DIY Engine Rebuild - Part XI (11) - Its all in the timing eh!
03-29-2006, 04:04 AM
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DIY Engine Rebuild - Part XI (11) - Its all in the timing eh!
Welcome to installment eleven...wow! In this issue I will be installing the cam chains and running through the process of timing this puppy...no its not that boring...
First of all if you remember my last screwup I had to remove the camtowers after I had glued them down to the heads because I forgot the air baffles. Here is a shot of the seperation...you can see how well the threebond adheres and forms a gasket. Nice seal...too bad I took it all apart and redid it!
There are four chain ramps in the 993. They guide the timing chains and provide a place for the chain tensioners to push in order to keep the chain relatively tight does it does not skip. Here is the long one...it has a pivot and a pushing surface. My original ones were not that bad but, since you are in there.........
Just before the ramps and chain housings are put on...
In goes a nicely prepped cam...I used MPZ breakin grease on just about everything...its wierd stuff in that it very sticky but slides nice..the cams go in nice and easy. If they bind then its possible the heads are at different hieights and the cam tower has twisted.....mine were in good shape and turned smoothly. The bearings for the cam are directly on the aluminum!
Now that the chain covers are on and the cam is in the first thing is the thrust plate. This plate holds the cam from moving back and forth, its sealed with a nice big fat Viton donut......hmmm good!
I am inserting the thrust washer next. All the parts from now on are part of the 964 backdating of the timing gear in order to use the dial guages to time the engine as well as I like the postivie lock...more on that later..
Ok, spacing. Its essential for long life of the cam chains that they be aligned with the sprockets on the layshaft in the middle of the engine. The tolerances are pretty tight so carefull measurements are taken. These shims are used to pushout the cam sprockets.
Next is the index gear. This is a funny beast, its locked to the camshaft via a woodruf key and it provides a place for the round pin to lock against to lock the sprocket to the cam... these are used ones out of an old 911 that I picked up at the junkyard!
Checking the alignment of the sprockets. You measure the offset to the cam sprockets and the main layshaft and calculate the offsets. Mine were off and I needed a 3/4 combination of spacers...exactly like the older 911's so I guess my case is very typical and correct. Luckily I picked up a set of shims at the wrecker a few months ago...(they are not a part that wears...).
In order to calculate if the sprockets are aligned you need to measure the offset to each cam sprocket, the offset to the front of the layshaft, and use the supplied offset of the front of the layshaft to the sprockets, do some math and go from there. The trick is that you are measuring thousands of an inch so the measurements have to be square and you need reasonable measuring tools...
Finally the sprocket goes on. The number of holes in the sprocket and the number of notches in the inner gear are different so no matter what position the gear is in one hole should be very close to alignment.
You can see the shims as well as the woodruf key that holds the cam assembly in place. This is why RUF, when they update a 993, throw away all the sprocket assemblies and go back to this system.
Than then putting in the tiny locking pin. Remember most 993's do not have this, its just a single machined sprocket, no keys or pins, and the sprocket is locked to the cam via the pressure of the locking nut...yeah right!
Here are both chain ramps and I am ready to put on the main sprocket. Notice the holder that I am tightening up...it provides the pivots for one of the chain ramps.
The chain tensioners should not be used to set the timing but substitued with mechanical ones...so I built one. I used an old piston brake caliper spreader and cut it up...worked like a charm!
In order to set the timing an old style rocker needs to be installed. Here are the to rockers (the one on the left is the new one, the one on the right old style). I had to grind the older one to fit since the rockers are narrower on the 993...other than that its $5 at the wrecker..
Ahh, the old fashioned setting of the valve lash. The lash is set to 0.01 mm(or 0.004") in preparation for setting the timing. This is pretty well what has been done on every 911 before the 993...and why I have the tool for it since I had a 83SC before my 993. The lash is the "slack" between the valve top and the rocker when the cam is not pressuring the valve.
Here is the cam timing tool setup for timing. You are measuring the amount the intake valve is depressed at top dead center (TDC) of the intake cycle. This amount for our cars is usually 1.0mm and can go to 1.2mm if you want to advance the cams. Its a challenge to mount the gauge since the conventional Z tool usually used for this does not fit on the 993...they changed the design of the cam towers.
The indexing pin can be pulled out with either an expensive Porsche tool or an old sparkplug...which one did I use ?
OK, timing is set and the cam is torqued down to 88 ft lbs. Notice the fancy tool to hold the cam still ; you do not want to load the chain system for this so the tool holds the cam still while the torque wrench is being reefed on...its simpler than it sounds.
OK, timing is done (after a few hours of adjusting and cursing... ) and its time to put the chain tensioners back in. Here is a shot of a chain tensioner..the cap that feeds it oil and holds the tensioner in place is on the right.
Here is the tensioner in place holding up that chain ramp...what is amazing is that the chains are kept tight by plastic ramps that were in pretty good shape on my car...
Time to put in all the rockers back in and of course change out the hydralic lifters. Lets take #2 as an example. Question : how do I tell that this is an exhaust or intake rocker??
The lifter has to be pulled from its rocker where it spent that last 10 years and several million cycles doing its job..
All the sealing oil O rings wre buggered...here is part of one that was left behind when the lifter was removed.
Comparision of the old vs. new. The biggest difference is the size and condition of the sealing O ring.
Putting a new lifter back into the rocker arm...it slips in with some pressure. Nice tight fit (after cleaning the rocker of course, blowing it out with compressed air, and lubricating the O ring).
The rocker is being installed.
All the rockers are in...
Now the chain covers to cover up those prefectly timed cams...
And its starting to look like an engine with all the essentialls covered up!!
Ok, that's about it for this installment...next time we are getting into final assembly of the engine before installation... stay tuned likelky in the next few days.....
Cheers,
Mike
First of all if you remember my last screwup I had to remove the camtowers after I had glued them down to the heads because I forgot the air baffles. Here is a shot of the seperation...you can see how well the threebond adheres and forms a gasket. Nice seal...too bad I took it all apart and redid it!
There are four chain ramps in the 993. They guide the timing chains and provide a place for the chain tensioners to push in order to keep the chain relatively tight does it does not skip. Here is the long one...it has a pivot and a pushing surface. My original ones were not that bad but, since you are in there.........
Just before the ramps and chain housings are put on...
In goes a nicely prepped cam...I used MPZ breakin grease on just about everything...its wierd stuff in that it very sticky but slides nice..the cams go in nice and easy. If they bind then its possible the heads are at different hieights and the cam tower has twisted.....mine were in good shape and turned smoothly. The bearings for the cam are directly on the aluminum!
Now that the chain covers are on and the cam is in the first thing is the thrust plate. This plate holds the cam from moving back and forth, its sealed with a nice big fat Viton donut......hmmm good!
I am inserting the thrust washer next. All the parts from now on are part of the 964 backdating of the timing gear in order to use the dial guages to time the engine as well as I like the postivie lock...more on that later..
Ok, spacing. Its essential for long life of the cam chains that they be aligned with the sprockets on the layshaft in the middle of the engine. The tolerances are pretty tight so carefull measurements are taken. These shims are used to pushout the cam sprockets.
Next is the index gear. This is a funny beast, its locked to the camshaft via a woodruf key and it provides a place for the round pin to lock against to lock the sprocket to the cam... these are used ones out of an old 911 that I picked up at the junkyard!
Checking the alignment of the sprockets. You measure the offset to the cam sprockets and the main layshaft and calculate the offsets. Mine were off and I needed a 3/4 combination of spacers...exactly like the older 911's so I guess my case is very typical and correct. Luckily I picked up a set of shims at the wrecker a few months ago...(they are not a part that wears...).
In order to calculate if the sprockets are aligned you need to measure the offset to each cam sprocket, the offset to the front of the layshaft, and use the supplied offset of the front of the layshaft to the sprockets, do some math and go from there. The trick is that you are measuring thousands of an inch so the measurements have to be square and you need reasonable measuring tools...
Finally the sprocket goes on. The number of holes in the sprocket and the number of notches in the inner gear are different so no matter what position the gear is in one hole should be very close to alignment.
You can see the shims as well as the woodruf key that holds the cam assembly in place. This is why RUF, when they update a 993, throw away all the sprocket assemblies and go back to this system.
Than then putting in the tiny locking pin. Remember most 993's do not have this, its just a single machined sprocket, no keys or pins, and the sprocket is locked to the cam via the pressure of the locking nut...yeah right!
Here are both chain ramps and I am ready to put on the main sprocket. Notice the holder that I am tightening up...it provides the pivots for one of the chain ramps.
The chain tensioners should not be used to set the timing but substitued with mechanical ones...so I built one. I used an old piston brake caliper spreader and cut it up...worked like a charm!
In order to set the timing an old style rocker needs to be installed. Here are the to rockers (the one on the left is the new one, the one on the right old style). I had to grind the older one to fit since the rockers are narrower on the 993...other than that its $5 at the wrecker..
Ahh, the old fashioned setting of the valve lash. The lash is set to 0.01 mm(or 0.004") in preparation for setting the timing. This is pretty well what has been done on every 911 before the 993...and why I have the tool for it since I had a 83SC before my 993. The lash is the "slack" between the valve top and the rocker when the cam is not pressuring the valve.
Here is the cam timing tool setup for timing. You are measuring the amount the intake valve is depressed at top dead center (TDC) of the intake cycle. This amount for our cars is usually 1.0mm and can go to 1.2mm if you want to advance the cams. Its a challenge to mount the gauge since the conventional Z tool usually used for this does not fit on the 993...they changed the design of the cam towers.
The indexing pin can be pulled out with either an expensive Porsche tool or an old sparkplug...which one did I use ?
OK, timing is set and the cam is torqued down to 88 ft lbs. Notice the fancy tool to hold the cam still ; you do not want to load the chain system for this so the tool holds the cam still while the torque wrench is being reefed on...its simpler than it sounds.
OK, timing is done (after a few hours of adjusting and cursing... ) and its time to put the chain tensioners back in. Here is a shot of a chain tensioner..the cap that feeds it oil and holds the tensioner in place is on the right.
Here is the tensioner in place holding up that chain ramp...what is amazing is that the chains are kept tight by plastic ramps that were in pretty good shape on my car...
Time to put in all the rockers back in and of course change out the hydralic lifters. Lets take #2 as an example. Question : how do I tell that this is an exhaust or intake rocker??
The lifter has to be pulled from its rocker where it spent that last 10 years and several million cycles doing its job..
All the sealing oil O rings wre buggered...here is part of one that was left behind when the lifter was removed.
Comparision of the old vs. new. The biggest difference is the size and condition of the sealing O ring.
Putting a new lifter back into the rocker arm...it slips in with some pressure. Nice tight fit (after cleaning the rocker of course, blowing it out with compressed air, and lubricating the O ring).
The rocker is being installed.
All the rockers are in...
Now the chain covers to cover up those prefectly timed cams...
And its starting to look like an engine with all the essentialls covered up!!
Ok, that's about it for this installment...next time we are getting into final assembly of the engine before installation... stay tuned likelky in the next few days.....
Cheers,
Mike
03-29-2006, 07:38 AM
#4
Race Car
So what do you charge for a rebuild 
As capable as I am when it comes to cars, I wouldn't even consider doing what you are doing. Amazing stuff for a DIY'er......you've obviously done this stuff in a previous life
As capable as I am when it comes to cars, I wouldn't even consider doing what you are doing. Amazing stuff for a DIY'er......you've obviously done this stuff in a previous life
03-29-2006, 08:07 AM
#5
Three Wheelin'
Awesome... I like your attention to detail, detail, detail... You look like you are taking your time and doing it right. There is no room for error, and by doing it yourself, you know it was done right.
Keep up the good work and posting the pictures!!!
Keep up the good work and posting the pictures!!!
03-29-2006, 09:28 AM
#6
Seared
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Mike,
Once again, a fantastic write-up. I am in awe.
I've read that a portion of the early 993s came with the 964-style keyed cam sprockets. Is that correct? I have a 7/94 build date.
Andreas
Once again, a fantastic write-up. I am in awe.
I've read that a portion of the early 993s came with the 964-style keyed cam sprockets. Is that correct? I have a 7/94 build date.
Andreas
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03-29-2006, 12:09 PM
#11
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Originally Posted by AOW162435
Mike,
Once again, a fantastic write-up. I am in awe.
I've read that a portion of the early 993s came with the 964-style keyed cam sprockets. Is that correct? I have a 7/94 build date.
Andreas
Once again, a fantastic write-up. I am in awe.
I've read that a portion of the early 993s came with the 964-style keyed cam sprockets. Is that correct? I have a 7/94 build date.
Andreas
