tapping on top of engine. valves??

Hi all,

i have a 1968 sears super 12. model number 917.25311. It has a 12hp. tecumseh model number 143.582132 in it. There seems to be a tapping sound coming from the front top part of the engine. Im almost positive its the intake valve, but not 100%. Could it be something else?? I took the valve cover off on the front of the engine to check the valve gap between the stem and lifter. Tecumseh manual says intake should be .010 and exhaust should be .020. The exhaust gap is fine, but the intake gap is at .019. Sounds like that may be the problem?? If it is the problem how would i go about adjusting the gap, bringing it closer??

Thanks for your help
Alan

You need a valve job. the engine needs to be partialy disassembled and the valves ground. The shop grinding the valves will set the proper gap. This is not expensive.

what is involved in a valve job?? Could i grind the valves? I was hoping to do the work myself and learn, so i can do it in the future too. Even if i have to buy some specific tools, that would be ok.

There is no mechanical adjuster on the valve system on the L-head engines. If a valve is too tight, you grind a SMALL amount off the end a little bit at a time until the clearance is right. If it is too loose, you either get a new valve (hard to find and expensive) or lower the valve in the head. That is accomplished by removing some of the surface area of the valve or cutting the seat.

You'll have to evaluate the engine to see what course you want to take. What is the overall condition of the engine? What do the valve and seat look like? Is the valve cracked or burned? Does the valve have an obvious concave area in the center of the seating area? (I bet it does...most do) Are the valve seats tight in the head? What is the compression? Have you done a leak-down test? Is there a possibility that there is some junk jammed between the valve and seat that is keeping it from closing?

Assuming that everything is OK and you just want to get the clearance right again, you have three options. All involve some amount of engine disassembly requiring a valve spring compressor for valve removal.

1. Quickest and easiest: Lap the valve. This involves using some type of device to spin the valve in the seat after putting an abrasive paste in between the two. Doing this will further exacerbate the concave area of the valve where it contacts the seat. Also, extreme care must be taken to remove all lapping material from the engine prior to reassembly. This is probably the least desirable option regarding engine longevity.

2. Harder: Take the valve to a engine machine shop to have it re-ground. You will still want to lap the valve lightly after this if you don't do any work on the valve seat.

3. Most difficult: Replace or regrind the seat and re-grind or replace the valve. This is best done on both valves at the same time following a complete tear down of the engine. At this point you are inspecting all mechanical parts to ensure they are in spec. Keep in mind too that if you fix just one part of an ailing engine, the other ailment will be magnified once it's back together again.

thanks for your help spence, i am going to go with option 2 and see how it goes!