aaddpp

I have some vacation starting next week, and I am going to try and wrap up everything on the car that been unfinished since June. When I put my belt back on this past weekend I noticed the passenger side cam was off the V-mark by something like 1/8 to 1/4 of a tooth - Dwayne's writeup seems to show a similar offset. I did a search on RL, and most threads dealing with teeth offset focus on larger offsets of 1+ teeth.

Is my offset the norm? Or is this something that I should correct?

Also, as an related aside, I was wondering if someone could explain the difference with the cams at their two positions relative to the balancer? For example the cams / cam gears can be in two positions when the balancer is showing 45 degrees or TDC. Also, does it make a difference which you choose when doing work where you need to protect the valves?

Thanks,
Dave

PS -

Photo 1 - Shows engine position (TDC)
Photo 2 - Shows Drivers Side Cam Gear (proper alignment relative to V-mark)
Photo 3 - Wide shot of drivers side cam
Photos 4 & 5 - passenger cam Finding an angle that correctly shows the gear in relation to the V-mark is hard. I hope these two give a good idea.

I also have photos of the cam gears at the 45 degree mark if that helps.

Thank you for your help,
Dave

WallyP

The 45 degree positioning is just so the pistons will all be down in the bores, thus no danger of a valve hitting a piston when/if the cams rotate. Yes, the cams can be in one of two positions with the crank at 45 degrees. Either position is safe for cam rotation.

If you are changing the belt, you need to mark the cam sprockets at the existing 45 degree position prior to removal for later belt installation. You also need to carefully check cam timing at TDC after belt installation.

borland

Wally is correct about piston position.

However, WSM specifies parking the crank at 45 degrees before TDC#1 for belt removal, and then rotating cams and crank to 0 degrees TDC#1 for belt reinstallation.

So, you don't need to mark the cams if you follow the WSM for reinstallation.

blown 87

Yours needs to be set with the factory or kens tool, they do not look right to me, too close as you have noted.

It is the only way to know for sure.

aaddpp

Thank you Wally, that's what I figured with the 45 degree position. When I removed the belt, I did make marks on the cam gears at the corresponding 45 degree positions, so there was no confusion on reassembly. I did have considerably more travel (clockwise) on the passenger cam when it was without a belt. It took several tries to get it aligned at the 45 degree point as the cam would "jump" right around that point, and I would need to rotate nearly the full rotation back to the 45 degree position.

As far a checking the timing now the belt it back on, is this as simple as a visual inspection, or does it involve something like the porken timing device and/or WSM dial gauge method?

Any thoughts on the 1/4 or so tooth misalignment of the passenger cam gear shown in pics 4 & 5 (sorry the photos were not well labeled when I first posted). Is this common? Can cam timing be ok even if the v notches on the gears and back plate don't line up?

Dave

Borland, thanks. Back when I started the TB, I used Dwaynes write up. WSM method seems a bit more risky, but they must have had their reason.

Dave

fraggle

+1 for Ken's tool.

Did you spin the motor around a few times to equalize the tension all the way around?

aaddpp

Thank you Greg. I suspected that was the case. I guess I have my reading cut out for me.

Thanks,
Dave

aaddpp

I did spin the motor quite a few times to try and see if it would sort things out, but no dice.

Dave

Mrmerlin

do a search for liftbars.com
or Roger@928srus.com

aaddpp

Yup, I should have known. Checked Ken's site just after I posted, and could not edit my post quick enough

Dave

docmirror

The 'offset' you speak about is the slight difference in alignment of the tick mark on the back of the cam gear vs the notch on the backing plate. This is very common. The two tick marks will not line up exactly as its a function of the length of the belt, and the temp of the engine, also affected by the thickness of the head material and even the gasket.

There is nothing you an do about he slight offset. Make sure the teeth are lined up and get the belt on, do the tension and off you go. The only real way to set the exact cam timing is to remove the com covers and use the plunge method on the valve to set the cam location, then install the belt at TDC and secure the cam gear to the cam at that position. The tick marks are simply for the exchange belt service and do not guarantee a perfect cam to crank alignment.

Performing the cam timing is quite a bit more complicated as you must remove the cam cover, or use the Porken 32Vr timing tool which is indexed to the cam flange, and not the cam gear.

aaddpp

Thanks docmirror, I see what you are saying. Seems position of the cams relative to each other is really determine by the section of belt length which lies between them..which is in turn a function of temperature and belt age. Right now my garage is 57 degrees, and it's a new belt, so the passenger cam notch being to the right of the panel notch could very well make sense. It would seem that any slack that develops would fall to the left of the passenger cam and be absorbed by the tensioner (porkensioner in my case). That said, I think it's best for me to check the timing to be sure things are set right since I have found some other work items that were not done to correct specs. Cams are still off as well so I will have access if I try the dial indicator method in addition to the 32Vr.

Thanks,
Dave

H2

My guess is that of the many cam-belt changes happening, not all are aligned perfect, as suggested (in my mind) by the above discussion. If that's true, there must be some minimal allowable lee-way for installation, right? And if so, what symptoms might there be, if any? Some minor or hardly detectable power loss? Maybe some overheating? I'm just guessing that there are more than a few 928s on the road that don't have perfect cam alignment but the drivers can't tell the difference. Is 928 cam and belt alignment that forgiving. Comments?

blown 87

All of the ones I do are perfect as far as cam timing, or we do not do them.
But you are correct that many are out of time, the only thing I have seen it affect is idle quality.
As far as the lee-way it is spelled out in the WSM, IIRC it is + or- .1MM at the tappet.
that is not much lee-way.

aaddpp

I think it should be possible to get the indicator values for cam gear alignment and 'offset' and then see where they fall with regard to spec. I'll see what I come up with.

Dave