If I remember right, 70 lbs is pretty close to the seat force
recommended for a stock cam. Most racing cams use more. I recommend
95 lbs for my cams, but you will see others recommend much more. The
more I look at this stuff the more I believe this is due to some of
these cams not having or not using a ramp. The ramp is a low rate of
lift (velocity) area where the lash is taken up and the impact occurs.
I recently looked at a cam (not for a Triumph) from a big name
manufacturer. With the recommended valve lash, the impact velocity was
about half the maximum velocity and more than 5 times what it should
have been. This is like hitting the valve with a hammer to open it and
slamming it down on the seat when you close it. Under these
circumstances the valve will bounce unless you have strong spring
force. I have never looked at the G3 cam, so can't say anything about
it, but I have observed this problem on other racing cams (Triumph and
non-Triumph) and I believe it is the reason for such large spring forces
even for our little engines with light valve trains.
see http://www.tildentechnologies.com/Cams/Tip_Lash.html
On 5/8/2012 4:50 PM, Tim Murphy wrote:
The cam is a Kastner G3 and the rockers are stock TR4 with 1.55:1 ratio.
The measured cam lift is 0.342 giving a measured valve lift of 0.480 with
0.016 tappet clearance. This gives an actual ratio of 1.45:1, valve lift +
tappet clearance to cam lift. We use a "red line" of 6000 RPM.
I checked Good Parts but he only lists TR6 parts, at least that I saw. Are
the TR6 and TR4 valve springs, retainers, keepers and spring seats
interchangeable?
Thanks,
Tim and Ryan
1961 TR4 #317
From: hotmail_b17abf0a244adefd@live.com
[mailto:hotmail_b17abf0a244adefd@live.com] On Behalf Of Kas Kastner
Sent: Tuesday, May 08, 2012 3:54 PM
To: timmurph@fastbytes.com
Subject: RE: [Fot] TR4 Valve spring - pressure, assembled height, suppliers
i cannot help you with a parts without a lot of photos which I might not
recognize anyway, BUT, that is way way to low a seat pressrue. I don' know
your cam, but if it is high lifter from Larry or something like my old G-3
then you want about 125 pounds on the seat.
Never be beaten by equipment
From: timmurph@fastbytes.com
To: fot@autox.team.net
Date: Tue, 8 May 2012 13:40:23 -0500
CC: ryan.murphy@fdlco.wi.gov
Subject: [Fot] TR4 Valve spring - pressure, assembled height, suppliers
The machinist doing the work on our cylinder head tells me that we only
have
about 70 pounds of pressure on the seats. He thinks this is pretty low, in
his experience with other engines. He also asked if I had the assembled
height of the springs, i.e. how much compression when assembled to the
head.
He usually has this spec and shims the spring to obtain the specified
height. Lastly, the alloy retainers are pretty beat up and the origin of
the springs are unknown and he thinks they look questionable. Who are the
suppliers of valve springs, retainers, keepers and spring seat hardened
washers for racing purposes?
Thanks,
Tim and Ryan
1961 TR4 #317
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