So, this completes Part 3.  The mods described above have been working fine on my Stage II head for the last 4600 miles or so.  No unusual noise.  Valve clearance checks have been fine.  Oil pressure did not change when I drilled the oiling hole for the intake rocker shaft.  Cam lobes look great.  I think these mods improve oiling to some critical areas and should add a little longevity to the valve train.  The heavier springs and high-lift cam will certainly take their toll on valve train life expectancy.  It goes with the territory.  Ya wanna play ya gotta pay.

I hope you find this report informative.  As always, I welcome your questions & comments.  Knowledge is power.

Best regards,

Mike

A forum member brought something to my attention regarding the modifications outlined in this post.

“In your new article you posted, you mentioned drilling the cam lobes for oil holes – you did not mention drilling the center of the cam to make the interior hole the same size as the LS650.”

The member went on to explain:

“I believe the center hole allows oil to pass to the cam chain, and that the DR650 has a smaller hole to limit the oil flow to the cam, and it uses a smaller hole as there may be higher pressure since there are no holes in the cam lobes.  The LS650 needs a bigger hole so the lower pressure oil can flow.”

I am embarrassed to admit that I did not take that hole into consideration.  It’s an important part of the system and I should have been looking at it, especially since I’ve seen it discussed a number of times on this forum.

This is the hole in question.  The stock DR cam is on the left (.060” hole) and the stock LS cam is on the right (.079” hole).

So, I was waaaaay screwy-wrong about that oil cooler feed.  I figured the cooler circuit was handling “unpressurized drain oil” from the head to the sump.  It is actually handling “pressurized cooling oil”.  Oooooops!  That’s a pretty big screw up on my part.  I’m not worthy.  

It was time to put that cylinder head under scrutiny.  The oil flows through the stock LS650 camshaft as shown in this picture.  Please forgive my sloppy arrows.  The stock DR cam doesn’t have holes in the lobes so internal pressure will be higher and the center hole can be smaller.  The thought here is that if you put the holes in the lobes of a DR cam the internal pressure will go down.  If you want to keep the flow the same out the right side of the cam then you need to enlarge the center hole.

The oil that exits the right side of the camshaft fills a small reservoir adjacent to the steady bearing.  That reservoir of oil keeps the steady bearing wetted with oil.  The steady bearing can’t be pressure fed because it’s only half a bearing.  It serves as a cradle to steady the camshaft during the compression stroke.  During compression both valves are closed and the drive chain pulling down on the right side of the cam will load up the steady bearing.

This is the steady bearing.  The oil reservoir is circled in red.

Let’s zero in on that cam bearing.  Yep, zero oil.  It’s wiped.  Look at how the aluminum is smeared.

I’m still unsure which is better.  Should you enlarge the center hole on a DR650 cam, or leave it as is?  If you enlarge the hole, it will agree with the LS650 design.  I suspect it will increase oil flow through the cam and provide more oil to the steady bearing.  But if you leave the oil hole alone, it will increase oil flow through the cam lobes and provide additional lubrication to the rocker arms.  The rocker arms certainly are subjected to higher loads, especially now with the heavy valve springs and aggressive cam profile.

Using the HammerHead as an example, it appears as if the steady bearing is pretty forgiving.  Looks to me like it can get by just fine on the oil available through the smaller hole in the DR cam.  Up to this point, I haven’t had any problems with the steady bearing.  But there’s a flaw in that mindset.  I don’t know if I have ever run a cam with holes in the cam lobes and the smaller (.060”) hole in the center of the cam.

I have run a stock DR cam with the stock DR center hole and no holes in the lobes.  That worked fine for a long time.

I have run two Web cams intended for the DR650.  I drilled holes in the lobes of both those cams, but I didn’t even look at the center holes other than to make sure they weren’t plugged.  Since I provided Web with LS cores, I might possibly have the larger holes in those Web cams.  It’s also possible that they sent me cams made from DR cores.  I never checked.

This is where the forum comes into play.  Do any of you have experience with running a DR cam with holes drilled in the lobes and the standard .060” center hole?  If so, any problems with that setup?

I've been running the DR cam for about a year now. The hole in the center of the cam was drilled out to .080  No other holes were drilled anywhere. The engine is stock, except for the carb and muffler. Runs great. No strange noise or vibration . Shell T6 syn. Next time I get the cover off, I will inspect it carefully. I have a feeling that I will see everything fine.