First timer: Opinions on my lapping job please

[dtlx11]

Hi Cruiersforums
Long time lurker here, been following google searches to this site for a long time and its been an invaluable source of experience and knowledge, but now I humbly ask for a little personal help.

My Carter has a Yanmar 3GM30 in the Engine compartment and this winter I'm attempting an overhaul. I'm making a video of the whole process so that others can watch it and hopefully do the same. Among many other things I took the head off and lapped the valves. I just recently did a quick test I read about which was to pour a suitable liquid into the intake port and check for leaks. It did leak, but only very slightly. Can someone watch the video and tell me if the seal is sufficient?

Youtube

Thanks in advance for any help

[Old Snipe]

Depends on what "gear head" you ask. I never liked doing a leak test after lapping unless it was on a re-machined head assembly with new parts.

Questions:

New or old guides? Any stem wobble in the guides?

New or old springs?

Were the springs tested?

A decent valve lap can fail a leak test but still give hundreds of hours of service.

Used guides have their own wear patterns that will affect seating angles during static testing.

Weak/older springs can affect a leak test. Always do a spring compression check. You can do it with simple tools.

I used to do a lot of grinding and lapping. On older engines that I was reusing the old parts and just trying to squeeze a little more life out of, I always checked the stem to guide, and if they were still fairly tight.... I would lap away. If they had wobble......new guides at least.

A valves position to the seat (static) is not what the position will be when the with the engine running. This goes double when you are reusing the old parts. The assembly will find it's own operational seating angle after it's been running for a while and seat accordingly.

Take a close look at the any valve assembly after a tear down and you will see how each assembly has a very slight wear angle compared to the other valves.

I prefer bluing the valves when reusing older parts because the seating angle between the seat and valve is the best you can hope for in a static condition anyways.

[GordMay]

Greetings and welcome aboard the CF, dtlx11.

[dtlx11]

Thanks for your reply Old Snipe:

Guides are the old ones, I'm having trouble sourcing new ones for a decent price + delivery (I'm in Belgium and there seems to be some form of cartel on Yanmar parts). There was little to no wobble, in fact there was quite a lot of resistance when pushing the top of the valve stem through the guide.

Old springs, I'll have a research online about how to test them unless you know of a good source directly?

I wasn't aware of the bluing technique, I'll have a look into that. What bluing material/dye do you recommend?

I was a little disappointed with the leak, I spent quite a lot of time on each valve. Like you have done in the past, I'm trying to squeeze some more life out of old parts so replacing each part feels a bit of a waste of cash when I know 3 or 4 seasons down the line I may end up putting a new engine in.

[Old Snipe]

I have a small bottle of DYKEM blue pattern/layout dye that has lasted me for years. Some welding suppliers stock it, or you can google it to find a supplier. I think it is about 6-7 bucks. Just brush it on and let it sit a minute, then lightly wipe off the excess. There are other brands that work just as well or better.

I don't use the suction cup hand tool for lapping either. I prefer to use a low speed reversible drill with a hose and clamps. Put a light coat of oil on the stems. Dab on some compound and work the drill in both directions 3-4 seconds with a very light pull of the valve against the seat. When you have gone both directions .....stop and check the bluing. Repeat until the bluing haze turns to a light haze.

You are working with used parts, so most likely you will still have tiny pits on the used seats. Don't try to remove them or you will risk removing too much material. All you are trying to do is freshen up, and help Concentricity a little.

I will PM you a simple and effective method for checking valve spring compression/height.

[Ex-Calif]

I wouldn't be happy with that drip but I tend to be anal about such thigs.

Why take it apart if you aren't going to make it perfect...

[dtlx11]

Pitting on the valve seats is definitely the problem. The valves themselves shined up very well but I could see the seats were not the same quality. I don't think any more lapping will help the problem as you say, it will remove too much material.

I think I will just check the springs and re-assemble the engine as planned (new gaskets, injector overhaul, new fuel tank and low pressure lines, paint touch up) and see how it runs. A professionally refurbished engine, and a newer model to boot, goes for around 2-3k. If i were to replace all the parts I was unhappy with it would run to more than that. But of course I would rather spend the money on new sails, and the mooring fees are due. Ho hum.

[a64pilot]

Heads off, get the valves done professionally, this is a Diesel and due to the higher pressures a good valve seat is more critical, I also believe you might can have the valve guides knurled if they are worn and replacements can't be had, but I've never done that, I've always replaced them.
Be very careful with a drill if you go that way, it's easy to cut too much.
I didn't look at your video as low bandwidth, but gold standard is alcohol and no leak, maybe wetting after a while, but no discernible leak

[dtlx11]

Just in case anybody stumbles across this thread in the future:

I had another go with the lapping compound(s) and supplied tool as well as a flatblade screwdriver. I also used a Dremel with a soft wire brush attachment to really get the first layer of dirt off both the seat and the valve head. I really pressed down with the screwdriver and coarse grade compound to grind away the mating surfaces then smoothed away with the fine grade after. Upon re-assembly not a drop could be seen seeping through so I'm going to move onto the next phase of the re-build.

Thanks for any help

[Ex-Calif]

Good work! Glad you went the extra maile and you will be too...