on the #1 piston, the new belt is in place, and the "special" GM clamping brackets are in place on both the front and rear cam banks. My question is basically this. My "Haynes" manual is telling me that "correct" cam timing is achieved when the rear bank cams are "flats" down (the flat spot on the camshaft that the special tool is suppose to hold unto) and the front bank cams are "flats" up. In contrast to this, my local mechanic is telling me the both the front and rear cam banks are "in time" with each other when they are both being down down with the special GM clamping tool (while the crankpulley is at TDC on the #1 piston). Obviously dont want to mess up my timing on the motor and end up with an empty wallet (not much in there to begin with). If anyone can help me out I would very much appreciate it. Thanks! Highmileage Driver Quote Link to comment Share on other sites More sharing options...
Redfox340 Posted June 20, 2003 Report Share Posted June 20, 2003 Well, you could be in for a surpise after start-up if the pistions made contact with the vavle-train. I know that the 1994+ DOHC's were "Interferring" motors, so I wish you the best. Second, if you having trouble re-timing the DOHC, check 60degreeV6.com; they've got the full procedure in English. Welcome aboard and again, wish you the best on you Monte Carlo. EDIT: Exact link to Secondary Timing Belt: http://www.60degreev6.com/index.php?p=pages&pid=255 - Erik Quote Link to comment Share on other sites More sharing options...
SmokesGTP Posted June 21, 2003 Report Share Posted June 21, 2003 I was under the impression 1994's were not interference? Quote Link to comment Share on other sites More sharing options...
Redfox340 Posted June 21, 2003 Report Share Posted June 21, 2003 I was under the impression 1994's were not interference? Not to what I know is true. Perhaps some of the members can share some light on the topic. 1991 - 1993(?) were "Non Interfering" 1994 - 1996+ were "Interfering" However I've heard of a Non Interfering have internal damage due to a snaped belt. It happen on EFI-Street.com and a rare occurance. - Erik Quote Link to comment Share on other sites More sharing options...
SmokesGTP Posted June 21, 2003 Report Share Posted June 21, 2003 Yeah from all I have read its rare unless you snap it at redline or something. I remember reading that 1995-1996 were the only definite interfering. Hopefully someone knows this for sure. Quote Link to comment Share on other sites More sharing options...
chronic139 Posted June 21, 2003 Report Share Posted June 21, 2003 96 motors are the only real "different" motors from the rest, but i thought that none were interferance. Quote Link to comment Share on other sites More sharing options...
GnatGoSplat Posted June 24, 2003 Report Share Posted June 24, 2003 91-93 are the same. 94-95 are the same. 96-97 are the same. I thought the 94-95 were more similar to the 91-93 and 96-97 were the only ones that were real different. Quote Link to comment Share on other sites More sharing options...
lukee1982 Posted June 24, 2003 Report Share Posted June 24, 2003 i have heard that only 96 is an interference motor however every motor has a possibility if the belt snaps at high rpms most likly you are safe i will probably be seeling the timing gm timing video that i have fairly soon on ebay may keep it till i do the belt. I have a friend bbender85 snapped his at over 5500 and still didn't hit his valves. replace everything as stated and buy your parts from gmpartsdirect.com it will save you $ Quote Link to comment Share on other sites More sharing options...
Baddflash Posted June 25, 2003 Report Share Posted June 25, 2003 The early DOHC are interferance as are all of them as far as I know. If I were you I would pull your heards and check the valves as your chances of survival are slim to none but it totally depends on what you were doing at the time of breakage. I'd really check the heads first before going through all the work of retiming and putting it back together just to start it and cause more damage. Money might be tight but it'll cost you a lot more if they didn't survive and you start that thing up. Just MHO though. Quote Link to comment Share on other sites More sharing options...
Redfox340 Posted June 25, 2003 Report Share Posted June 25, 2003 The early DOHC are interferance as are all of them as far as I know. If I were you I would pull your heards and check the valves as your chances of survival are slim to none but it totally depends on what you were doing at the time of breakage. I'd really check the heads first before going through all the work of retiming and putting it back together just to start it and cause more damage. Money might be tight but it'll cost you a lot more if they didn't survive and you start that thing up. Just MHO though. Mine snaped after down-shifting to 3rd gear @ 5500 RPM's and no internal damamge on my 1992. I freaked out just the same once I located the problem, but talk to a close friend in the Chevrolet service department at a local dealer and siad I've got really nothing to worry since the valves closed to the "normal position" and being a NON - Interfering motor. That why my DOHC (sold) is still being driven today. - Erik Quote Link to comment Share on other sites More sharing options...
Baddflash Posted June 25, 2003 Report Share Posted June 25, 2003 I had to replace engine in a 92' Cutlass because the belt snapped (pulley bearing seized) and the valves got beat into the heads. If non-interferance motor how did the heads gets smoked?????????? Doesn't seem like anyone know for sure?? Just the same I had one let go on me and no damage???? Quote Link to comment Share on other sites More sharing options...
GnatGoSplat Posted June 25, 2003 Report Share Posted June 25, 2003 Ya know, I just remembered I had a friend that owned a 95 Monte Carlo Z34 and his belt broke at 30k miles leaving him stranded. The car just died while he was cruising. Turned out no damage was caused to the valves. I think it has a lot to do with how close the tolerances are. The pistons are dished to provide valve clearance, but I think this clearance is very, very small. Quote Link to comment Share on other sites More sharing options...
Redfox340 Posted June 25, 2003 Report Share Posted June 25, 2003 If non-interferance motor how did the heads gets smoked?????????? However I've heard of a Non Interfering have internal damage due to a snaped belt. It happen on EFI-Street.com and a rare occurance. You didn't read what I posted huh? There's been the unfortunate cases of having valve trouble... but overall it's minimal to all the times a DOHC has craped a belt. - Erik Quote Link to comment Share on other sites More sharing options...
brian89gp Posted June 25, 2003 Report Share Posted June 25, 2003 91-95 are non interference, 96-97 are interference. If the belt breaks at high rpm on a 91-95 motor there is a very slight possibility of ramming a valve into a piston but its unlikely. The damage is done to the piston and the misfortunate valve, if it is hit right the bent valve can be jammed back into the valve guide fucking that up in the process. It is called THE timing belt, there is no secondary timing belt. There is a timing belt, timing chain, and serpentine belt. 91-95 motors for all general purposes are basically the same, the only changes to it was sensors and provisions to mount those sensors. The 94-95 got: -different front cam carrier to house the cam sensor -front intake cam with cam sensor teeth on it -different front timing chain cover and harmonic balancer to accomidate the 24x crank sensor -the crank pulley is slightly different due to the different harmonic balancers -MAF instead of MAP, same plenum but the plastic end plug is different -different routing of vacuum lines, PVC line, and cam carrier breather lines -heated o2 sensor -alternator with 2 internal cooling fans vs the 91-93's 1 external fan -different ECM to handle SFI -no oil cooler I think thats all. For all who care the 91-95 can be considered 1 engine. 96-97 got redesigned pistons, heads, cams, cam carriers, intake, and exhaust. 91-95 pistons are flat-top pistons with valve reliefs cut in them, 96-97 have domed pistons. Quote Link to comment Share on other sites More sharing options...
SmokesGTP Posted June 28, 2003 Report Share Posted June 28, 2003 Thank god somebody knows what they are talking about, thank you. So basically GM backtracked and decided it would be nice to turn a non- interference engine into an interference motor for 5 more horses? Quote Link to comment Share on other sites More sharing options...
SleeperRed90TGp Posted June 28, 2003 Report Share Posted June 28, 2003 When you get it back together take a compression test. It will tell you the whole story. Good luck. Quote Link to comment Share on other sites More sharing options...
bigbadrat Posted July 9, 2003 Report Share Posted July 9, 2003 ok i have read the things to do on replacing the belt.i have the info at work to set it,but how do you turn the motor 360 degrees with the front cams still locked.i tryed it and am afraid that i will mess up the belt.help me please before i put this car back in the water. Quote Link to comment Share on other sites More sharing options...
93Luminanewb Posted July 9, 2003 Report Share Posted July 9, 2003 I have an opportunity to buy a 92 Z34 (5 speed) with the 3.4 in it for $400. The owner said his wife was driving it and the belt tore apart, lost some teeth and messed up the timing (but still ran) and she drove for less than a mile with the car running like crap. He said that the valves were bent because the car "sounded bad" after he put a new belt on. My question is, are the valves really bent or is there a chance that he messed up the timing? Any replies would be great, sorry for hijacking the thread :oops: Quote Link to comment Share on other sites More sharing options...
Vegeta Posted July 10, 2003 Report Share Posted July 10, 2003 Most likely screwed the timing up when the new belt was put on. I would chance it for 400 bucks, cause you can sell the parts for more or get a new head cheap anyway. the 96 pistons are dished as well, and those engines could be non interference just like the older engines. I haven't seen any information stating it was on a reputable source. For all I know that was said on the same site that talked about sodium filled valves and 280 hp dreams. Anyway, 91-95 are definetly not interference. Quote Link to comment Share on other sites More sharing options...
93Luminanewb Posted July 10, 2003 Report Share Posted July 10, 2003 Thanks for the reply, that's what I was thinking, I just needed a bit of reassurance. By the end of next week i should have 2 W bodies. Yay Quote Link to comment Share on other sites More sharing options...
lukee1982 Posted July 10, 2003 Report Share Posted July 10, 2003 I have an opportunity to buy a 92 Z34 (5 speed) with the 3.4 in it for $400. The owner said his wife was driving it and the belt tore apart, lost some teeth and messed up the timing (but still ran) and she drove for less than a mile with the car running like crap. He said that the valves were bent because the car "sounded bad" after he put a new belt on. My question is, are the valves really bent or is there a chance that he messed up the timing? Any replies would be great, sorry for hijacking the thread :oops: well depending on what he replaced it could just be the tensioner jamming making the belt more likly to break. also there is a posibility that the timing is off due to the timing chain having skipped a tooth(not very likly but possible Quote Link to comment Share on other sites More sharing options...
JS91Z34 Posted July 12, 2003 Report Share Posted July 12, 2003 Yeah from all I have read its rare unless you snap it at redline or something. I remember reading that 1995-1996 were the only definite interfering. Hopefully someone knows this for sure. Yes 95-96 3.4L were considered the only interference motors. Non-interfrence motors can have damage to valve train upon timing belt failure. The term non-interfrence motor is just another way of stating that piston to valve contact would be minimal or unlikely. Lets face it for those of you with the non-interference motors don't think your out of danger. For me personally when my belt breaks, that will be the time I buy a new motor. My car sees the 7k mark more than it sees idle! Quote Link to comment Share on other sites More sharing options...
Vegeta Posted July 12, 2003 Report Share Posted July 12, 2003 95 is the same as 94. I think you meant 96-97. Quote Link to comment Share on other sites More sharing options...
JS91Z34 Posted July 12, 2003 Report Share Posted July 12, 2003 no Quote Link to comment Share on other sites More sharing options...
GnatGoSplat Posted July 12, 2003 Report Share Posted July 12, 2003 no Vegeta is correct. If that's not what you meant, then you're wrong. Quote Link to comment Share on other sites More sharing options...
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