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I have my 92 GTS out of commission while I wait for the fan final stage controller to get rebuilt. I have the fan assembly out to replace those as well. Today I decided to inspect the timing advance/retard since I had easy access to the cams. I was surprised to discover that both cam gears seem to be offset by one or possibly two teeth in relation to TDC on the crank.
I'm not sure how long this was like this. I've been driving the car since I purchased in in Jan and the is a record of a timing belt service 2-years/5000-miles ago.
I've never done a timing belt job but I guess it's time for the next level of learning. Sigh, I was really hoping that I would be good for a couple of years.
It was suggested that I 're-string' the belt, but I am unclear how to do that so I am hoping to get some advice on from the list.
Last edited by Michael Benno; 09-20-2021 at 02:38 AM.
It's not that I distrust your degree wheel, but I don't trust your degree wheel. If you have or can borrow a dial indicator, use the old school method and check the TDC with the plug out, and the rod down on the piston. If you really want to go wild, you can take both cam covers off, and use the dial indicator on the lifter like the book says. Beware, the description in the book for setting exact cam timing is idiotic, and will require 3 or 4 read-throughs before you get it.
From what I see there you don't need a TB job, but depending on the timing error, you may need to set the timing correctly. Easier with 4 pair of hands, and four of those medium size black paper clasps.
The chaps have given you the basic info you need. The cam sprockets have 48 teeth, one tooth represents 7.5 cam degrees or 15 crank degrees. As I recall the 32VR tool is calibrated in crank degrees and can measure plus or minus 10 crank degrees. Observation of you photos logically suggests that both banks are advanced by one tooth or 15 crank degrees. This "error" will favour low end torque at the expense of top end power. Ken did an excellent thread about his efforts in this regard a coule of years ago- you might do well to read this.
When threading the belt it is quite a common rookie error to get the 1/4 cam a tooth out but both banks out one tooth I suspect is rather unusual. That someone fitted that damper suggests an enthusiastic previous owner so I am left wondering if what you see is not a mistake but rather a deliberate move to tune for low end torque which is where most owners drive most of the time. A GTS tuned like this probably pulls like a freight train.
To test for TDC take something like a wooden chopstick or BBQ skewer and use as a dipstick. Set No1 to TDC as per your damper index and put an ink mark against a reference point like the spark plug point of entry into the head. Then test for depth at say 10 degrees before abd after TDC to ensure accuracy. I doubt you will find an indexing error but vital to eliminate it.
Once you know the timing is what the 32VR tool says it is you then make a choice as to whether you like what you have or want the top end optimised. Assuming the cams are currently 15 crank degrees advanced you should be able to recover about half of that margin using the 32VR to assist the retard adjustment but you will not recover the full amount as it will be out of adjustment span range. Such would thus require belt removal or so I would think.
No need to change belt or water pump but you would have to go through the same procedure of removing accessories and the belt cover- a good dry run practice for a future TB/WP job.
It really looks like both cams are off by one tooth...
To minimize the time needed to get this fixed, I would recommend to get a dial indicator measuring tool. Take the plug for cylinder #1 out and confirm TDC of your harmonic balancer with the dial indicator. Measuring TDC on top of the piston directly.
I don't think that the balancer is wrong, as I use the same on my GTS.
After TDC on the crank is confirmed, you can start to set the cams again.
It really looks like both cams are off by one tooth...
To minimize the time needed to get this fixed, I would recommend to get a dial indicator measuring tool. Take the plug for cylinder #1 out and confirm TDC of your harmonic balancer with the dial indicator. Measuring TDC on top of the piston directly.
I don't think that the balancer is wrong, as I use the same on my GTS.
After TDC on the crank is confirmed, you can start to set the cams again.
Good luck and keep us updated.
Wow! That's a GREAT idea! Surprised no one else thought of that.
Aviation tells you one thing: "Keep it simple stupid!"
Aye-vee-aye-shun? What's that?
BTW, my plane is SO simple they left one of the flight controls completely off. It's also 70 years old in Oct. So simple, my prop is electric, and my fuel injector is a carb in disguise.
....If the damper is off by 8-10 degrees, all one needs is a screwdriver on top of #1 piston and turn the engine over by hand to detect that.
If you need to know closer than a couple of degrees, a piston stop is the best tool.
A dial indicator works, but because of the dwell time at TDC, you have to use it exactly like a piston stop.
BTW, I wouldn't question/bother checking this if the damper/hub was mine.
Thank you for all the good insight everyone. I'll start with verifying the TDC mark on the damper matches to what cycler 1 is doing. I don't have a dial indicator handy but I like Fred's chopstick idea, seems easy enough to start there
....If the damper is off by 8-10 degrees, all one needs is a screwdriver on top of #1 piston and turn the engine over by hand to detect that.
If you need to know closer than a couple of degrees, a piston stop is the best tool.
A dial indicator works, but because of the dwell time at TDC, you have to use it exactly like a piston stop.
BTW, I wouldn't question/bother checking this if the damper/hub was mine.
I missed your response, it came in as I was typing the above. Yeah, I agree given the damper design and woodruff key, I cant see how it could be off at all. It will be good to verify for my own entertainment/learning.
Last edited by Michael Benno; 09-20-2021 at 07:59 PM.
I missed your response, it came in as I was typing the above. Yeah, I agree given the damper design and woodruff key, I cant see how it could be off at all. It will be good to verify for my own entertainment/learning.
You would be amazed at what I see on a daily basis...
Therefore, I assume almost nothing.
It's doubtful the damper is wrong, so let's assume for now it is correct.
That means that the cams are incorrectly indexed with respect to the crankshaft by 1-tooth.
The fix is:
Remove the front of the engine to expose the timing belt
Mark or draw a line on the timing belt where it should be on the cam-gears (..in this case, 1-tooth to the left)
Completely loosen the tensioner
Remove the timing belt from both cam-gears only
Start at the right cam gear, get a wrench and rotate cam-gear until its mark/index aligns with your new mark/line on the belt
Go to the left cam-gear and do the same
Tension the belt
Verify your cam-gear indexes line up with backing-plate's mark
Install the front of the engine.
09-20-2021, 01:57 AM
Timing belt offset a tooth or two!?
