REFLECTIONS

A Brief Word


| March/April 1999


For seasoned collectors, and those who have been around engines for a long time, much of the following is probably old news. However, there are a lot of folks new to the hobby, and who are oftentimes daunted by the mechanism of an 'old engine.' Figure 1 shows the valves and rocker arm of a typical engine, in this case, it is a Stover.

Valve timing is an important part of getting an engine to run properly, and with wear the exhaust valve wears into the seat, thus getting 'longer' in relation to the rocker arm. Regrinding does the same thing. Usually, the cam design is such that the exhaust valve should just start to open about 10 degrees before outer dead center. This is so that the exhaust valve is pretty well open by the time the piston begins the exhaust stroke. When timed this way, the exhaust valve should close at about top dead center, or perhaps a few degrees past TDC.

When there are no timing marks (and there usually aren't), we just set the valve timing to where it looks about right and go from there. If the valve timing is too late, in other words if it begins to open too late, the engine runs hot, and doesn't sound right. Setting the timing too early, on the other hand, is no good either. The cam dwell is already built into the cam, and that can't be readily changed, so the best way is to begin with a setting of 10 to 15 degrees before outer dead center for the valve to open. It will be pretty obvious when the piston is on inner center what the builders had in mind.

Figure 2 shows the detent setting for a Stover Type K engine. In Figure 2, 'A' is the distance between the latch finger and the catch block with the engine at rest. Notice that for a 2 horsepower engine, this distance is only 5/32 of an inch. Adjusting this gap is important, since it changes the speed differential between being hooked up and dropping out to hit a shot. Oftentimes you will see an engine running at a show, and it slows way down before unlatching, and then has to hit several shots before it hooks up again. In many cases, this is because the gap between the latch finger and the catch block is too large.



Worn parts can create major problems with hit-and-miss governing. If the push rod is badly worn in its guides, it rarely stays in the same place all the time, and as it moves to different positions, the gap referred to above will change. Worn governor linkages can also cause all kinds of problems; there is little other way to remedy these without reaming out the parts and fitting with new pins.

Worn out cam rollers are always a headache. In many instances, we have cured the problem by finding a sealed ball bearing of the same o.d. as the roller, and then fitting up a new pin for the inside race.














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