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Hi Cam stuff. Mainly for Phil and John.


pete roper
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I was cleaning out the drawer of my bedside table this morning and came across a pair of tappets, (No, I have no real idea why I had tappets in my bedside table drawer, that's just the way it is.) and it makes interesting viewing and probably shows another reason why the 'New' Hi Cam was able to make considerably more grunts than the 'Old' Hi Cam.

Now I have problems putting pics up here but I'll try. If it doesn't work I'll have to rely on the good offices of someone more savvy to copy them from my links.

Anyway if you can see the pics the larger of the two tappets is from an early Hi-Cam, Daytona/Centauro. The smaller one is a flat tappet from a 'New' Hi-Cam, Griso/Stelvio etc. 

http://<a href="https://flic.kr/p/2mv7sh6" title=" by -convertpervert-"><img src="https://live.staticflickr.com/65535/51525265357_428f218e93_z.jpg" width="480" height="640" alt=""></a>

<a href="https://flic.kr/p/2mvfgLC" title=" by -convertpervert-"><img src="https://live.staticflickr.com/65535/51526790904_2e1447f54b_z.jpg" width="480" height="640" alt=""></a>

As you can see the earlier tappet is VAST and in fact weighs 54 grams. The later one weighs in at 22 grams. Yes, it has a small pushrod as well that weighs a few grams but the difference is huge! That is an awful lot more mass to be moving and coupled with the extensive use of low friction rolling element bearings in the later engine contributes greatly I'm sure to the greater output of the later motors.

 

 

 

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Never got the pictures Pete but the statement in itself is insteresting.

Does the "New" Hi Cam rev higher or is the difference simply due to the tappets being lighter and allowing the valve train to work more efficiently due to the reduction of mass and inertia?

I've thought about getting the idler shaft cut so it runs on a single bearing on the front rather than the "false cam" that the early design was, as suggested by Phil and similar to the MGS design. Unless though I'm really at a loose end I doubt I'll follow through with it

Another statement recently that Meinhoff regrading opening the tappet clearance up to hold the exhaust valve on the head longer also intrigued me. Think that was because of long opening ramp on the cam, however I'd have thought that might lead to other problems due to the tappet being suddenly opened and shocked, leading to more wear on the tappet and cam.

John

PS even trying to just use the links I couldn't get the pictures to show, perhaps I'm worse when it comes to being tech savvy. Gotta love this growing old thing

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Usually Docc or someone hauls my tech-less-than-Savvy arse out of the fire on this but pm me your email again, I can't find it, and I'll send them to you direct.

everything in the valvetarin, in fact everything in the motor, saps power. Moving something quickly then stopping it quickly and making it go quickly the other way takes energy. The greater the mass the higher the energy required.

Havent thought about the valve lash issue.

 

sorry, I'm in the middle of cooking supper!:D

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PM sent Pete

Looking like I got all Winter anyway the way the weather's heading

I understand the issues, at least the basics, turning these engines over many times by hand

Just wondered if the mass reduction allowed the newer engine rev higher.

I can't find the thread but I'm pretty sure somewhere you commented on opening up the tappet clearances up somewhere else and didn't approve.

Can't remember if it was Meinhoff or somebody else who suggested it.

I think I can see the pros and cons

For, you leave the valve on the head longer allowing greater heat rejection

Against, the valve is no longer smoothly opened on the cam ramp but has to open start to open suddenly.

John

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I think the size was more dependent on making the rocker arm system work. All that protrudes out of the lifter bore is the very top. Is the cam base circle smaller then on the new engine.

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1 hour ago, Kevin_T said:

I think the size was more dependent on making the rocker arm system work. All that protrudes out of the lifter bore is the very top. Is the cam base circle smaller then on the new engine.

The later 4Valve head system is an improvement on the old style. As Pete has pointed out the lifter is smaller and lighter and has a one piece steel mini pushrod about 35mm long with ball ends that fits inside the lifter and protrudes from the top and engages the rocker arm.

( https://www.stein-dinse.biz/product_info.php?language=en&products_id=12039)  The base circle on a Daytona engine is 21.5 mm and on a roller Griso engine is 29.6mm. A roller base circle can and is usually smaller than a flat tappet so I would assume the flat tappet Griso cam would have a base circle at least as large as the roller cam but packaging will come into it. 

Ciao

 

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