Ccmano
05-27-2018, 12:42 PM
So I just completed the cam timing on my new (to me) engine, the ex-Johnny5 91 35k mile engine. This is the first time I have attempted this process. Very special thanks to Phil (Jagdtpanzer) who lent me some of the tools needed. In particular the chain tensioner reset tool he designed and built. Made my first time at this much more efficient and enjoyable.
Much has been written on the subject by much more experienced than me, so I just want to add a few observations.
When first looking into this process I thought it looked to be somewhat daunting. Given the engine I am working with has only 35k miles I was unconvinced that it needed the adjustment. After reading volumes on the subject including Mark Haibecks excellent article and instructions on the subject, after encouragement from fellow members and of course the fact that the engine was already out, I decided to go ahead with it.
While this process is not for the technically inexperienced I found that given the right tools and instructions it is really rather straight forward. Setting up the dial indicator and torquing the new sprocket bolts actually turned out to be the most challenging parts. It took a little while to come up with the right length and offset dial indicator probe. I ended up doing a 4-48 thread on a 2.5 in 1/8 steel rod with about a .5in offset and polished probe end where it rests on the lifter. Make sure you thread a long enough section of rod so that the offset can be positioned either to the left or to the right of the indicator. Going from intake to exhaust adjustments will require the offset to be flipped.
A solid base for the dial indicator is essential. I used a magnetic base on a fabricated steel angle iron support bracket. The same bracket I fabricated and used to lift the engine.
As Mark Haibeck writes when torquing the new sprocket bolts it is advisable to insert a piece of cardboard approx. 0.20 thick under one or two of the temporary cam retainers. This helps to fix the cam in place when doing final torquing. I found that at least a 0.20in piece is needed. I used a 0.30in thick piece on two retainers and had someone (thanks Chuck) hold the opposite end of the cam. I started with a 0.10in piece that did not work well. I found that two 0.30 pieces ultimately required very little effort from my assistant.
While I had read that these engines could be significantly off their cam timing spec direct from the factory I must say I was still surprised at what I found on this low mile engine. The 90-92 engines were supposed to have cam timing set to 114 degrees BTDC for both Intake and Exhaust.
I found the following.
Driver Intake 117 degrees
Driver Exhaust 112.5
Pass Intake 114
Pass Exhaust 115.5
I reset my cams to the Haibeck recommended 114 Intake and 110 Exhaust.
The final tricky piece is resetting the chain tensioners. It’s one of those things where until you see it for yourself it’s not totally clear how it comes together. The problem for me was even with the tensioner fully compressed in the vice, setting the top ring to retain the plunger was difficult due to the lack of space to get in there and set the ring. Doing it without Phil’s tool as Haibeck shows is the most difficult because of the proximity of the vice jaw to the working area. Just the right amount of tensioner compression and even pressure from preferably opposite sides on the ring with two small screwdriver blades is required to pop it in. Using Phil’s tool in the vice was better but I found that the force of compressing both the tool and the tensioner in the vice tended to jam the ring not allowing it to seat properly. My solution, as shown below, was to use an old plenum bolt through the center of the tool to compress the tensioner. This adds working space and in the case of Phil’s tool allows the tensioner to be compressed without any pressure on the tool. Once compressed the tool is used to simply pop the ring in place. Two final comments here. I found that the sweet spot in compression for popping the ring in is not at full compression. It’s somewhere marginally short of that. Maybe a tenth or two short of full compression. If I had to do it again I would use a wider bolt as a spacer. One that fills the gap in the head of the tensioner being compressed. It will provide more stability under compression as opposed to the plenum bolt I used. You don’t want the compressed tensioner popping out of the vice because of improper alignment in the vice. Be very careful.
Oh and one final thing that I have never seen in the write-ups. It’s probably a good idea to coat all the cam bearings and lobes in assembly lube before you start. You don’t want them running dry while your turning the engine over and over to do the timing.
Anyway, that’s it. Your results may vary. Now on to the ported top end (thanks Locobob) refinishing and getting engine in and running in time for the Rocky Mountain Run.
H
:cheers:
http://a68.tinypic.com/28gxkxh.jpg
http://a64.tinypic.com/2iihdon.jpg
http://a63.tinypic.com/1zxuv08.jpg
Much has been written on the subject by much more experienced than me, so I just want to add a few observations.
When first looking into this process I thought it looked to be somewhat daunting. Given the engine I am working with has only 35k miles I was unconvinced that it needed the adjustment. After reading volumes on the subject including Mark Haibecks excellent article and instructions on the subject, after encouragement from fellow members and of course the fact that the engine was already out, I decided to go ahead with it.
While this process is not for the technically inexperienced I found that given the right tools and instructions it is really rather straight forward. Setting up the dial indicator and torquing the new sprocket bolts actually turned out to be the most challenging parts. It took a little while to come up with the right length and offset dial indicator probe. I ended up doing a 4-48 thread on a 2.5 in 1/8 steel rod with about a .5in offset and polished probe end where it rests on the lifter. Make sure you thread a long enough section of rod so that the offset can be positioned either to the left or to the right of the indicator. Going from intake to exhaust adjustments will require the offset to be flipped.
A solid base for the dial indicator is essential. I used a magnetic base on a fabricated steel angle iron support bracket. The same bracket I fabricated and used to lift the engine.
As Mark Haibeck writes when torquing the new sprocket bolts it is advisable to insert a piece of cardboard approx. 0.20 thick under one or two of the temporary cam retainers. This helps to fix the cam in place when doing final torquing. I found that at least a 0.20in piece is needed. I used a 0.30in thick piece on two retainers and had someone (thanks Chuck) hold the opposite end of the cam. I started with a 0.10in piece that did not work well. I found that two 0.30 pieces ultimately required very little effort from my assistant.
While I had read that these engines could be significantly off their cam timing spec direct from the factory I must say I was still surprised at what I found on this low mile engine. The 90-92 engines were supposed to have cam timing set to 114 degrees BTDC for both Intake and Exhaust.
I found the following.
Driver Intake 117 degrees
Driver Exhaust 112.5
Pass Intake 114
Pass Exhaust 115.5
I reset my cams to the Haibeck recommended 114 Intake and 110 Exhaust.
The final tricky piece is resetting the chain tensioners. It’s one of those things where until you see it for yourself it’s not totally clear how it comes together. The problem for me was even with the tensioner fully compressed in the vice, setting the top ring to retain the plunger was difficult due to the lack of space to get in there and set the ring. Doing it without Phil’s tool as Haibeck shows is the most difficult because of the proximity of the vice jaw to the working area. Just the right amount of tensioner compression and even pressure from preferably opposite sides on the ring with two small screwdriver blades is required to pop it in. Using Phil’s tool in the vice was better but I found that the force of compressing both the tool and the tensioner in the vice tended to jam the ring not allowing it to seat properly. My solution, as shown below, was to use an old plenum bolt through the center of the tool to compress the tensioner. This adds working space and in the case of Phil’s tool allows the tensioner to be compressed without any pressure on the tool. Once compressed the tool is used to simply pop the ring in place. Two final comments here. I found that the sweet spot in compression for popping the ring in is not at full compression. It’s somewhere marginally short of that. Maybe a tenth or two short of full compression. If I had to do it again I would use a wider bolt as a spacer. One that fills the gap in the head of the tensioner being compressed. It will provide more stability under compression as opposed to the plenum bolt I used. You don’t want the compressed tensioner popping out of the vice because of improper alignment in the vice. Be very careful.
Oh and one final thing that I have never seen in the write-ups. It’s probably a good idea to coat all the cam bearings and lobes in assembly lube before you start. You don’t want them running dry while your turning the engine over and over to do the timing.
Anyway, that’s it. Your results may vary. Now on to the ported top end (thanks Locobob) refinishing and getting engine in and running in time for the Rocky Mountain Run.
H
:cheers:
http://a68.tinypic.com/28gxkxh.jpg
http://a64.tinypic.com/2iihdon.jpg
http://a63.tinypic.com/1zxuv08.jpg