cam suggestions

[MmmBoost]

i wanted to post this thread for a few reasons. I have an upper end knock, caused by too much wear in the cams, even though my lifter shims are very close to being within specs, it still knocks a lot.

i grabbed a set of good cams from the junkyard (n/a motor) and here is what they looked like:

notice the normal wear on the babbit material that usually scares most people. you can definitely tell that it is a soft material, and if you can feel grooves in the metal, the cam is bad.

i took the cams to my machinist and had him micropolish the journals. i then removed the oil coking from the lobes with a die-grinder with a scotch brite pad attatchment.

results:

as you can see, the cams were fine, before and after, all journals measure within spec according to the tsrm.


as a second note, when i took apart my top end, i discovered what had been causing the knock, and the oil leak that i had at the front of the block.

this wear was caused by the previous cams being scored (really scored, not just the babbit coating). i had re-used these cams and over tightened the timing belt. note: timing belt tension is automatically set by the spring on the tensioner. i had pried the tensioner pulley to tighten the belt and then tightened it. oops.


all in all, now the head needs to be replaced, so don't let this happen to you. the cams and cam journals in the head are often overlooked, but are very important.

 

[Adjuster]

Yep, you don't want to tighten up the belt too much, that's for sure.

I'm not sure there is babbit on the cams, but your right that most people freak out over any scoring on the cam journals when they don't need to.

The cam saddles/bearings are just machined alluminum of the head. Nothing more, nothing less. I've coated mine with good success with molydisulfied, but you have to clean up the head many times as you need to sand blast the bearing surfaces to then coat them with moly....

I also think it restores the clearance somewhat too. (The coating.) Nice find and clean up on those NA cams, too bad your head was screwed up. Nice post on why not to overtighten your cam belt too much. (I actually add a few extra pounds of tension on mine over the spring, but not so much that it's going to cause excess wear of the front cap cam journals like you've got there.)

Another thing that might have caused this. (Check your rear cam caps for wear, I bet they are worn out too...)

Here is what happens.
Your head is milled for a gasket, but it was warped to start with. When they mill the head, they cut the deck surface flat, but the warped condition takes material off the ends more than the middle. (With respect tot he cam bores.) Then when you bolt the head onto your block, you pull the head down flat onto the new gasket, and the cam bores are now "WARPED" this causes the cam to flex as it's turned, and generally, will cause the front and rear cams bearings to wear more than the middle ones. This is an issue as the cam is lubricated from the front cap, and excess clearance there results in less oil going to the rest of the bearings, causing even more wear...

Just for shits and giggles, check your head with a straight edge, and you might find the deck is flat, but the cam bores are warped...

I have read of people cracking cams as a result of this on extremely warped heads, milled flat, but turning the cam bores into torture racks for the cams. (Mostly on I6 engines is this a problem, but I4's can have it too.)

Easy to resolve. You need a machine shop with a oven designed to straighten heads before they are machined.

What they do is clamp a warped head onto a microflat steel table in the oven, pulling any warped condition out of the head. Then they heat up the head to 700f for a few hours, and let it cool down while clamped to the microflat surface. This straightens out the head. After it's removed from the oven, it's checked for being warped again, and if it's straight, then it's milled for the deck surface. This keeps the cam saddles straight to the deck surface, and limits cam bearing wear.

Some say the process destroys any heat treatment the head might have had from the factory, but I've seen it done to some pretty high dollar heads with thousands in port/valve work, and they work fine in racing engines, and street motors.. If I could afford a brand new head, that would be great, but I can't, so a straight one is a better place to start than a warped one machined flat with screwed up cam bores.

 

[suprarich]

You can also have the cam bores "line bored" to solve the cam run-out from milling a warped head. Your machinist will need a head torque plate to do this so that the head is pulled into a "installed" state. This whole process will square the cams to the gasket surface.

 

[Adjuster]

Problem with the line bore is it increases the bore diameter.. more oil space is lost pressure..

I could see doing the line bore, then coating the saddles/caps with molydisulfied to restore the bore dimension.

Seriously, they are just soft cast aluminum, and any time the cam journal has metal to metal contact, the cam is going to win. (Thus the reason every cam I've seen taken out has aluminum deposited all around it, the "scoreing" everyone talks about, or calls babbit material.)

Also, keep in mind, this design works fine, and is used in this motor to many hundreds of thousands of miles, and in other motors with similar results. The cam is fed pressureized oil at the front cap, then oil goes down the cam, and pressure feeds every journal all along the head. Just make sure your cam is clean inside since you do not want any abrasive material inside your cam, forced into the close tolerance between the cam and the head...

 

[IJ.]

If you're line boring/honing the Cam tunnels you need to mill xx from the caps faces then offset the boring bar xx towards the deck surface, this way you end up with round straight smooth tunnels the correct size.

 

[suprarich]

Another thing about line boring too worth mentioning, is that you can size the tunnel to match the cams you will install. You will also need to reshim the cams after a line bore since material is removed from the head portion of the saddle, the cams will be "closer" to the old shims.

 

[Adjuster]

Personally, I would think that the cost of line boring the cams, would exceed the cost of a good used head and cams..

Just a thought.

 

[MmmBoost]

i was going to have my new head line bored (even though it looked pretty good already) and they were going to charge me $200.

however, since the mk3 head is closed off at the rear, they told me that their boring machine needed to poke all the way thru and move back and forth. so what they did (for a lot cheaper) was hand file the caps down a bit and use an arbor to manually hone each bore to the respective cam journal. i just checked tonight and all the journals are within 0.025 to 0.045mm which is a little bit tighter than stock. and the cam still turns freely. hopefully this will help some of my oil pressure issues, and insure that this motor can turn many more miles before the next rebuild.