RET

I would greatly appreciate advice: the stamped timing marks on the dampener on my '89 928 GT's engine (Devek built stroker with Scat crankshaft) have no bearing on reality.

The dampener was installed correctly (Bill Ball confirmed this), and there are some crude and nearly invisible markings in paint on it that somewhat approximated TDC, so this problem was known about before.

I am in the process of the timing belt/water pump exercise and have (...I believe...) accurately marked TDC using a dial indicator on the #1 piston, so I think that the cam timing can be set properly, but I really think that this should be fixed if at all possible before putting things back together and creating confusion and possible disaster for someone else later.

One of those little attentions to detail that are so important......

Bob

terry gt

I think that the first batch of scat cranks from Devek , the key way was 180 deg out . so be careful .

Mrmerlin

well to figure things out while facing the engine if the crank keyway is pointing close to 4 to 5 O clock then the crank is at TDC if the key points to 3 O clock then the crank is at 45 BTDC.

Going on this set the crank, put a straw into the #1 plug hole and watch to see where exactly TDC is.
fit the damper then put a mark on the damper that coincides with the pointer on the water pump, you could also mark 45 BTDC

dr bob

Sounds like you have identified #1 TDC with the dial indicator, so you have at least a starting point for "calibrating" the damper. Unfortunately, short of having a new keyway broached in the damper hub, you are low on serious options.

Were it mine...

I would make a poor-man's degree wheel on the balancer itself. Measure the diameter of the balancer ring and do a little calculator math to find the distance between 5º points on the ring. Think pi times diameter, divided by 72, and you have that 5º mark spacing. Then, I'd make a tape label to put on the ring for doing timing, with marks spaced per the calculation. You can do this in Excel or Word by building a table with precise cell spacing and printing the result at actual size (no scaling. On the balancer itself, I'd use a small triangle file to make a permanent mark at the real TDC spot at the pointer, which you determined already with the dial indicator on the #1 piston. Then whenever I need to have real marks for a belt or cam timing project, just tape the label on the balancer rim with the 0º mark on the label lined up with the 0º line you made on the balancer.

Before you get too far into this though, are you SURE you were on the #1 piston and not #5?

RET

Thanks for the replies.

Cylinder identification: hopefully #1 is closest on the left while facing the engine from the front.

Crankshaft keyway: mine is somewhere around 9 O'clock with the engine at 45BTC (sorry not to be precise, but these estimates are from memory.... also, the distributor rotors had been pointing around 3 O'clock when the crank was locked and disassembly began).

Finding TDC: place long shaft dial indicator in spark plug hole on #1 cylinder; rotate engine to bring piston to highest point on compression stroke; zero dial indicator; rotate engine clockwise until dial indicator shows that the piston has moved down 150 thousands; rotate engine counter clockwise until the dial indicator shows 50 thousands; mark dampener; rotate engine CCW past top point (0 on dial indicator) until the piston moves down and the dial indicator shows 150 thousands; rotate engine CW until the dial indicator shows 50 thousands; mark dampener; and place third mark for TDC in the exact middle of the two previously made marks.

I had originally thought that the dampener had failed until I found the painted marks.

Broaching a new keyway is not something I am equipped to do, certainly not accurately anyway. OTOH, I could turn it in the lathe to remove the old numbers and then stamp new marks and legends. I don't imagine that the minimal loss of weight would make any difference.

Perhaps some service like the Damper Doctor could rebuild mine but having it look like a stock part might not be such a good idea anyway if someone in the future decided to replace it without knowing the difference.

Bob

dr bob

If you decide to have it rebuilt, go ahead and make all the marks on it to show where TDC is now. "Rebuilding" a damper includes replacing the old bonded rubber layer with new. It would be easy to have the ring bonded back to the hub in the new position.

Broaching a keyway is an easy operation for any competent machine shop. Gears and sprockets used in industrial machinery are usually shipped without keyways when there's a need for precision timing.

mark kibort

scary that there would be parts out there like this that are not perfect from the alignment perspective.

just marking the damper is probalby the best way after you find TDC. just measure the distances for the marks on the actual stamped markings and then replicate them at the "new TDC" position. use a vibrating marker to perminately mark the new position degree values.

Mrmerlin

I would not get too crazy about doing any machining to this damper.

Keeping it simple,
add new marks with some paint,

NOTE make sure to mark the inner and outer portions of the damper,
as if this has failed you will soon see a mismatch.

RET

Thanks again for the responses.

Stan, the crankshaft keyway points towards the passenger fender while the distributor rotors point to the driver's fender while #1 is on the top of the compression stroke.

The clocking is 180 off stock as near as I can tell. The dampener was crudely marked for TDC with a splotch of paint and scrawled lettering. This corresponded to my TDC marking fairly well... at least some portion of the smeared paint was over the TDC position....

This corresponds to terry gt's response regarding the error with the early Scat crankshafts received by Devek.

I will likely fill in the stock marks with putty to hide them, make my own, and repaint the dampener in some non-stock color.

Bob

Mrmerlin

It would be a good idea to put a sticker on the engine that details the crank key way position so any mechanic thats working on this engine doesnt try to reset the crank to factory specs

GregBBRD

There's only two choices when something like this happens when manufacturing a part.

Fix it or throw it away.

It should have never made it into a customer engine.