Installed used cam - now I have no compression. Please help

[Joe Stewart]

This is a mid '80s 1.6 liter naturally aspirated diesel engine. It has the hydraulic lifters.

I was going to adjust the injection timing this morning. I had trouble getting the cam sprocket loosened. Should have used a puller, but like an idiot, I gave it a good rap with a hammer, using an old timing belt as a cushion. I ended up breaking the cam.

I checked my parts boxes and found a couple of old cams. All of my parts came from early to mid '80s diesel rabbits and jettas, so I was pretty sure these cams would work. They "looked the same" as the one I broke.

Anyway, I installed it and got all the timing marks lined up. Adjusted plunger depth. All of that went fine. When I turned the ignition key to start it, the motor spins freely, almost like the injectors were removed. Virtually no resistence. No firing. No smoke out the tail pipe. Can't figure it out.

I checked and found that all of the earlier vw diesel cams are the same, from '70s up to the '90s? Doesn't matter if its naturally aspirated or turbo, mechanical or hydraulic lifter.

so now my Jetta is dead in the driveway. Any ideas guys? This car ran fine yesterday and has ran fine for the last year.

Thanks

[82vdub]

While I don't know the factural answer to this as I type, my first guess would be that a hydraulic cam and mechanical cam don't have the same base circle. In other words, they aren't the same cam. The base circle of the cam is the part of the lifter lobe where the lifter rides on when it's not opening up the valve. I'm guessing that the hydraulic cam has a larger base circle, and when used in a mechanical block, it holds all the valves open so that they won't close. I'd tell you to stick a feeler gauge in between the cam and lifter, but I think hydraulic has a slight interferrence fit, which would mean that there is no space. So I'm kind of stuck on what to tell you.

If you have access to a micrometer, measure the base circle diameter from your old hydraulic cam and compare that to a mechanical lifter cam and see if they are the same. We're talking a couple tens of thousands here of difference can hold the valves open.

[TylerDurden]

How long after installing the new cam did you try to start the engine?

Caution-
After installing new cam followers, the engine should not be started for at least thirty minutes. New cam followers are at full height and must be allowed to bleed down to their proper height. Failure to do so this may cause valve or piston damage.

[Joe Stewart]

OK, thanks for the replies.

I measured the base circle and lobe height on the two cams involved and they both appeared similar. But I'm using a plastic micrometer, and I would not be able to tell if it was only a few thousandths difference.

I'm going to try to slip a feeler gauge under the lobes - won't be able to do that until saturday.

I had waited about 1-1/2 hours after I installed the used cam before I tried to start it up. This is how long it took me to line up the timing marks - I'm slow.

If all else fails, I have two more used cams to try.

[82vdub]

The plastic style will get you in the ballpark, but to know for sure, you'll need to use a real micrometer. Remember to use a wrench on the crank bolt to turn the engine over by hand at least two revolutions before using the key. This is in case you mess up the cam/crank timing and by using manual labor instead of the starter, you won't bend valves when they hit the pistons.

[Joe Stewart]

OK, thanks for all the replies. Here's the follow up:

I had reached the end of my rope with this cylinder head, so I took it off and brought it to the local head shop.

The technician told me that three (3) of the lifters were stuck and were not decompressing. He said he put one or more of them in a vice for a couple of days and he could not get them to go back down.

He replaced three of the lifters and he says that now I'm good to go.

I have no clue as to WHY these lifters chose this time to go bad. Perhaps removing the cam had something to do with it?

I started to install the cylinder head today. Will finish next weekend.

Thanks again.

[Prairieview]

The problem you are describing (with the stuck lifters) is EXACTLY what running a solid lifter camshaft in a hydro head will do over time (roughly 15,000 miles or so). The heel of the cam keeps the lifters partially compressed and over time they freeze up. Zip-bang. Continuing to run it will result in the tops of the lifters beginning to flake off and settle into the bottom of the oil pan.

I know because I did it.

Edit: you NEED to find a true hydro camshaft (which is not flaking) and those are getting hard to come by. Many of them will have an "L" stamped on the #1 cylinder end between the lobes. Some of them do not have the "L." I have three of them which I KNOW are hydro cams and they all have the "L."

I can not imagine finding a good hydro camshaft for less than $50 nowdays. I just bought one for $35 and had to pay like $15 for freight.