Cam Lobe / Shim Wear Marks, revisited

[Yamaha V6]

A while back, the topic was brought up about the actual contact area of a cam lobe against the shim surface. I snapped a pic last night during the Stage 2 cam install:

As you can see, the lobe does make a significant contact path across the entire shim surface; in fact, that's why the sizes stop at 2.000; anything thinner, and the cam lobe impacts the shim bucket itself (especially the notch for picking out the shim). Also interesting was on using a new Kawi shim, it left oil / contact patch marks across the entire shim. It was neat to see the contact area on hand-spinning the cam.

What I didn't like seeing was the up-to-2900 size shims in there already. This was on the engine that SHO Shop built for me a couple of years ago. There was also NO intake porting on their "ported" heads.

Also, here's the heads, buildup-wise:

 

[poissonverte]

So you paid for ported heads, and didnt get it?? ouch. rant

 

[shojuan]

Yamaha V6:
What I didn't like seeing was the up-to-2900 size shims in there already. [/IMG]

This is why I would like to see someone get the ball rolling for production of BRAND NEW billet ground cams! It would be a little more expensive, but those regrinds are awfully expensive for what they are: REGRINDS! Maybe when I'm on more solid financial ground I'll look into getting the ball rolling on this one. Somebody needs to step up to the plate and well, I see the need so it may as well be me if nobody else. Lol, just need that 100k/year job first!

I never had any doubts about the cam lobe making contact with a major portion of the shim. Sometimes Scott does indeed get things wrong. Scott, you gotta admit that you don't know EVERYTHING, bro. Although it's hard to imagine that you could be any more well respected, I'm sure with an occasional gesture of humility there would be a few more whose respect for you would grow. thumb

 

[sdpatt]

shojuan:
Sometimes Scott does indeed get things wrong. Scott, you gotta admit that you don't know EVERYTHING, bro. Although it's hard to imagine that you could be any more well respected, I'm sure with an occasional gesture of humility there would be a few more whose respect for you would grow. thumb

I have been wrong before and I will be wrong again.

All I know is that the wear area on all of the shims I have seen with my own eyes (a few) exhibit a contact area no greater than the center 10-12 mm circle.

You can see that the ramp of the cam lobe is not a flat surface and the resulting contact area is therefore only a thin line the width of the lobe. I see a visible air gap under the outer 8 mm or so of the shim due to this curvature.

That's what I can see with my eyes. Slide a thin feeler gauge under the gap and see how far it goes. I'll bet with an infinitely thin gauge the gap goes all the way to the wear area in the middle of the shim. Also, since the tappet rotates, any "wear" patterns other than perfectly circular on the shim could not be caused by the motion of the cam lobe.

The design of the SHO's or any other direct acting mechanical bucket (DAMB) valve train could not be allowed to apply a significantly non-centered force to the tappet. A force out of line with the direction of motion of the valve stem and tappet would result in rapid wear within the tappet bore and possibly excessive friction and jamming of the tappet. That would not be an acceptable design for a high velocity valve train mechanism.

Sorry. I know what I have seen.

 

[Yamaha V6]

Picture, for a second, the bucket NOT rotating for a few revs. It happens Scott. The rest of us see buckets that apparently have "stuck" in a fixed position for X time period, leaving a cam lobe wide wear mark in addition to the typical circular darker center area you're talking about. Also, you'll get a "groove" wear circle close to the outside diameter of the shim as well (when things are moving freely).

Agreed, imapct forces are supposed to "smoothed" out with the profile of the cam. Just as you stated, Sorry, I know what I have seen.

 

[shojuan]

Lol, you two are great! Gotta love having you both here hehe.

Fred, how many years has it been since you bought those heads? If the statute of limitations hasn't run out you should consider seeking a remedy for the lack of porting. Monies were paid and services were not rendered. If somebody takes a dump on that one it shouldn't be you.

 

[srfdude]

I just did a quick AutoCad sim/drawing of a couple different SHO cam profiles. They clearly show the total width of the shim is used, although no doubt the pressure/load is greatest as you get toward the center. I can send a small GIF if anyone wants to see what they look like.
Mike

<small>[ June 12, 2003, 12:54 AM: Message edited by: srfdude ]</small>

 

[MeShoHorny]

Rick, are you sniffing glue again? Do you have any idea how much NEW Billet cams would cost!?!?!?! And people think $500 for staged cams is expensive!

Throw out a number, I need a good laughing today

 

[shojuan]

MeShoHorny:
Rick, are you sniffing glue again? Do you have any idea how much NEW Billet cams would cost!?!?!?! And people think $500 for staged cams is expensive!

Throw out a number, I need a good laughing today

I know how much they cost for Porsches. Just double that number and use it for a baseline of how cheap they *could* be if enough people lined up to buy them. The market for new billet cams for aircooled SOHC flat sixes ain't so big you know. Oh, ok, double that number again because of twice the number of lobes per cam cuz we got 4 valve engines and SOHC 911 is 2 valve. Still, I might be willing to pay as an alternative to some funky regrinds. I hate ******* regrinds.

 

[shojuan]

srfdude:
I just did a quick AutoCad sim/drawing of a couple different SHO cam profiles. They clearly show the total width of the shim is used, although no doubt the pressure/load is greatest as you get toward the center. I can send a small GIF if anyone wants to see what they look like.
Mike

Send it to Scott.

 

[shojuan]

sdpatt:
The design of the SHO's or any other direct acting mechanical bucket (DAMB) valve train could not be allowed to apply a significantly non-centered force to the tappet. A force out of line with the direction of motion of the valve stem and tappet would result in rapid wear within the tappet bore and possibly excessive friction and jamming of the tappet. That would not be an acceptable design for a high velocity valve train mechanism.

Scott, think of a gentle scraping on the side of the shim before the cam lobe rotates to the center applying full force downwards right in the center of that sucker. If you drag your heels on the ground you won't break a bone but you'll chafe the skin. Yeah, different hardness. You grind your teeth together you'll wear them down but you won't chip a tooth. If you drag sandpaper across an aluminum can over and over again you will wear the can without denting the metal. Sand with some pressure and that can will dent. Drag the sandpaper across the surface and only that surface is going to wear.

 

[shojuan]

sdpatt:
That's what I can see with my eyes. Slide a thin feeler gauge under the gap and see how far it goes. I'll bet with an infinitely thin gauge the gap goes all the way to the wear area in the middle of the shim. Also, since the tappet rotates, any "wear" patterns other than perfectly circular on the shim could not be caused by the motion of the cam lobe.

bs Same mechanism of wear as in rod bearings. There's a 360 degree gap between bearing and rod that has a clearance that most definately doesn't require your infinitely thin gauge. That clearance is filled with oil. There is wear over time. More so if you drive that bitch hard.

<small>[ June 12, 2003, 12:21 AM: Message edited by: shojuan ]</small>

 

[Mike Kopstain]

Lol, thank you for this topic.

People listen when you say it. When I said it, the response was something like "You question Scott? No soup for you!".

Just ribbing ya Scott.