I'm in the process of rebuilding my old boat's Ford 302 engine, marine spec, 1996 block but with none roller hydraulic tappets, 1993 heads. The boat was new to me in June this year but I soon found out the engine had a knock, misfired in certain conditions and was down on power. When I ran a compression test river water spurted out of cylinders 1 through 4. I pulled the engine, stripped it and found some badly scored pistons and cylinders. I managed to hone the cylinders and fit new pistons myself. Bought new marine exhaust manifolds (found a crack in the marine manifold that was on cylinders 1>4) so hopefully when the engine's rebuilt it should run OK.

Now I'm looking at the heads. I originally intended on just looking at the valves on the couple of cylinders that read low compression, hoped to find nothing wrong with the heads (put the low compression down to the condition of the old pistons, bores and rings), then I decided to give all the valves a bit of a re-lap, might as well while the heads are off. Most valves lapped in OK with minimal lapping but I had to spend a lot longer lapping 4 of the valves in to get rid of what could be described as a very light burned area, or at least it took a lot longer to get that lapped in look on those 4. Instead of a straight 45 degree edge / mating area most of the valves mating areas have a slight curve to them, one of my questions is how much curve is OK? I'm not too bothered about it making every possible hp but I do want it to run OK and not have to pull the engine again soon after refitting it. I bought 4 new valves to replace those with the most curved mating faces but I don't know whether to refit the old valves which are lapped to the seats or fit the new valves and obviously have to re-lap them again. Seems that if the valve mating area is curved but they're lapped in OK the valve seat must also be curved, so if I start lapping new valves into curved seats I'll end up having to do a lot of lapping... The new valve mating area with the seat will still be curved but not curved as much as it is now.

Picture of an inlet valve with the curve on the mating area, this isn't the worst valve but it was easy to take a picture of this one because it's already removed


slightly curved valve mating area

 

Lapping isn't a valve job. What needs to be done is to grind the valves and then the seats. This will not only a face and seat that are flat and at the correct angle they will also have the right width and placement on the valve faces. Most of the time I grind 2 angles, a top using a 15, 30 or 37 degree angle to narrow up the seat. Then I come in with a 45 and grind the seat itself. This keeps it from getting too wide and too high up on the valve face. Sometimes another angle is ground to narrow it up from the bottom, usually a 60 degree. Then you're good to go again. No big deal really.

 

Lapping compound will not correct an improperly ground or worn seat or valve. New valves should always be ground before use. It's important that all valve tips end up being the same height when a valve job is done.

 

The newest valves may have a hard face and they can't be cut. You may want to confirm that you should cut them.

Like tire balancing, machining, and many other things, if you remove the item you are checking and install it on the machine again, it will not be true. Maybe in the 70-80's you might want to cut a new valve, I would not do anything with today's parts. A good lapping would confirm if you are good or not.

I don't buy cheap Chinese junk so if you are buying new $5 valves, maybe you need to recheck them.

 

Our main grinder is an old Sioux that's been modified to use a collet chuck. This gives it a lot of range for valve stem sizes and it makes it very repeatable. Most of the time if a used valve is good it will take less than .001 to touch off all the way around. If you take it out and put it back in it is less than that and generally a few tenths.

 

Thanks all.

I bought all new valves from Rock Auto and had a local machine shop recut valve seats and fit new bronze guides.

The heads are good now and I've just fitted them.

This boat engine has none roller hydraulic lifters. I was concerned that if I just refitted lifters (while pumped up) it could cause valves to stay open and/or piston to valve contact. So I removed the clip from top of lifters and dismantled them to drain the internal oil.I realise I could still have the opposite problem, lifters might not prime or stay pumped up so could 'bottom out', I could have tested if they'd pump up by compressing them while in a bucket of engine oil but I didn't do that. The plan is to prime the oil system by turning the oil pump before running the engine anyway, but will doing so prime them and pump them up?

I have a few questions about firing order and distributor stabbing..
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It's a 1996 302 with 2 barrel carb in a boat, there's a sticker on the marine exhaust manifold that reads firing order is 13726548 but I don't know if that would have been correct originally and I don't know for sure if its the original engine that is still fitted (though it is still a 1996 none roller hydraulic cam engine). I've also read firing order could be 15426378. Wish I'd made notes or marked up plug leads and noted the distributor position before I removed the engine but I didn't! I could probably work out ways to find firing order, careful watching of rockers etc, but can anyone suggest an easy way of finding firing order?

The marine distributor is electronic (no points), it doesn't have vacuum advance. Where would the usual position be for number 1 cylinder (distributor orientation)? Am I right to assume that after I've stabbed the distributor the rotor arm should point to almost the centre of cylinder 1's electrical contact inside the distributor cap when cylinder 1 is at TDC on its compression stroke? Is there a way to electronically test what would be the position when points would open with the (assumed original) Ford OMC Cobra electronic marine ignition? If it had points I'd expect to be able to fairly accurately set timing using a multimeter to find when points open and make sure the rotor arm was close to the centre of #1 distributor contact when #1 cylinder was at TDC but I don't know if that's possible with the OMC Cobra electronic ignition..?

Thanks again.

Simon

 

I think that you'll just have to line up the rotor to the #1 position in the cap. Put the cap on the distributor and then put a mark on the distributor body in line with that lug. Then when you install the distributor make sure that the rotor is pointing at your mark. That should get it close enough to start, run and set the timing.

If it is a '96 engine the firing order could be either one. Are the plug wires still hanging on the cap? If not, I think that I would start with the 154 order and see what happens. You won't hurt anything.