'96 850R Very low mpg, very low power.

Post by **rspi** » 17 Dec 2012, 18:11

When the cams are ligned up with the cover the back of the cams will look like those other photos.

bmessina · Post by **bmessina** » 17 Dec 2012, 18:29

Sorry, not following. Are you saying that if all the marks are lined up correctly (cams & crank), the motor is at TDC exactly and a secondary mark would need to be made on the intake cam at TDC according to the timing scale on the cover if you wanted to use the scale & a timing light to check timing?

Post by **rspi** » 17 Dec 2012, 18:35

No, I'm saying that the only marks that I'm concerned with are the marks shown on this cover and cams in the photo I posted. When the cams are properly aligned with the cover, the rear of the cams should be in the straight line that the other photos displayed.

I was told that the motor is NOT TDC when these cams are aligned, however, the timing is properly set, as long as someone did not take the 3 sprocket bolts loose and move the cams (not sprockets) at some point.

bmessina · Post by **bmessina** » 17 Dec 2012, 18:39

Got it. Still seems like a weird way to run a motor, but I get what you're sayin'. Thanks.

Regarding the sprocket bolt "adjustment" - What is the max range of that adjustment? I might need to check that too. The bolts should be centered, right?

Post by **rspi** » 17 Dec 2012, 18:56

Not really. When the cams are aligned in the back, that is considered right/perfect. So, when the motor was built, the back of the motor was aligned like the previous photos, then the cam sprockets were bolted on, likely not totally tight, then the belt was installed, then the motor was turned a few times to make sure everything was set right. The cam sprocket bolts were torqued down, and last but not least, the marks were scribed into the cam sprockets to align with the cover notches. So the back of the cams were locked and the marks were set.

What some people do is pull those bolts not knowing that the bolt holes in the cam sprockets are slotted and can move, it happened to me. Usually when someone decides to replace the leaking front cam seals. The problem is, most don't have a bagillion marks on it like I had and end up messing up the timing a little, which could make the car run poorly. Which may have been the case with your car.

I believe the cams may be able to be adjusted about 7% either way before they come in danger of making valve to piston contact. Here is a link where some were talking about cam timing adjustments.

https://www.matthewsvolvosite.com/forums ... =1&t=53377

What I would do if I were you is align the cams to the cover and pull the stuff off the back to see if the cams are actually aligned properly with the cam sprockets.

Post by **precopster** » 19 Dec 2012, 14:07

On the 5 cylinder Timing marks on crank sprocket equates to cylinder 1 being around 2mm shy of top of travel. You can check this with a piece of wire through the spark plug hole while turning the crank to the mark. Using a timing light is therefore useless.

On the 6 cylinder whiteblock cylinder 1 is about 2inches before top of travel when crank is on mark. This is not a Ford, GM, Nissan or Mitsubishi motor in the way timing is referenced.

Post by **northernlights** » 19 Dec 2012, 17:56

FWIW, 2 mm below TDC on this engine is about 15 crank degrees. This is based on a 90 mm stroke and a 139.5 mm rod center to center length. For those who need to see the math:

Piston position = (S/2 + R) – (S/2 * cos(A) + SQRT(R^2 – (S/2* sin(A))^2))

Where S= stroke, R=rod length, A= crank angle. If you set this up in Excel watch the nested ()'s.

If you have consistent units (i.e. all mm) the answer will be in the same units.

So, with that in mind, the little tick mark should be off by about 15 crank degrees advanced or 15 degrees retarded from the notch in the cover. I am uncertain which direction it would be because it depends if it is 2 mm before or after TDC. I do not know how this equates to the 0 to 30 marks on the timing cover, but they are not there by accident, and I have to believe there is a way of checking timing.

Post by **precopster** » 20 Dec 2012, 04:42

Well it could be 3mm (never took a ruler to it) and it IS before TDC on the upstroke. I had a couple of whiteblock 5s on the engine stand and noticed the before top position when on crank mark.

Love the formulas....engineering and its relevance to the internal combustion engine is certainly an interesting thing.

Rocky · Post by **Rocky** » 20 Dec 2012, 06:03

Op photo of the sprocket put the mark far away from the notch it seemingly needs to be aligned with. How about the other sprocket?

bmessina · Post by **bmessina** » 20 Dec 2012, 15:54

Rocky wrote:Op photo of the sprocket put the mark far away from the notch it seemingly needs to be aligned with. How about the other sprocket?

Photo was taken while the engine was running, with a timing light on it, to display what the timing looks like when you hook up a light like any other car.

northernlights wrote:I do not know how this equates to the 0 to 30 marks on the timing cover, but they are not there by accident, and I have to believe there is a way of checking timing.

This is what I've been thinking, the marks wouldn't be there if you couldn't use them. The problem is the lack of another mark on the sprocket to use as a reference on the scale. Or, I guess, there may be a weird alternative way to hook up the light.

'96 850R Very low mpg, very low power.

Re: '96 850R Very low mpg, very low power.