Cam Timing

rebar1111 · Post by **rebar1111** » Fri Jun 30, 2017 6:06 pm

I recently replaced the cams of a 79 2L. I have not been able to obtain a satisfactory idle or performance. I suspect that the cams and/or cam sprockets have been incorrectly installed.

How can I verify that the intake cam is in the intake cam housing and exhaust is in the exhaust housing? Also that the intake sprocket is on the intake cam and exhaust is on the exhaust cam? The timing belt has been properly installed with the #1 piston at TDC and both cam sprockets at the appropriate timing mark on the sprockets.

The crank pulley has a keyway but the crank has none. I think the two are assembled using a tapered fit held in place by the 34mm crank nut. Is this true?

Help!

baltobernie · Post by **baltobernie** » Fri Jun 30, 2017 8:41 pm

Intake wheels usually have an "A" in the casting; the exhaust has an "S". Plastic wheels lack these marks. A correctly built motor can be validated by looking at the front of the engine. With the cam box pointers aligned with the holes, the dowel pin on the intake cam should be 1 o'clock to the pointer, the exhaust 11 o'clock.

I'm pretty sure the crank pulley can only be installed one way.

rebar1111 · Post by **rebar1111** » Sat Jul 01, 2017 6:12 am

OK for the sprocket position, but can the camshafts themselves be satisfactorily interchanged?
My pulley has no provision for limiting the placement except the taper and nut. (similar to taper used on a lathe)

klweimer · Post by **klweimer** » Sat Jul 01, 2017 8:38 am

I could be wrong here, but I'm pretty sure the crank needs a key to mate to the crank pulley. It's possible the key got sheared off and what's left is sitting flush with the crank shaft. My factory service manual shows a half moon key.
Kirk

rebar1111 · Post by **rebar1111** » Sat Jul 01, 2017 9:24 am

My crank has no keyway for the pulley, just the timing belt sprocket. The pulley has a keyway. It is possible that I lost a key, but there is no place on the crank for it. There are two flats @180 deg on the crank but they are too big to use as a positioner.

zachmac · Post by **zachmac** » Sat Jul 01, 2017 2:06 pm

Assuming you have a cam box mounted distributor (79 should be) and it is turning then the cams are in the right place. The exhaust cam has a drive gear for the distributor and the intake doesn't.

rebar1111 · Post by **rebar1111** » Sat Jul 01, 2017 2:57 pm

You are right. The distributor gear identifies the ex cam. It should have been obvious to me.

piperstan10 · Post by **piperstan10** » Sat Jul 01, 2017 5:14 pm

Sound like most questions have been answered. It is not clear if there is enough info to diagnose problems.

Have you adjusted valve clearance?
Checked checked the carburetor settings? Dirt in carburetor?
Checked compression
Inspected and gapped spark plugs.
Vacuum leak? On intake manifold or carb base?
Etc.

Stan

zachmac · Post by **zachmac** » Sat Jul 01, 2017 5:18 pm

I am 90 plus percent sure the crank pulley is supposed to be keyed to the crank. I thought the half moon key was long enough to engage both the timing gear and the pulley. In any case, there is a dot on the gear and a mark on the pulley that should align. Have you verified that #1 and 4 are at TDC when the pulley is lined up to zero degrees? I know mine is certainly keyed.

Follow this link: https://www.google.com/search?q=fiat+12 ... K4Hoib95CM:
Look at the third photo in the bottom row once the eight pictures load. You'll see the crank timing belt gear is installed and the key is still sticking out plenty to engage the crank pulley.

rebar1111 · Post by **rebar1111** » Sat Jul 01, 2017 8:48 pm

OK. With my glasses on, I have confirmed that the crank pulley is not tapered and that there is enough timing belt sprocket key projecting that it will properly position the crank pulley.

Thanks to all contributors.

md88plt · Post by **md88plt** » Sat Jul 08, 2017 8:59 pm

Determine TDC with crank then the cams can be set to the cam box index marks. That would be my starting point.

rebar1111 · Post by **rebar1111** » Tue Aug 08, 2017 8:40 pm

OK, I have assembled the engine according to the comments already received, and the engine may occasionally start but won't accept an acceleration.

Chilton's indicates that the intake sprocket when face from the front, should have the dowel {under the mounting bolt) located at 11:30 with the hole at 11:00 while crank is at TDC. The exhaust sprocket dowel is at 12:30 with the hole at 1:00 and crank at TDC.

Would someone please confirm what is right or what I am missing?

klweimer · Post by **klweimer** » Wed Aug 09, 2017 8:02 am

rebar1111,

I know there are pictures here on the forum showing the cam gear orientation. If you don't get a response, do some searching and I know you'll find the pictures.

Kirk

rebar1111 · Post by **rebar1111** » Fri Aug 11, 2017 6:44 pm

Just a final summary of what I have determined is factual.

1. The exhaust camshaft on a 79 2L has the distributor gear.
2. The intake sprocket sometimes has an 'A' on it. The dowel pin holding the camshaft to the sprocket is correct as shown in both Hayne's and Chilton's manual drawings. Using the dowel pin location/center attachment bolt location/ timing hole location, will determine which sprocket goes to which cam.
3. The crankshaft pulley uses part of the key for the timing belt sprocket to locate the pulley placement. Only a small portion of the key projects out from the sprocket and therefore the pulley can be jam fit into the wrong angle.

The engine is back together following the above information. Thanks to all for the encouragement.

Cam Timing

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