First off I should mention that this is just a general question about the 96+ 3.4 DOHC and not about Fieros. I am not a fiero owner but I do realize that the dohc is a fairly popular engine to swap into Fieros and that is why I have come here in hopes to find some information from your experiences. If this is not okay, then please Moderator, delete this message. I have posted this on 60degreeV6.com but it seems there are no memebers there familiar with the 96+ dohc, myself included as I own a 91 model. That said:
Since the 96+ DOHC engines are interference engines, when installing a new timing belt if the crank is turned but the cams are not spinning (say if you have installed the new belt but have not locked the cam pulleys down so the crank and belt spin but the cam pullies are spinning freely on the camshafts - and you are rotating everything to seat the belt before timing the cams) wouldnt the valves strike the pistons? If so at such a low speed and force would this be damaging? If the cams flats are all facing upward and lock down tools installed would the valves be situated in such a way that they would not be struck by the pistons? Would this be the correct and only way to spin the crankshaft without the camshafts spinning (in time with the crank) and not cause damage? Ive done my 91 belt twice (flirted with 13* retard on the exhaust cams before I opted to go to -16*) so I know the procedure, but valves striking pistons was not an issue as pre 96 dohcs are non interference motors. I'll replacing the Tbelt on a 96 engine in the coming weeks and was wondering if the valve clearance would be an issue and if there was a certain sequence in doing this in order for it to be ok. Sequence meaning if cam flats should be installed before spinning the engine to seat the belt but with the cam pullies spinning freely on the camshafts (i.e. before timing them)? Anything else I should be aware of regarding timing a 96. My only other concern is if my existing specialty tools from the 91 will fit the 96, those tools being the cam flat hold downs and cam gear holder (as I understand I wont be needing the cam gear puller for the 96 with the redesigned lock rings).
thank you all,
-John
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04:11 PM
PFF
System Bot
normsf Member
Posts: 1682 From: mishawaka, In Registered: Oct 2003
Point 1 - The 3.4L DOHC/TDC motors are supposed to be "Free Spin" meaning the valves do NOT collide under any circumstance. As oppsed to a "zero tolerance" motor where they do. I got the term "Free Spin" from my 1991 Grand Prix GTP 3.4L TDC Engine Manual.
Point 2 - Timing procedure is to lock both sets of cams, flat side up with the locking tool. Turn piston 1 to Top Dead Center. Install the timing belt. Loosen the cam pulleys on the right side of the motor and remove the cam hold down tool from the left. Rotate the crank one complete rotation (180 degrees on the cams without the hold down tool). Now lock down the cam pulleys on the right bank and remove the hold down tool.
Everything should be timed now
At least that's the way I understand it working. If NOT, let me know
Best,
DKOV -
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05:46 PM
ryan.hess Member
Posts: 20784 From: Orlando, FL Registered: Dec 2002
Point 1 - The 3.4L DOHC/TDC motors are supposed to be "Free Spin" meaning the valves do NOT collide under any circumstance. As oppsed to a "zero tolerance" motor where they do. I got the term "Free Spin" from my 1991 Grand Prix GTP 3.4L TDC Engine Manual.
Point 2 - Timing procedure is to lock both sets of cams, flat side up with the locking tool. Turn piston 1 to Top Dead Center. Install the timing belt. Loosen the cam pulleys on the right side of the motor and remove the cam hold down tool from the left. Rotate the crank one complete rotation (180 degrees on the cams without the hold down tool). Now lock down the cam pulleys on the right bank and remove the hold down tool.
Everything should be timed now
To correct point 1... ... The earlier 91-93 or "Twin dual cam" engines were not interference, and you could do whatever you wanted with them without having to worry about valves. The 94(?)-96 "DOHC" were interference engines.
I know how to time the engine. Done it twice before. Just not on a 96. 96+ dohc motors are in fact interference motors, that is why I am concerned that while I spin the crank to seat the belt or bring it to TDC if the valves may have contact. Every write up I've seen concerns 91-95 motors which are non interference. Although I havent checked the links posted above, but I will do so now. Thanks all!
edit: no luck with finding info for the 96 engine on those sites Can anyone verify wether or not I should be concerned with striking a valve with a piston when turning the engine by hand on 96+ engines?
[This message has been edited by jmgtp (edited 11-11-2003).]
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07:47 PM
ryan.hess Member
Posts: 20784 From: Orlando, FL Registered: Dec 2002
To correct point 1... ... The earlier 91-93 or "Twin dual cam" engines were not interference, and you could do whatever you wanted with them without having to worry about valves. The 94(?)-96 "DOHC" were interference engines.
Yes, you should be. If you loosen all the cam sprockets, you will have piston contact. That's why you need to do the timing 1 bank at a time.
You cant time both banks at the same time anyways so I dont see where youre going with this. How would you seat the belt before timing the engine if the valves would hit the pistons? When the old belt comes off the cams will move, theres no stopping them. So once the old belt is off the camshafts are already out of time in relation to the crank, meaning the crank has to be turned while the cams are not in motion. What I'm trying to figure out is if when cam flats are facing up the valves would be situated in such a way that they would not strike the pistons (ie at 0 lift or something less than full lift) or if there is a certain specific order to do things that will prevent valves from striking pistons.
I really need input from someone who has timed a 96+ engine.
[This message has been edited by jmgtp (edited 11-11-2003).]
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10:14 PM
Nov 12th, 2003
gascarracer Member
Posts: 129 From: Batavia, Ohio, USA Registered: Apr 2003
Ah... I remember Mike Smith from an old yahoo board. Very cool guy, very knowledgable as well.
From what I gather from his page he discusses adjusting the cams individually but not the process of belt replacament. Since he is only doing 1 bank at a time and the engine is at TDC before he starts and adjusts the cams by only moving the crank X amount degrees from TDC, the valves striking pistons arent an issue. I'm trying to find find if should the cams remain still and the crank turn 360* if I'll have a problem (ie when seating the belt before timing it or simply after removing the belt and all cams move).
Thank you all for your responses it is much appreciated!
-john
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10:32 AM
Nov 13th, 2003
gascarracer Member
Posts: 129 From: Batavia, Ohio, USA Registered: Apr 2003
Just so you know, when you have the cam locking tool in place, there is no way that the piston will strike a valve, since they are all pretty much closed. So, having said that, you want put both lockdowns on. with the old belt still in place, set one set of cams so the flats are up, Loosen the cam sprockets (using the proper tool to hold the sprocket!, NOT THE LOCKDOWN TOOL!) and tap them lightly on the back till they are alittle loose, they will spin without the cams. Make sure the flats are up, and put on the lockdown tool. then rotate the motor 360º loosen the other sprockets and put a 2nd lockdown tool on that set. Change the belt. Set the crank at TDC, tighten one pair of cams on a the same head (doesnt matter witch), remove the lockdown tool on that head, then rotate the engine exactly 360º then tighten the other two cam sprockets. Remove the other lockdown tool. Done. This is the only safe way I know of doing this procedure.
I am assuming you know how the tensioner works, and put the belt on properly in the first place. If you need to know how this is done ask, and Ill get back to you.
Originally posted by Fierobsessed:Just so you know, when you have the cam locking tool in place, there is no way that the piston will strike a valve, since they are all pretty much closed.
thank you! that is exactly the information I was looking for. I have the tools from when I did my 91. I know that the pullies changed in 94 and then again in 96 so I hope my pulley holder designed for the 91 (I had these custom made) will fit in the notches in the 96 pulley. At least I won't need to use the pulley puller with the redesigned lock rings.
thanks again all!
o and gascarracer... if you have the procedure from the GM manual for the 96 I'd be interested in taking a look at it, I have the GM manuals for the 91, the procedure seems like it will be the same. I wonder if they fixed the error that was evident in the 91 GM manual (they instruct you to time the engine with both banks cam flats face up at the same time, without mention of turning the engine 360* to time one bank at a time).
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02:14 PM
DreXteR Member
Posts: 1763 From: Orlando, FL Registered: Aug 2000
PPL say that the 96+ engine is interfirience but I doubt it.
Here what I found:
The only diference is in the shape in the combustion chamber. The block is the same, there is no trace of diff pistons as far I know. Whats is pretty obious is the chamber it self and the only change in compression is .2 I dont say isnt interfireince or not but im skeptical about that.
DreX
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03:05 PM
coinball Member
Posts: 1526 From: Raleigh, NC, USA Registered: Apr 2002
the C/R difference in the TDC and DOHC motors was .5 not .2 still probably not enough to make a difference but i know for a fact tha 96+ DOHC pistons have a dome in them, not a flattop with valve reliefs like the 91-95 TDC's...i'm pretty sure like Fierobsessed said that almost all the valves are closed when the cam flats are locked down...
------------------ Eric '87 GT Gold/Tan 4-speed Soon to be Turbo T-top
SAVE THE SHAUN!!!
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03:11 PM
Nov 14th, 2003
gascarracer Member
Posts: 129 From: Batavia, Ohio, USA Registered: Apr 2003
Change the belt. Set the crank at TDC, tighten one pair of cams on a the same head (doesnt matter witch),
It seems to me that it should matter which bank you do first. Everything has to be in time (cams and Ignition). I beleive the Ignition sensor is on the crankshaft. Have to be sure you keep it in time.
I have the 1997 Service manual Monte Carlo. I will see if I can copy the procedure and post it later.
------------------ Ernie
1988 Silver GT One owner 47000 miles. Soon to be a 3.4 DOHC powered.
hmm. interesting point. I know the 91-93 engines dont matter, as long as you set timing to tdc the crank position sensor will know where the crank is and know how to adjust spark. Fuel is batch delivered (all 6 injectors fire at once) on the 91-93 because they are mpfi. I'd imagine the 96+ motors adjust spark using the crank sensor and since they are SFI utilize a cam position sensor on the intake cam of at least 1 bank to determine when to fire each injector. Regardless, if you have a service manual for a 97 engine I'd be very interested in the information in it as I would like to verify this. thanks again!
-john
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01:43 AM
gascarracer Member
Posts: 129 From: Batavia, Ohio, USA Registered: Apr 2003
The reason I say that It doesnt matter witch bank of cams you tighten first is because when you spin the crank around 360º its in the same place it was before you started nothing changes, as long as the cams are held in place. If the cam banks are 180 out from each other, and they each line up when the crank hits tdc, it will all be ok.
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11:36 PM
Fierobsessed Member
Posts: 4782 From: Las Vegas, NV Registered: Dec 2001