[Healeys] Valve clearances

[David P]

Absolutely correct......


On 1/12/2019 11:26 PM, WILLIAM B LAWRENCE 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> on behalf of Bob 
> Spidell <bspidell at comcast.net>
> *Sent:* Saturday, January 12, 2019 11:10 PM
> *To:* Michael MacLean; 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.
>
> On 1/12/2019 2:39 PM, Michael MacLean wrote:
>> I'd go with .016.  You can always tighten it.  Better loose than tight.
>> Mike MacLean
>>
>> On Saturday, January 12, 2019, 11:01:32 AM PST, Bob Spidell 
>> <bspidell at comcast.net> <mailto:bspidell at comcast.net> wrote:
>>
>>
>> Makes sense (for some reason).  I put a DWR1 cam in my BJ8 which, 
>> according to DWR, 'is a little better than the BJ8 cam and so works 
>> well in any standard or mildly tuned car' but I think the 0.015" 
>> applies to all profiles on the spec sheet.
>>
>> Bob
>>
>> On 1/11/2019 8:48 PM, John Rowe wrote:
>>
>> Simon,
>>
>> Modified cams require the large clearance (don’t ask me why?) So go 
>> for .015 that is what mine is.
>>
>> John Rowe
>>
>> Qld
>>
>> Australia
>>
>> *From:*Healeys [mailto:healeys-bounces at autox.team.net] *On Behalf Of 
>> *simon.lachlan at alexarevel.plus.com 
>> <mailto:simon.lachlan at alexarevel.plus.com>
>> *Sent:* Saturday, 12 January 2019 9:14 AM
>> *To:* Healeys
>> *Subject:* [Healeys] Valve clearances
>>
>> The car is a MkII BT7.
>>
>> The BMC manual says adjust the clearances, cold, to 0.012”.
>>
>> Denis Welch said I should go 0.015”, cold, after fitting their “Fast 
>> Road” cam.
>>
>> The rolling road guy said 0.016”, warm.
>>
>> I have the radiator out right now so I can get a nice socket onto 
>> that nut and have a go at the clearances.
>>
>> Stick with 0.015”, cold?
>>
>> Thanks,
>>
>> Simon
>>
>>
>>
>> 	
>>
>
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