I had a look around German forums and it seems to be a difference between
tuning and standard engines.
Standard ? flat
Tuning ? domed.
Von: pegandbobm at aol.com <pegandbobm at aol.com>
Gesendet: Montag, 23. Juli 2018 22:17
An: rkrantz77 at comcast.net; fot at autox.team.net; Fubog1 at aol.com;
tr4racing at googlemail.com
Betreff: Re: [Fot] Do(o)med or flat lifters?
Not an expert but I WILL GUARANTEE the lifters in my air cooled German made VW
Formula Vee engine have a slight radius/angle. I check this before each
rebuild to ensure they have not flatten. Pre-Trump I think Germany was still
considered part of Europe>
Bob
-----Original Message-----
Sent: Mon, Jul 23, 2018 1:46 pm
Subject: Re: [Fot] Do(o)med or flat lifters?
The reason for a slight angel on the lifter is to keep it from digging into the
ramp on the cam lobe due to an aggressive acceleration design. Typical
American (cannot say what European mfg. does) lifters have approximately a 60
inch radius. I even have an additional edge radius put on the lifters. The
cam lobes have a slight taper side to side for rotating the lifter. Lift on a
cam is limited by base circle radius which in turn is limited by cam bearing
diameter. Then you get into duration and how fast you can get the valve open.
All the Triumph "flat" tappets I have ever seen have a slight radius. The
rules say you must retain the same type (flat, roller, mushroom) lifter as
stock. My question is "how flat is flat". Rule does not say the lifter has to
rotate. If a lifter has a 0.75 inch radius across the lifter diameter and no
taper on the cam lobe,you can keep the lifter from rotating and accelerate the
cam opening very fast. Think about that.
This may be true for American engines.
All European engines have no angel in the Cam shaft. And all the tappets,
lifters, rollers, are flat. Dead flat. No light with an edge on it.
So maybe this is just an American thing?
Cheers Chris
This is well covered in many engine-building books & I've discussed it at
length with several camshaft engineers over the years.
It's my understanding that the lobe should have a very slight angle ground in,
and the "flat" tappet really isn't, it's very slightly convex.
This will give it rotation, if it doesn't rotate it will wear.
There could also be spring pressure or lubrication issues?
In any case I would discuss it with the tappet supplier before doing anything,
at the least make sure that they are sufficiently hard to begin with and can be
reground.
Glen
-----Original Message-----
Sent: Mon, Jul 23, 2018 6:04 am
Subject: [Fot] Do(o)med or flat lifters?
In the past we had this discussion.
I've bought some high quality lifters from USA, made from tool steel I suppose.
400$ they've cost..... and started to fail. On 3 of them, the very center does
show e few pittings. Also visible that only a small part of the Cam is used..
The cam is okay
The machine shop will grind the lifters dead flat, as they should be, they say.
Cheers
Chris
Yes, lacking access to a Cam Doc, you can use a set of V or bearing blocks, a
degree wheel, dial indicator, and a bit of time, checked at 5 cam degrees,
works fine.
I'm still old school though, I plot them out on graph paper!
That will give you the lobe profile but most folks don't have the full specs on
the cam, usually just advertised lift and duration.
Since the tip of the lobe usually starts to go away first, a simple lift
measurement will reveal the worst, best done with a dial indicator cuz some
(cheap) cams are ground on different base circles.
Generally, ramp wear is unusual if the tip is still OK, although there can be
exceptions.
Glen.
-----Original Message-----
Sent: Tue, Jul 17, 2018 12:38 pm
Subject: RE: [Fot] Cams
By degreeing the cam using increments of 10 crankshaft degrees (5 camshaft
degrees) and then plotting the results in Excel, it is possible to get a very
accurate picture of the profile of the cam.
I?ve attached a spreadsheet showing an intake and exhaust lobe comparison two
years apart of our Kastner G3 cam for reference.
Tim Murphy
#317 TR4
Sent: Monday, July 16, 2018 6:31 AM
Subject: Re: [Fot] Cams
Generally any obvious wear or pitting would make it unserviceable, but the wear
isn't always so obvious.
You can measure the lift and compare to spec, that will show any worn lobes,
but the best way is to find someone who has a "cam doctor". It's a machine that
sets it up and measures the complete profile.
Usually if there is anything apparent that suggests that there may be problems,
there are...
Glen
-----Original Message-----
Sent: Sun, Jul 15, 2018 6:47 pm
Subject: [Fot] Cams
How do I determine if a cam is good or bad. If there are any marks on it does
that make it bad. I do know that two of the lifters has pitting on the surface.
Ronnie
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