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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