valve timing

[Will N]

I was reading through the recommended way to set up the valve timing, and I'm baffled by the need to set the valves using the position of the pistons. I surmise that the procedure was used to compensate for varying valve stem lengths and wear on the cam lobes. But wouldn't the same thing be accomplished by just quoting what the required clearance is between the tappet and valve stem?

 

[Will N]

I searched the board and found this response that Redmodelt gave:

Depends on if you are using adjustable or solid lifters. Is your cam new, reground or used?
Used cam and solid lifters= piston travel method
Used cam and adjustable lifters= piston travel method
New or reground cam and adjustable lifters= .010 intake and .012 exhaust. I have seen references of using up to .016 for both the intake and exhaust.
The lobs on the original cams were not indexed too well and there were small differences in the the location of the holes for the wrist pins (piston and rod) and crank journals. That is why you use the travel method with the older parts, to get the valves to all open at the same point on all the cylinders.

I guess I understand that the variation in the crank journals and cam indexing could cause performance issues that you can compensate for by the recommended procedure. But doesn't there have to be some minimum and maxium tappet to valve clearances too in order to avoid burned and noisy valves?

 

[yachtsmanbill]

Hey Will... this very subject has always amazed me. Any decent mechanic should be able to feel and visualize when the CAM is at bottom center and then set the valves. The rocket scientists make a big deal out of setting lash between .010 and .025 as tho youre gonna get an extra 1000 RPM out of a blown roller small block chevy. These are 2000 rpm L4 engines that make a whopping 5 horses per slug.
I set mine at .015, they are quiet and I get 50 mph outa the speedster. Period. I wish I had a nickle for every solid lifter Ive set off the timing mark on the front dampener on a SBC while all the pro's were struggling with a degree wheel. Sometimes I just wanna say ARGHHH! ws

"Ran when last shut down" eh? How would Fritz the farmer do it in the barn in 1933 by oil lamp??

 

[Doug Money]

I believe the reason for the timing method is the cams wear at an uneven rate. In this 5HP per slug motor, smoothness gets you more power but more noise. If the lobes wear uneven, then the clearance method will get you some cylinders with more power than others and less noise.

 

[Will N]

The way I figure, if one cam lobe is worn more than the others, there’s no way you can finagle the valve clearances to have that cylindar work just like the others. The nose of the cam probably wears faster than the heel, causing less lift on that valve. So even if you set the clearances so that it opened or closed at the same relative piston position as the other cylinders' valves, the reduction in lift is going to cause that cylinder to have less power than the others.

If the reason for the piston travel method is because of variation in cam indexing and piston pin location from cylinder to cylinder because of machining tolerances back in the day, if you try to compensate to get the valves to open in the same relative piston position, you’re going to end up with some valves with more clearance than others. The tight valves might burn (particularly if they are exhaust valves) and the loose clearance ones will be noisy. Seems like I’d rather have an engine that runs a little rough because the valve timing is a tad off between the cylinders than having valves burn or be noisy.

And Bill, what is that crap in your valve chamber on the first picture- mice nests?

 

[yachtsmanbill]

When I dragged her home I was gonna try a start after freeing it up, but after seeing the grooved low speed drum I decided on an overhaul... that turned into the engine, mag, trans and rear end and everything else in between. By far, 'twas the ruffest flivver Ive done to date! ws

Amongst other issues was the missing oil filler cap... that was the death blow!!