Assembly problem with cam

OldTee · 08-23-2008, 04:06 AM

I may have an assembly problem and could use a little advice. My right side cam may be binding. I cannot turn it by hand. I used a ratchet and cam socket to get it moving the first time and it felt smooth thru multiple 360 degrees, but still would not turn by hand. I am not strong enough to overcome the break-away tension. The left side does turn by hand. Before I take it apart and start over I thought I might get some opinions.

Some history on this engine. One of the reasons for the rebuild was a unresolved hot running condition. One bearing showed some wear, but no heat indications. The cams were reground by Camgrinder and did not show stress when removed.

cgarr · cgarr's Garage

Did it turn ok in the carrier before it was bolted down? It should turn by hand. If your case deck was not level or your head sealing surfaces were off could cause it to bind.

dtw · 08-23-2008, 06:27 AM

What engine?

Were the case deck and head deck checked? Cam carriers flat?

Back off all the cam tower fasteners and try again. If it turns then, you've got warped/uneven parts somewhere.

OldTee · 08-23-2008, 07:22 AM

Thanks, real time response here ahead of dtw advice. 79SC 3.0 w/ new p&C.

"Ok, I have loosened up the heads and it is still stiff. Further, it rotates nicely thru 270 degrees and then seems to tighten up some. I can now turn it by hand and except for this portion of the rotation seems free. Tomorrow I'm going to loosen up the cam tower nuts and see if they have any effect. I hate days like this."

cgarr · cgarr's Garage

When you get it apart and if the cam turns ok in the tower, assemble the heads to the cam carrier first, then put in the cam, if all is still ok then put the heads/carrier/cam on as a unit and tighten it down. And make sure your carrier bearings surfaces are clean, nick free and lightly oiled. What sealer are you using between the heads and carrier?

OldTee · 08-23-2008, 07:48 AM

Quote:

Originally Posted by cgarr

What sealer are you using between the heads and carrier?

Locktite 574, fresh, lightly applied.

I like your solution. May do that next.

OldTee · 08-24-2008, 09:21 AM

Success with one caveat. I loosened up the head nuts and the cam tower nuts and slowly re torqued them, testing by turning the cam as I secured the fasteners. The head nuts I torqued to 25NM followed by 33NM. The cam tower nuts I tighten to 18nm followed by 25NM. Now it turns freely except for one small area where you can feel the slightest drag.

Then a friend came over and observed what I observed, but he pulled on the cam. When pulled forward perhaps 2-3mm the cam bound up. Wear ridge in the cam tower? bent cam? bearing area hitting the tower web? something to worry about?

He left me a spare set of SC cams he had and I am debating removing my cam and inserting those for a test fit. That will tell me if it is the cam or the tower, right?

OldTee · 08-26-2008, 06:50 AM

Following up and a request for some advice.

I test fit one of the SC cams with the same results. Further examination led me to conclude the #2 web (second from the front of the engine) may be the problem. I can see thru a mirror where there was some rubbing from the previous cam. The aluminum is polished there and nowhere else. What are my options.

1. I can do nothing and figure the new steel cam will wear away any small problem with time.

2. I can hone that web and remove the slightest amount of material, then test fit and if good.... go.

3. I can remove the cam tower and have it line bored. Lawd knows where.

4. I can search out a used cam tower and hope it is in better shape than the one I have.

5. I can mortgage the house, farm, boat, airplane, wife and kids and buy a new one, even if they are available.

6. I might find I am misreading the whole situation and punt.

Option 2 appeals to me.

Comments.

MatthewBrum · 08-26-2008, 07:08 AM

Make sure when you rotate the cam that it is in the axial position where it would be when the sprocket and shims are on and tight. it is easy to push the cam forward and rub the large plug on the other end of the cam bore.

My SC has a little tight spot when rotating by hand. If you can put a wrench on it and it feels fine, I'm not sure if I would worry about it. But in the end it depends on how it feels to you.

cgarr · cgarr's Garage

You could dye the bores, turn the cam and look for the bad spot, you might just be able to polish it out. Can you turn it by hand or only with a wrench past the one spot? Normally I would check it on my surface plate to see if it was twisted or warped but since it did not change when it was bolted up it may not be.

OldTee · 08-26-2008, 07:48 AM

Thanks, I can turn the cam smoothly thru 270 degrees and then with about 2 or 3 lbs of additional pressure move smoothly over the one spot by hand. I may try to dress out the shiny spot by hand. I can just reach it.

WERK I · WERK I's Garage

Have you tried placing the other side's cam into that suspect tower?

304065 · 08-26-2008, 08:58 AM

WHY is the cam binding?

Remove the cam tower and check that the top surface of the cylinder heads are level. If you have one that is lower than the other, the cam tower will warp, causing the binding.

If your heads have been resurfaced, perhaps too much material was taken off, which could account for the difference in height. You can use a feeler gauge to measure how much one or more are off.

Next: Is the cam tower base flat? Same drill-straightedge and feeler gauge, there should be absoutely no clearance between one end and the other.

Probably what is happening is the cam tower is distorting as you torque everything down due to a high spot. If the cam didn't bind before, it's unlikely that a distortion SPECIFIC to the bore itself is the problem.

356RS · 356RS's Garage

If the cam turns smoothly 270 degrees and then gets tight, it sounds more like a cam problem. If the cam tower is uneven or something why would the cam only bind in one spot?

304065 · 08-26-2008, 09:25 AM

A fair point, certainly there must be a high spot on the cam that is dragging on a high spot in the housing. Which is more likely, growth of the camshaft or distortion of the bore under torque?

I suppose some PO could have gouged the bore with a lobe when "stabbing" in the cam, but first things first.

WERK I · WERK I's Garage

Quote:

Originally Posted by john_cramer

A fair point, certainly there must be a high spot on the cam that is dragging on a high spot in the housing.

+1 on the cam being suspect.

dtw · 08-26-2008, 09:45 AM

Did you ever relieve all torque on the tower and try to turn the cam? At this point, I'd pull the cam tower off the engine and test it on the workbench. See my prior notes though, binding cams are frequently an indicator of an uneven deck. This can be an issue with the case, cylinders, heads, or all of the above. If the cam turns freely on the bench, you have issues with another component(s). Relieving the tower journal won't fix that.

OldTee · 08-27-2008, 07:50 AM

Ok, removed the cam tower. It is neat how easy it is to remove the Loctite when it is new. A good use for moonshine maybe. Pics show how I did the test. I could not get a .015mm under the ruler. I put the cam in the tower and it still has a little resistance at one spot. I pulled the cam out and tested each journal (I guess that is what you call it) and found the #2 to have drag. So, to the hone for some gentle polishing.

911pcars · 08-27-2008, 11:52 AM

It sounds like you've tried the methods suggested for assembling alloy engine parts. As suggested by others, check the cam for straightness first. If straight, proceed to the next step. Making allowances for a bent cam is not suggested for longevity. The components in each "stack" on each bank must be identical to arrive at an identical cylinder/cylinder head clamping force.

Install the other cam in the housing and see if the symptom is the same. Bent or distorted housing? I would think a used housing in good condition would be cheaper than sleeving, then remachining a crooked bore.

Sherwood

OldTee · 08-27-2008, 11:55 AM

Fixed it. Took the cam and tower to Matt DeMaria, Stuttgart Performance Engineering and he patiently selectively filed and polished the cam until it turns smooth as butter with two fingers. Matt suggested that the cam was in fact bent, but they all are, somewhat. Mine, he said, was not bad at all.

Matt runs a one man shop outside Washington DC in Gaithersburg, Maryland. (301) 948-6762. He is the guy we go to when we are looking for expert advice. I should have gone there first and not taken up so much electronic space here.