Do very cold temps affect valve adjustments?

Assuming a linear expansion rate, the difference between 40 degrees and 65 degrees is pretty minimal compared to the difference between 65 degrees and 200+ degrees.

I typically try to set clearances to the "tight" end of the spec anyway but not less than minimum.

 

forgive my ignorance. I always thought valves tended to get tighter with time not looser?

 

Some people like to go toward the tight end of the adjustment range to pick up additional lift, though I don't know how much one gains from the practice. I shoot for the middle of the range.

As far as wear, there is a system of components here with competing wear rates. In my experience, the valve to valve seat wear dominates and the clearances tighten with miles/hours on the engine. The one exception is a Benelli Tornado triple I own which had soft shims in a shim under bucket architecture - the valve would beat a divit into the shim and open the clearance a bit.

When I measured the shims on my 456 recently, I noted some wear in the shims but all of the shim to cam clearances were tight with the exhausts all under spec indicating that this wear rate was siginificantly less than that of the valve to valve seat.

 

In an overhead cam motor with direct valve actuation - If the valves and seats are stable, wear on the cam and/or shim and/or follower cause a loose condition. If there is a problem with the valve (tuliping or stretching) or seat (collapsing or sucking) then they will get tighter.

Rick

 

Bo, you're probably best off to run the engine up to full operating temp, and then let it cool for a good 45 minutes in your (coolish) garage while you're getting ready to do the gap measuring. She'll be in the warm range, neither stone cold nor at full operating temp. Warm is easy on the hands.....

 

Bo,
Interesting qustion. I expect the true effect is quite complicated to work out as both head, valve seat, valve, cam follower, shim and cam expend with temperature and in 3 dimensions and at different rates. I am not sure it is true to say that everything moves in the same direction. If the head and valve seat contract more than the valve head, it may have the effect of pulling the valve down which will increase the valve stem top to cam heal clearance. However, in simple terms, consider a 100mm long steel valve stem expanding on warming from 40deg F to 70deg F, the extension is ~0.9thou(inch). The workshop manual tolerance (ie. max to min acceptable) on valve shim to cam heal for the 246Dino is about 2thou for both inlet and exhaust. I would have thought staying in the middle of the tolerances should be OK. If you have a spare valve measure it with a vernier and then warm it up and check it again. Shoud give you an idea of the maximum change in clearance.

I am posting this as just replaced a starter ring gear on a flywheel. I calculated the heat needed to get the ring hot enough to slip over the top of the flywheel rim. The calculations and measurments work out quite nicely. I don't claim to have used the exact thermal expansion coefficients for the steel alloys but it is useful to get an idea of the values involved.

Kevin
http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html
steel temp range 32 to 400 deg F 0.00000730 inch/inch F
thermal expansion dL=LoAdT
deg C deg F
tmin 4.4 40
tmax 21.1 70
mm inch
valve length at Tmin 100.0 3.937
valve length at Tmax 100.0 3.938
expension/contraction 0.0122 0.0009

 

It's tricky to make assumptions when you have multiple parts made of different materials all expanding and contracting together.

I would stay within the specs, I doubt you will notice a difference.

It would however be helpful to compare clearances when warmer.

 

Ferrari has an acceptable range of 2 thousandths. There will be ZERO difference to the way the motor will run within that range. Your feeler gauges come in 1 thousandth increments. The difference in adjusted valve lash on a cold day compared to a hot day will not be detectable with that feeler gauge set.


Forget the weather and just adjust the valves. Spend your time worrying about something that CAN actually make a difference.

 

I am further north than you and was wondering the same thing while doing a major on my 348 engine last February in my rather cold garage. I ran the salamander for a few hours pointing it directly at the lump (which was out of the car) to take the chill out of the core.

One other interesting thing that I discovered concerning valve lash during that major was that clearance will be very subtly effected if one turns the crank actuating the valve just momentarily then back. There seems to be just a bit more drag on the feeler immediately after valve actuation??