[Healeys] Valve clearances

[Kees Oudesluijs]

When the engine heats up the clearances get smaller, so stick to the 
recommended clearances at least for the exhaust valves. The inlet valves 
can be set to the min value or very slightly less to allow as much 
mixture in, but set the exhaust valves to at least the min. value to 
prevent burning of the valves. To large a clearance will cause damage to 
the valve train: tappets, followers, valve stems and, worse, the camshaft.

Kees Oudesluijs


Op 13-1-2019 om 16:55 schreef 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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