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Message started by DragBikeMike on 12/15/18 at 17:25:37

Title: Head Cover Alignment
Post by DragBikeMike on 12/15/18 at 17:25:37

In October, I bought a good used cylinder head on eBay. I wanted a head to practice porting. At the time, I didn’t buy the associated head cover (either because it wasn’t offered on the auction, or I didn’t have the sense to buy it). Later, I purchased a head cover on eBay to use as a test bed for cam timing checks. I figured I could clean it up and install some fresh rocker arms, then use it on my ported head.

Last week, I was looking at the parts fiche and noticed the head and head cover are sold as an assembly. My heart sank. How could I have been so stupid? Of course, the head and cover are sold as an assembly because they use blind dowels. When they manufacture the head assembly, they lay out the dowels, assemble the head & cover, and then bore the bearings for the cam. That way the dowels will always maintain alignment between the upper and lower halves of the bearings.

I immediately tried to assemble the head and cover with a cam inside to see if I might have gotten lucky. No chance. When the cover was installed the cam would not rotate. Too bad for me.

I pondered the problem for awhile and decided to try and establish correct alignment and re-dowel the components. The process worked pretty good and it’s not too difficult, so if you’ve got a mismatched head & head cover, all is not lost.

Title: Re: Head Cover Alignment
Post by DragBikeMike on 12/15/18 at 17:27:54

First you must remove the existing dowels. Then come up with two alignment fixtures that are .0015” to .0020” larger than the cam journals. I call these fixtures “spuds”.

I rooted through my junk box and found an old wrist pin (I believe its from a mopar 318). The wrist pin is .9843” diameter (.0014” larger than my RH cam journal, good enough). That was pure luck. I didn’t have to make a special alignment spud for the RH cam bearing.

I found a small piece of bronze stock that was large enough to make a spud for the LH cam bearing. I machined that to .7877” (.0015” larger than my LH cam journal). Ready to rock & roll.

Here’s what the alignment spuds look like.

Title: Re: Head Cover Alignment
Post by DragBikeMike on 12/15/18 at 17:29:01

With the stock dowels removed, place the alignment spuds in the head and install the head cover. Tighten down the bolts and verify that the RH spud locks in place. That will insure that the upper & lower halves of the cam bearing are aligned fore & aft. Look at the joint between the head and head cover, it should be fully closed.

Install the spuds like this.

Title: Re: Head Cover Alignment
Post by DragBikeMike on 12/15/18 at 17:31:12

Then put the head cover in place, shift it right or left to bring the upper & lower faces of the hole in the RH side flush, and tighten down the hardware. You should not be able to turn the RH spud, the joint should close fully, and the faces of the cover and head in way of the large hole on the RH side should be reasonably flush. If you can turn the spud, you need a slightly larger spud (maybe .0005” to .0010” larger).

Now that the head cover is installed and locked down in correct alignment with the head, drill and ream new dowel holes.

I chose the holes marked “A” & “B” on this sketch.

Title: Re: Head Cover Alignment
Post by DragBikeMike on 12/15/18 at 17:32:30

Hole “A” is the location of an existing dowel. Hole “B” is a new location. Neither hole utilizes a sealing washer, so they are not holes typically subjected to oil pressure. You are ready to drill and ream. This operation requires a drill press. I don’t suggest trying to do this with a hand drill. Double and triple check the dimensions I provide. Your parts may be slightly different, you don’t want to ruin them. The goal is to end up with a reamed hole that goes all the way through the head cover, and about .250” into the head. Drill hole “A” with a 23/64” drill to a depth of 1.86”, then ream with a .374” machine reamer to a depth of 1.86”. Drill hole “B” with a 23/64” drill to a depth of 1.26”, then ream with a .374” machine reamer.

Here’s what hole “A” looks like after its finished.

Title: Re: Head Cover Alignment
Post by DragBikeMike on 12/15/18 at 17:33:24

Here’s what hole “B” looks like.

Title: Re: Head Cover Alignment
Post by DragBikeMike on 12/15/18 at 17:34:16

Here’s a shot of a typical hole once the cover is removed.

Title: Re: Head Cover Alignment
Post by DragBikeMike on 12/15/18 at 17:35:29

I’m a lazy sort of guy. I try to avoid machining parts if I can buy something that will work OK. A quick trip to the local hardware store was in order. I managed to find some bronze bushings with a .3755” OD. They looked like they would probably work, and if they were too tight, I could always buzz them down a bit with some 320 wet & dry. They fit perfectly. A light drive fit. A testament to how sloppy my old jalopy 3-in-1 machine is getting. Can’t even ream a hole to proper size. Any accurately sized sleeve or bushing will do. You want a dowel ½” long with a .3750” to .3755” OD and a .250” ID. Cut off two chunks ½” long and apply a slight chamfer on each end. Then install the dowels in the head at locations “A” & “B”. You want a light drive or push fit with no play.

Here’s a shot of one of the bronze bushings and a finished dowel.

Title: Re: Head Cover Alignment
Post by DragBikeMike on 12/15/18 at 17:36:38

Here’s what a dowel looked like installed.

Title: Re: Head Cover Alignment
Post by DragBikeMike on 12/15/18 at 17:41:34

Install the cam & cover along with a little assembly lube on the cam journals. With the hardware tight, the cam should rotate freely. Mine was like a greased pig. Not even a hint of binding.

You could probably leave out the existing large dowel located in the oil feed hole, but there’s risk of the O-ring getting into the feed hole. The dowel captures the O-ring and helps to keep it in place. If you reinstall the old dowel as-is, it will prevent the head cover from being installed because the two new dowels position the cover in a new location. Reduce the top half of the existing dowel to .412” diameter. That way, it still has a drive fit into the cylinder head but has lots of clearance with the hole in the head cover, which allows the cover to fit nicely over the new dowels. You don’t want to go much less than .412” and risk the dowel migrating up into the .390” hole in the cover, which would cut off oil to the cam bearings.

Drilling and reaming the hole at location “B” results in the loss of about 6 internal threads. I used a 6mm x 1mm tap to cut two additional threads. A longer bolt will be required to take advantage of those two new threads. Tightening this bolt will be a delicate task and you will need to remain aware of the lack of full thread engagement. But going easy on the torque at hole “B” should not present any major problems. You just have to pay attention to it. If you yank the threads out, drill straight through and install a nut on the underside, adjacent to the intake manifold.

I know my choice of bronze dowels isn’t the best. Really should be steel. But as I said, I’m basically lazy. This is not a component that gets removed and replaced often. The bronze should serve well.

This realignment process has worked out pretty well……so far. The proof is always in the pudding. I’ll have to run the assembly on an engine to be positive that the operation was a success. For now, the future looks bright.

Title: Re: Head Cover Alignment
Post by justin_o_guy2 on 12/15/18 at 22:00:26

GOing out on a limb here, but I doubt there is a dealership in the country where so many problems with a savage can be solved.

Title: Re: Head Cover Alignment
Post by Dave on 12/16/18 at 03:56:12

Yep........every time I see an eBay seller who has split the matched set and is selling the cylinder head cover separate from the cylinder head - I want to email them a good scolding.

Good job reconciling the irreconcilable differences!

Title: Re: Head Cover Alignment
Post by batman on 12/16/18 at 18:06:35

Going to have to start calling you "Super Mike" !

Title: Re: Head Cover Alignment
Post by Armen on 12/23/18 at 06:17:09

Wow!
Thanks for documenting all your hard work.
Since the head and cover are line bored together, along with side to side misalignment when swapping covers, there is also a chance of a change in up and down clearance. Too much and the cam will wiggle, too little and oiling disappears. I know you said the cam spins freely, but it might be worth a look.
Perhaps use some Plasti-Gauge and measure the up and down clearance of the cam in the journal?
I've had some grief with mix-and match heads and cam caps, as well as heads and covers in the past. PITA, to be sure.
I could bore you with some stories...

Title: Re: Head Cover Alignment
Post by Serowbot on 12/23/18 at 08:21:52

I could do that... ...not... :-?

Title: Re: Head Cover Alignment
Post by DragBikeMike on 12/23/18 at 20:24:03

You are absolutely correct Armen. I have been meaning to get some plasti- gauge and give the vertical clearance a look, but the holiday season has presented too many distractions. Once the holiday dust settles, I will be taking that reading.

The vertical alignment would be pretty tough to fix. I used to work with a product called "Artis Shim Stock" (sic). It's a plastic shim material that came in a variety of thicknesses. That might be a possible solution but maintenance would be a total pain. Another possibility might be brush plating, but it would take forever and also empty your wallet Big Time.

I suspect that too much vertical clearance would be fairly simple to correct (skim cut the bottom of the cover), but too little vertical clearance would be very difficult to fix. I'll take the pasti-gauge reading and post the results.

Title: Re: Head Cover Alignment
Post by Armen on 12/23/18 at 21:40:39

OK, the stories:
I had a '79 XL250S. Needed major top end surgery. It also had a bad leak between the head and valve cover. I decided to lap the top of the head and the bottom of the cover. Had to do a lot of lapping before I saw that both surfaces were flat.
Bike started right up, and ran for seconds before going SQUEAK! and stalling I had wiped out the clearance, and no oil was getting to the cam journals.
Took it apart and started with coarse lapping compound, then fine compound, then aluminum polish, repeatedly checking the clearance, then hosed it forever with contact cleaner.
SUCH a pain in the butt.
Another time a customer had lost one of the cam caps on a GS750. Found a used one and had to do the same voodoo to it.
Probably impregnated the metal with some abrasives.
woof.

Title: Re: Head Cover Alignment
Post by DragBikeMike on 12/24/18 at 13:22:11

I imagine I should have at least .001" vertical clearance since the spud was around .0015" larger than the cam journals and the cover went home without any trouble. Anyone know what the actual specification is for the clearance? Shazam! I see the all-inclusive Clymer Manual calls it out at .0013" to .0026" with a wear limit of .0059". Now I've got something to shoot for.

Title: Re: Head Cover Alignment
Post by DragBikeMike on 01/26/19 at 19:05:20

Finally got around to measuring the vertical clearance with plasti-gage. I've got .002" on the right journal and .0015" on the left. Good call Armen. Probably would have been a good idea to check that before I embarked on the realignment. I got lucky this time.

Title: Re: Head Cover Alignment
Post by DragBikeMike on 06/06/19 at 20:18:08

I unearthed this old post to report how the realignment worked. I've put about 160 miles of hard running on the realigned cover and it is working just fine. I've run it up to 7K at least four or five times and also did quite a bit of freeway riding. No hiccups. I think it's safe to report that this realignment procedure works good.

If you can't find a matched set (head & head cover), you can buy the cover or the head individually and realign them using this procedure.