[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.
>>
>>
>>
>>     Unsubscribe/Manage:
>>     http://autox.team.net/mailman/options/healeys/michaelsalter@gmail.com
>>
>
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