Valve gap off tdc

[nic]

Hi All,

I've got a issue with a new engine i'm building.

I've set the valve gap correct at TDC but when i turn the engine over so its firing on a different cylinder i have a very large valve gap.

If i was running the engine i'm sure this will make heck of a noise.

Has anyone seen this before??



2332cc comp 9:1 running 041 mofoco heads duel springs FK8 cam.

[turbobaja]

Cam timing has to be off for that much gap to be present off TDC on compression stroke. Are you sure your checking the right cylinder? How was the orientation of the slot on your cam with the dot on the gear when installed? Adjustable gear? I'd pull the oil pump and have a look to be sure

[Marc]

Karl's advice is good.

...although you can't see the cam & crank gear timing marks through the oil pump hole you can infer their position since the oil pump drive slot points at the one on the cam gear and the pulley woodruff key is 180° from the two on the crank gear. When the engine is set to #1TDC ready-to-fire, the woodruff key should be at 9:00 - rotate the crank 90° clockwise from there to put the woodruff key at 12:00 and the slot in the cam should be exactly vertical (actually you don't even need to remove the pump to check this, only the pump drive gear). On a 3-rivet cam, if it's off by 120°, the gear is bolted to the cam incorrectly - that can be remedied without splitting the case by working through the pump hole. If it's off by any amount other than 120°, it's teardown time.

[nic]

I sure the cam gear is correct the cam dot is between the crank two dots and the slot points at the one dot on the cam gear.

I will double check it tonight though

The pictures above are from cylinder 4 when the engine is TDC on cylinder 1.

I think the rockers should be just touching the valves but not moving on 4 has just finished the exhaust stroke.

[The Newf]

Possibly you're not on the correct cylinder when you're adjusting the valves???Go by valve overlap method:turn engine until the timing marks indicate tdc.Rock engine cw/ccw while observing valve movement on cylinders 1 & 3.If cylinder 3 valves are "rocking" (open/close),you're on cylinder 1.Conversly would put you on cylinder 3. Go from there.

[turbobaja]

This would be a good opportunity to learn to "degree" your cam. Grab your cam spec sheet that hopefully came with your cam, or you can find one for your K8 online I'm sure. Print out a 360deg pulley cover from the interwebs if you don't already have a 360deg pulley on the engine. Start with a piston stop so you can find TRUE TDC so you know exactly where to tape your printed degree wheel, or see how accurate your crank pulley is marked. Then get a dial indicator setup directly on the end of a pushrod on #1 and start rolling the motor over. See if the numbers on your cam card match your crank position for .050" lift up and down the cam ramps. This is part of blueprinting the Short block so you know the cam you think you have installed is actually the cam you wanted to buy. And you'll have a better idea of what to expect from the cam once it's up and running, weather you've got it advanced or retarded from the card due to your gear or the way it's ground. Check all 4 lobes (only need to check @ 2 cylinders on same head, other 2 cylinders are using same 4 lobes, etc.).

[nic]

This is the cam on TDC No1

[The Newf]

This is the cam on TDC No1

Read Marcs post.
You can use my method without removing the oil pump.

[Piledriver]

There have been runs of improperly ground cams from time to time, but you must be able to degree the cam etc (per above posts) to determine if that is really the issue.

[Marc]

When properly assembled the cam gear dot is in line with the pump slot and one of the bolts - assuming that part's correct, it looks as though you're on #3, not #1, in the photo above.

The woodruff key is at 9:00 when at TDC #1 OR TDC #3 since the cam turns at ½ crankshaft speed.

From TDC #1, when you rotate the crank 90° CW the cam will turn 45° CCW, so you end up with the woodruff key at 12:00 (crank gear dots at 6:00), and the pump slot vertical with one bolt (and the cam gear dot) at 12:00.

Looking at the picture provided, rotating the crank 90° CW is going to put the slot vertical OK, but the bolt/cam gear dot would be at 6:00 => that ain't TDC #1 in the picture.

[Marc]

One other tidbit - since the "companion" cylinders on opposite sides of the engine (#1 & 3, #2 & 4) have their valves actuated by the same cam lobes, another check you can make is to rotate the crank until any given valve is at max lift, at which point the "heel" of the cam is being offered up to the opposite valve, and setting the lash on the latter at that point. This is the basis of the "eight-step" valve adjustment procedure favored by some VW mechanics...normally it doesn't make a whole lot of difference compared to the "four-step" method unless a cam has extremely long clearance ramps, but it's still a valid way to double-check.

[Dougy Dee]

Did the OP get this sorted?

[Chip Birks]

I have seen this exact behavior on a cam in the past. Drove me crazy. Honestly I never figured it out, I just changed the cam. It got a little better. The first cam would see over .015 lash when another cylinder was at the tdc with both valves closed point. I could make every valve do it at some point. It was super bizarre and nobody could explain it then either.

I switched cam manufacturers after that. Although, I have come back to the same builder again.

I didn't realize the cam had this behavior until after the car had been on the road for months. It ran REALLY good, but was clackity.