[Healeys] Valve clearances
Kees Oudesluijs
coudesluijs at chello.nl
Mon Jan 14 00:47:10 MST 2019
On cast iron engine the difference may be very little, but if your
engine has an aluminium head the difference may be noticeable.
Kees Oudesluijs.
Op 14-1-2019 om 00:51 schreef Bob Spidell:
>
> I've set valve lash cold, then checked them warm and not seen an
> appreciable difference.
>
> On another note, I'm a convert on the "set the gap per the cam
> builder's specs." Next job for the BJ8: set valve lash to 0.015" per
> DWR spec.
>
> Bob
>
> On 1/13/2019 3:23 PM, Michael Salter wrote:
>> This is another subject that I often wonder about.
>> If the valve clearance is there to ensure that the valves are fully
>> closed when the engine is hot then why, when I check the clearances
>> on a hot engine after a dyno run, are they hardly any less than they
>> were cold?
>> I can appreciate that the valve train components grow because of the
>> heat but surely the block and head and rocker shaft pedistals also
>> grow and thus there is little if any net change.
>> I also appreciate that the exhaust valve stem get really hot but ????
>> Just wondering....
>>
>> M
>>
>> On Sun, Jan 13, 2019, 6:42 AM WILLIAM B LAWRENCE <ynotink at msn.com
>> <mailto:ynotink at msn.com> wrote:
>>
>> I disagree that valve clearances are not critical. As the engine
>> comes up to temperature the metal parts of the valve train
>> (valves, lifters, push rods, the head itself and the rocker shaft
>> towers) increase in length and the valve clearances are
>> calculated to assure that this expansion isn't allowed to affect
>> the sealing of the valves on their seats. If the valves are set
>> too tight they reach a point where they won't touch the seats and
>> therefore won't seal. Hot gases rushing through the gaps will
>> quickly erode the valves. Also increasing the duration and/or
>> lift of the cam has the effect of the decreasing the length of
>> the opening and closing ramps on the back side of the cam This
>> reduces the length of time (dwell) the valve remains on the seat.
>> Increasing the valve clearance restores the dwell time the valve
>> needs to transfer its heat load to the cooling system through the
>> valve seat and the cylinder head. Too little dwell time or the
>> lack of proper valve sealing are two causes of burned valves.
>>
>> In my own experience I installed an Isky cam with a grind a
>> little more aggressive than the 100M cam and set the clearances
>> to 0.012" per the manual. Within about 2,000 miles the exhaust
>> valves were trashed. I then took the time to read the Isky
>> installation instructions which specifically state the valve
>> clearance needs to be set to 0.018". I re-installed the head with
>> new valves and set them to Isky's spec and never had another
>> problem with burned valves.
>>
>> Follow the cam grinder's recommendations and you will avoid trouble.
>>
>> Bill Lawrence
>> BN1 #554
>> ------------------------------------------------------------------------
>> *From:* Healeys <healeys-bounces at autox.team.net
>> <mailto:healeys-bounces at autox.team.net>> on behalf of Bob Spidell
>> <bspidell at comcast.net <mailto:bspidell at comcast.net>>
>> *Sent:* Saturday, January 12, 2019 11:10 PM
>> *To:* Michael MacLean; healeys at autox.team.net
>> <mailto:healeys at autox.team.net>
>> *Subject:* Re: [Healeys] Valve clearances
>>
>> I should note the rockers are pretty noisy at 0.015; IIRC I
>> tightened them up just a bit.
>>
>>
>>
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>>
>
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