tomcat

Hey guys, I'm about to change my timing belt and am in need of new cam gears ('85). I read through all of the previous posts on this topic and am worried about the cam rotating when I get the old gear off.

Would indexing the exposed end of the cam to the old sprocket work? Seems if there is cam rotation, the position of the new sprocket can be indexed off of the end of the cam regardless of where the cam ends up?

(Indexing meaning marking the end of the exposed end of the cam, under the rotor, to reference a position on the cam sprocket)

blown 87

most folks really like kens set up to set the cams up, it is cheap enough that every 928 owner needs one.

I am comfortable using the old dial indicator method, but it is more work and uses more parts.

If one comes in for a t belt and does not need cam cover gaskets i will use kens set up.

tomcat

I'm not too worried about any fine adjustments. I like Porken's tool and will probably get one to make finer adjustments.

I'm more concerned about the cams rotating when the sprockets are taken off and being able to replace them correctly. I know the right cam rotated when I took the belt off last time, but I didn't have to replace the sprockets.

blown 87

The cam gears have a key slot, the only way I know to hold the cams with the gears off is under the cam covers via the flats on the cams.

you do need to get the cam close to being right as far as the same on each side or it will affect idle a bit.

tomcat

I was thinking if the cam moves when the sprocket is taken off, then the new sprocket can be put on relative to the mark on the end of the cam shaft. Then once the sprocket is tightened down, the cam can be rotated to the correct position and held by the belt.

I shouldn't have used the word "index." I meant a reference point on the exposed end of the cam, under the rotor, lining up a position on the sprocket.

JHowell37

You sure you need new gears? When I took my timing belt off the last time, the gears looked just as bad as they did when I did it the first time. But they didn't get any worse. When are you planning on doing it?

tomcat

Hey Jason,

The last time I changed my timing belt, the gears were in great condition. Currently, my passenger side is running against the outside cover and starting to rub - no rubber on the filter yet, just some fines on the gear.

I see some exposed aluminum on the right gear - I assume the left may be bad, but won't know until I take the belt off. If coating is an option, I'd rather put new gears on for time.

Really don't have much time - I'm sure I can knock this out in a day - if there are no surprises.

I think I made a mistake when I installed the belt last time. I think I read the tension for the 85-86 belt was a little higher so I adjusted the tension to the outer edge of the window on the tool.

Stromius

John..something is not right when the belt rubs and worth investigating. Post up some pics!

tomcat

It's been such a long time, I forgot how to quote posts - sorry.

Stomius,

That is an understatement and understood.

Pics right now really aren't going to show anything until I take everything apart. Previous posts mentioned bad bushings and/or a bad tensioner pivot bolt. I changed the bolt the last time per Big Dave's previous problem.

Right now, I am on schedule for a new timing belt. Looks like new cam gears are required. Maybe the other sprockets. The whole water pump discussion over the last couple of years makes me regret replacing my old water pump.

Jerry Feather

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.

tomcat

Thanks Jerry.

I changed my timing belt before - just didn't have to change the cam sprockets.

I understand what you are saying, but I know the last time I took the belt off, the cams rotated on me due to spring pressure. Doesn't matter what marks are on the sprocket if the cam moved. The cam has some play even with the keyway. I am thinking of referencing the sprocket off of the keyway also so if the cam rotates, at least I know how the sprocket should be positioned relative to the cam. Then after I tighten down the cam, I can rotate the new sprocket to the right position for the 45.

Jerry Feather

I think you are going to find that there is NO play between the cam and the sproket. If there is, there is something seriously wrong with the cam or the sproket--or, I supose, the key itself. I think your concern in misdirected and you may be overkilling this project.

tomcat

Could be. But it was my understanding the sprocket can move several degrees. If this is incorrect, then I guess all is good.

Glen McCartney

John, I think Jerry is right, you are overkilling the project. I would be concerned about how the belt is tracking if it is rubbing. That probably means the shoulder bolt on the tensioner arm is bent.
Get Kens tools for the cam timing, makes this job a snap and you know your cams are set right.

tomcat

Hey Glenn.

So if I understand this right, when I take the old sprocket off, regardless of whether the cam rotates on me, I will only be able to position the new sprocket in only one position? If this is the case, then I guess I'm ok.

I was under the assumption that the new sprocket has some play within the keyway until it is tightened down.

Then I am a little confused about the recommendations of scribing of the holes onto the backing for alignment.