Intake Cam Timing Offset?

[Shadoobie]

I have a '79 Spider 2000 that I recently rebuilt, ignoring the head because of cost. Since the rebuild, I have had a serious problem with power even though compression is perfect and the engine cranks and drives flawlessly with new intake and carb. The only oddity in the build was that the car wouldn't run at all unless the intake cam was offset by a tooth. This offset was present before I rebuilt the engine as well. I have just removed the head for a rebuild and I was wondering if anyone had any ideas as to what is causing the offset, as I believe it is the source of the majority of my power loss. I'm currently considering new cams, but me and all of my Fiat counterparts I've spoken to are totally stumped.

[djape1977]

cam gears got mixed up at some point?

[joelittel]

Has the block ever been decked? New or old belt? Correct belt? (I believe there are a different number of teeth between the two).

Get adjustable pulleys and set the cams up to spec.

Not too long ago someone calculated that one cam tooth could be something like 6 crank degrees. Don't quote me on the number but it was something like that, ie way too many degrees.

[Shadoobie]

cam gears got mixed up at some point?

My trusted mechanic uncle believes that someone may have installed two exhaust cams, but I'm currently waiting to hear back from the machine shop on this. We definitely put the cams back in the way they came out, but, like I said, it was off before we broke the engine down.

[Shadoobie]

Has the block ever been decked? New or old belt? Correct belt? (I believe there are a different number of teeth between the two).

Get adjustable pulleys and set the cams up to spec.

Not too long ago someone calculated that one cam tooth could be something like 6 crank degrees. Don't quote me on the number but it was something like that, ie way too many degrees.

Not that we can tell, but the engine was rebuilt before I purchased the car. The belt looked practically new when I bought the car, as to its correctness I can't say. I bought a correct replacement, so I'll be sure to swap it when I put the head back on the car. I'm having the head ported and planed at the moment.

[joelittel]

Each cam pulley should have two small holes in it. One that's used to line the pulley up (TDC) with the pointers on the water neck and the other fits over the dowel on your camshaft.

If you were to draw a line from the center of the pulley through the center of the dowel pin hole and continue that line to the edge of the pulley you'd see that the holes used to lineup with the water neck pointers are offset from this line ever so slightly. One is offset to the right and the other the left. Put both your pulleys side by side, with the dowel pin holes in the 12 o'clock position and you should be able to see the difference between the two alignment hole positions.

I don't recall which is which, so I can't tell you which one is intake and which is exhaust but at least you'll be able to tell if you have two of the same.

Hope that helps

[Shadoobie]

Each cam pulley should have two small holes in it. One that's used to line the pulley up (TDC) with the pointers on the water neck and the other fits over the dowel on your camshaft.

If you were to draw a line from the center of the pulley through the center of the dowel pin hole and continue that line to the edge of the pulley you'd see that the holes used to lineup with the water neck pointers are offset from this line ever so slightly. One is offset to the right and the other the left. Put both your pulleys side by side, with the dowel pin holes in the 12 o'clock position and you should be able to see the difference between the two alignment hole positions.

I don't recall which is which, so I can't tell you which one is intake and which is exhaust but at least you'll be able to tell if you have two of the same.

Hope that helps

I'll definitely check that. However, I thought the cam gears were identical..

[124JOE]

i use to post this pic when i could but PBucket removed my pics

and i found it again

[131]

However, I thought the cam gears were identical..

Nope. As stated above, the timing marks are offset to the dowel pin hole. As per the above diagram, as the cam rotates, on the inlet cam the dowel pin leads the timing mark, on the exhaust the dowel pin lags the timing mark.

[djape1977]

remove valve covers.
rotate cams to position where lobes on first cyl just touch shims, pointing outwards. now look at timing marks. if they don't allign, someone got the pulleys mixed up.

intake is marked A
exaust and aux shaft are interchangeable, both marked S

[Shadoobie]

Thank you everyone for all of the very helpful responses, when I put the head back on (hopefully tomorrow) I'll be certain to put the cam gears back correctly. Hopefully you've saved me some serious cash on new cams!

[Shadoobie]

Just to be safe I figured I would upload some pictures of my gears to make sure they're the correct ones. The exhaust seems correct, but I'd like opinions on the intake. It doesn't have an S and it seems strangely more rusty than the other. I wonder if maybe it has been replaced at some point.

It also looks to me like the PO tried to make some marks and solve this puzzle himself.. definitely suspicious.

[djape1977]

unfortunately, these marks don't tell me anything

again, rotate cams to position where lobes on first cyl just touch shims, pointing outwards. now put the cam gears on untill you figure out which goes where. in this cams position, you should be able to get two gears with holes matching timing marks on cam housings

btw, intake and exaust cams are identical, that's why pulleys are different

[Shadoobie]

Hey guys, a little update. I've put the head back on and ensured the gears were correct, ran all of your checks, and everything seems good to go! I'm having a little trouble with distributor timing, but I'm going to wait until my new linkage collar that was swallowed by the engine gets here thanks for all the help!

[124JOE]

set the timming up to #4 not #1