Cam Gear Change
04-10-2010, 05:36 PM
#16
Rennlist Member
John, I am not familiar with the idea of scribing the holes on the back plate, but I suspect that is simply a substitute for transferring the 45 degree mark from the old sproket to the new as I suggested above. I would be concerned that using the scribe-the-holes method may be subject to some error since I suspect that the holes are cast-in rather then machined-in and I would be concerned that they may not be in the same proximity to the keyway and the teeth on each sproket. If they are, again, I think you are doing the same thing by simply marking one tooth on the new sproket to match with the timing mark on the back plate.
04-10-2010, 05:43 PM
#17
Drifting
John,
It's not unusual after removing the belt for the cam to slip and rotate back a few degrees as you experienced.
As you know, the cam sprocket holder is keyed to the cam, while the sprocket is bolted through an eccentric hole. What you can do is use this photo and a caliper to measure before you remove the center bolt and old cam sprocket per the WSM instructions. This is a very accurate way to restore the cam gear when compared to marking the inside of the eccentric hole
It's not unusual after removing the belt for the cam to slip and rotate back a few degrees as you experienced.
As you know, the cam sprocket holder is keyed to the cam, while the sprocket is bolted through an eccentric hole. What you can do is use this photo and a caliper to measure before you remove the center bolt and old cam sprocket per the WSM instructions. This is a very accurate way to restore the cam gear when compared to marking the inside of the eccentric hole
04-10-2010, 05:44 PM
#18
Rennlist Member
You can change out the cam sprockets without affecting timing, just turn the crank until the camshaft you are working on is not loaded, but it is a lot better to take the opportunity to adjust them properly as a WYAIT.
04-10-2010, 05:56 PM
#19
Burning Brakes
Thread Starter
Borland,
I stared at the pic you posted for sometime this week. It's starting to make some sense to me now. I think the reference outlined in the pic is similar to what I was implying, but I think your method is easier.
Martin,
I may be getting a little confused about a lot of things - it's been a while. I just remember when installing my belt last time, the left cam did rotate. And there were a few posts where guys were changing their sprockets and the cam rotated and they lost their reference. I do not want to have to time the engine through the spark plug holes and I do not want to remove the cam covers again.
I don't know if you made SITM last year - sorry I didn't. Hopefully we'll make it together this time.
I stared at the pic you posted for sometime this week. It's starting to make some sense to me now. I think the reference outlined in the pic is similar to what I was implying, but I think your method is easier.
Martin,
I may be getting a little confused about a lot of things - it's been a while. I just remember when installing my belt last time, the left cam did rotate. And there were a few posts where guys were changing their sprockets and the cam rotated and they lost their reference. I do not want to have to time the engine through the spark plug holes and I do not want to remove the cam covers again.
I don't know if you made SITM last year - sorry I didn't. Hopefully we'll make it together this time.
04-10-2010, 06:23 PM
#20
Under the Lift
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Regardless of the cam moving off a lobe while the gear is off, it will probably move more when you tighten the new gear on. So, you are right to be concerned about having a reference point. When I first did it, I just made marks on the gear face at the centerline of each of the 3 bolts and transfered them to the new gear. It was "eyeball" accurate versus Borland's better caliper measurement. I now use Ken's tool, but you can get it the same as before with Borland's idea. Even my original eyeball marking was right on in that regard. But what you don't know is whether it was at spec to begin with.
04-10-2010, 06:36 PM
#21
Burning Brakes
Thread Starter
Thanks Bill.
I feel reassured. Porken's stuff is so sophisticated I need to read over his stuff several times, each time, to figure out what he is doing. But I get it in terms of restoring to previous, but might not have been correct to start with.
I feel reassured. Porken's stuff is so sophisticated I need to read over his stuff several times, each time, to figure out what he is doing. But I get it in terms of restoring to previous, but might not have been correct to start with.
04-10-2010, 07:40 PM
#22
Rest in Peace
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Someone else has sort of off-handedly mentioned that the cam sproket has a key way. Actually the cam sprokets are mounted to the end of the cam shafts with a key and keyways. That means that the sproket can mount on the end of the cam shaft only in one position. What I suggest you do is set the crank at the 45 degree position in accordance with the instructions (you are following John Pirtle's timing-belt Procedure, aren't you? If not, go to 928 international's web site and find it and print it out and use it like it is your bible). Then mark the cam sprokets at the timing mark with an appropriate marking substance. Then take the sproket off and match it up with your new sproket so the key ways are in line with each other then transfer the mark to the new sproket. Now, put the new sproket on the end of the cam shaft with the key in the matching keyways and tighten it up. If the new mark does not line up with the timing mark on the belt housing that means that what you are in fear of has happened--the cams moved!!! If they did, rotate the cam sproket and cam(s) back so they line up. Problem solved.
There is a key way for the y shaped adapter, the movement you get is on the long slotted holes in the gear.
They tend to crack at the keyway, so look at them with care for any signs of problems.
04-10-2010, 11:00 PM
#24
Rennlist Member
John,
Mine moved when we were doing the belt and gears. Eventually used Ken's tool to set it back to stock.
I would go with Borland's suggestion for now. Ken's set up took a little time to get my head around, but wow, once the light comes on, worth every penny.
Best,
Rob.
Mine moved when we were doing the belt and gears. Eventually used Ken's tool to set it back to stock.
I would go with Borland's suggestion for now. Ken's set up took a little time to get my head around, but wow, once the light comes on, worth every penny.
Best,
Rob.
04-10-2010, 11:16 PM
#25
Burning Brakes
Thread Starter
Originally Posted by 928 at last
Mine moved when we were doing the belt and gears. Eventually used Ken's tool to set it back to stock.
I would go with Borland's suggestion for now. Ken's set up took a little time to get my head around, but wow, once the light comes on, worth every penny.
I would go with Borland's suggestion for now. Ken's set up took a little time to get my head around, but wow, once the light comes on, worth every penny.
Thanks. And thanks for everyone else who responded and offered your advice.
