Timing Belt Question

[perfimage]

Hi guys, I just want to say that this one awesome forum. Lots of info and opinion concerning our beloved 60* V6 power plants.

Now for my question.

When spring finally breaks, I will be changing the timing belt in my 93 Z34. At the moment,m it is running just great with a couple of minor exceptions, (occasional SES light referencing an ERG code and an ANTI-LOCK light that comes on between 68-72 mph). I bought the car with 87k miles on it , it is now at 107. I have NO idea when the timing belt was last changed, if ever, though I see someone had the inspection cover, as evidenced by the oddball fastener holding one end of it down.

I have read and thoroughly understand ALL the information regarding changing the belt, but I do have to wonder a thing or 2.

My idea was to prepare the enginf for the belt change, set #1 to TDC, etc. But I am unsure if it is REALLY necessary to go through the entire cam timing procedure, my reasons:

1. If the engine is running and the cam sprockets are that difficult to remove, they shoudl not have moved at all, so there SHOULD be no reason to retime the sprockets to the cam.

2. With the engine set to #1 TDC, you should be able to slip the old belt off and slide the new one right back on and be in good shape. I know there is most likely some bels stretch that must be accomodated for, this is where my next procedure applies.

3. Before removing the old belt, mark places on both the sprockets and the belt. Then simply transfer those marks to the new belt, and align them all.

For instance, starting at the drive sprocket, count the number of teeth between the mark on the drive sprocket and each subsequent mark on all sprockets. Then, mark the new belt at the corresponding teeth on the new belt and install, aligning the marks on the belt with the marks on the sprockets.

Now hang on just a minute before going ballistic. The key here is NOT to transfer the marks from the old belt to the new one by measurement, but by belt tooth count. Since the sprockets and belts have a certain and identical tooth pitch, the cam timing will be set correctly which will eliminate any out of time condition due to belt stretch.

Any thoughts on this?

Thanks!

RED

[Lyle's GTP]

Nice idea, But because of the tensioner in there, you'll never get all the cogs to go in the right spots. But as soon as you release the tensioner it pulls the cams out of whack. I have not read the procedure on this site yet, but to saveyour self a hugh pain in the ass, I would use the hold down tool. You are right about not releasing the cam sprockets, you shouldn't have to.

Lyle

[perfimage]

You are right about the tensioner, but because it does it's job after everything else is already timed, it should not make a difference so long as the old belt and sprockets are marked before anything is released, and the new belt and sprocket marks stay aligned until the tensioner is back in business.

This whole process obviously implies that you start at the drive sprocket and work your way through aligning everything one piece at a time tll you reach the tensioner.

RED

[SappySE107]

Its much harder to do what you are talking about than it is to think of it. I can't imagine trying to get the belt on with the tensioner in place. Even so, you would have to have the cams flat up and mark the gears, and the other set cam flats down and marked...unless you do them both up and then arrange the 1 set with the marks apart from each other instead of next to each other.

[Lyle's GTP]

The thing is........ I tried this once. weeving the belt trough trying to keep it all tight, But as soon as you let the tensioner go it pulls the belt and knocks out the timing. It doesn't take much to screw up the idle.

Lyle

[perfimage]

ok...heres the deal.

First I am not trying to convince anyone that it will work or that it is right, so please do not perceive my persistence as such. I am trying to make sure it is understood and from what I am reading, you are not, and part of that could be my explanation.

The tensioner does not make a bit of difference, so long as the marks are all lined up before and then when the tensioner is put back in the loop.

Please follow this and picture what is happening.

With the engine set at TDC (not necessasry, but if things go awry, it will help put them back), pick a tooth on each sprocket and mark it. The tooth MUST be on a part of the sprocket where the belt is in contact, now put a cooresponding mark on the belt for each mark you placed on the sprocket. Do this for EACH toothed sprocket BEFORE releasing the tensioner.

Now release the tensioner and remove the belt and count the number of teeth between each mark, starting with the one that cooresponds to the drive sprocket mark at 0. the numbers that follow are for demonstration purposes, not actual tooth count. Lets say you count 100 teeth from the drive sprocket mark to the mark on the first cam sprocket then 15 teeth to the #2 cam sprocket mark. Around the idler and to cam #3 we go with 130 teeth to the mark and another 15 teeth to the mark on the #4 cam sprocket.

Now with the new belt in hand, pick a tooth and start counting, when you reach 100, place a mark on the belt. Now count out each of the other marks and mark the teeth accordingly.

With one specific tooth marked "0", you will have marks at 0, 100, 115, 245, and 260.

Now slide the belt on, starting at the drive sprocket and your "0" mark, up over the first idler and to #1 cam sprocket, align belt tooth 100 with your mark on the sprocket, your next mark with the mark on #2 sprocket and so on till all 5 marks are aligned with the marks on their respective cam sprockets.

Now at this point, the cams should be timed, remember, the timing is relative to one another and the belt based on the tooth count, NOT anything else. So long as the belt doesnt jump a tooth it will remain timed.

You will see a little movement of the cams when putting the belt on, which would be normal, as the new belt is sure to be a little shorter than the old one. This movement will bring the cams back in to correct timing. You will also most likely see a bit of movement when the tensioner is put back in place, this would also be normal as the belt tightens and the slack between each sprocket is taken up. Again, so long as all the marks remain lined up, you will still be timed correctly. Remember the timing is being set by the number of teeth between the marks. This is possible because the pitch of the teeth on the new belt and sprockets are identical and the teeth keep it all in time.

Teh tensioner has no affect as this takes up the slack left between the last cam sprocket and the drive sprocket, which does not have ANY affect on the timing unless the belt stretches top a point that the tensioner cannot take up th slack.

Thanks for the input!!

RED

[Lyle's GTP]

Well you sound pretty sure you can do it. Give it a try let us know how it turns out.

Lyle

[jmgtp]

Theres only one way to do the belt. Use the proper procedure (listed somewhere in the site) and the right tools or custom made equivalent. If youre not going to do it right why bother at all?

[perfimage]

For the same reason there are many other tips and tricks posted in these forums, to save some time and effort while accomplishing the same result.

The full blown procedure as posted on the site is definitely the way to do it after a belt failure, or during an engine build up, however this is replacing a part on a good already running engine.

Several areas are identified that can affect the cam timing and ultimately performance.

The biggest one, the crank to cam timing. If this is off, its a failure no matter what, this can be affected by a few things:

1. Sloppy/loose internal timing chain. Rarely an issue based on the number of times it is referenced in these forums.

2. Stretched belt. Usually the reason for replacing the belt in the first place and probably the biggest factor in overall performance of this engine once running.

3. Cam sprocket to camshaft timing. Often discussed here but in my opinion, not much of an issue unless the engine has suffered a belt failure or if being built for the first time. I see no reason this should need to be addressed once set at build up, if it does slip, there is more wrong than meets the eye, and then you need to look deeper for the problem and reset things once the problem is identified and corrected.

Given the 3 areas, the only one that is of real concern in the normal scheme of things is the belt, and since the belt is keeping only the cam and drive sprockets in line with one another, I see no reason to dig into an already running engine to to retime something that is probably not out of time anyway.

Do not misunderstand me at this point, I am no rookie when it comes to engines, I have built my share of pushrod engines and fully understand the delicate relationshop between cam and crank. Therefore this is not some hair brained idea conjured up by someone that hasn't got a clue in the first place, it was well thought out idea that is being presented to a group of peers to discuss and to ponder.

I am hoping to rouse meaningful discussion of a possible new way to do an old job, not attract criticism about doing the job right.

Thanks again for the input folks!

I will let you all know how this goes when I tackle it in a few months. If able to, I will take pics and post them as well.

Cheers!

RED

[jmgtp]

Doing it any way other than the by the book is sloppy. There is no other way to get it perfect. It will be off. If you put the engine at tdc#1 and remove the belt then only 1 bank will have its cam flats up. The other bank will be face down, so you could only put the hold down on 1 bank, the other bank will move, guranteed. If youre satisfied with less than perfection in something as critical as a timing belt then by all means cheeze it any way you want. Personally I'd spend the extra time to do it the right way.

[brian89gp]

When I took my belt off (did not replace, just removed it) I marked the belt and cogs in 2 places per cog with a paint pencil, in the grooves on the 4 cam cogs and the teeth on the 1 drive cog. When I put it back on I just aligned the marks so everything lined up.

The only problem I see with yours is transferring the marks over to a new belt, there are plenty of teeth and its probably pretty easy to miscount. I can see it working though, I would just double check to be sure the cams are flat with the new belt, just to be sure.

[perfimage]

Ok here we go. I have all the parts either in hand or ordered and ready to try this as I described. I intend to document this with pics and will verify the cam flats are lined up as expected once the new belt is in place. I will let you all know how this goes.

One question I do have is this. I have the tensioner pulley but I am not sure it is the right one, even though all the parts stores in my area insist it is.

Part Info:
DAYCO IDLER/TENSIONER PULLEY
P/N 89010
82MM FLAT WITHOUT FLANGE

[grandprixgtp_91]

ok, here is a good reason to unbolt the cams, first, i tried it the way you want to my first time, and the car never ran properly, i kept trying it and i could never get it. second, the timing chain stretches so unbolting the cams will make up for the chain stretch. just do it properly you will save a headache.

Jake

[grandprix34]

As far as I know the tensioner pulley comes with the tensioner arm/bracket with a little cup at the end of the bracket to hold the tensioner actuator...

from what I learned around my town, THE PARTS STORES DO NOT CARRY the tensioner ACTUATOR or the tensioner pulley. These are dealer only items unless your parts store is friendly enough to buy 'em for you (had an O'Reilly's guy do that for me cuz he's cool like that). Replace everything and that includes the $90 actuator,

This thing:


The tensioner pulley has the hole for the bolt offset. To get a better idea of what I'm talking about go to the 60 degree homepage and SAVE BACKGROUND and you will see the pic oc the DOHC timing layout...

Here the part #'s:
tensioner pulley - 24503561 bolt - 10162013
tensioner actuator - 24503860

[bud36light]

Im not saying you cant do this job like you are saying and at least in theory it sounds like it can work. However once you have done this particular procedure at least in my opinion unbolting the sprockets is the the way to go. that belt is pretty stiff and even with the sprockets unbolted it is a decent challenge to just get the belt routed around the loop. And remember it has to stay perfectly clean or it will(not could) lead to pre mature failure. I mean this is not that bad of a job anyway once you get the FUCKING sprocket bolts loose. Any way if you do this another way I think we all would be interested. Let us know.(roughly how long and bitch factor)