OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Gxv 120: oil in valve housing?

I use a propane torch - heat the carbon until it turns grey/white, then it wire brushes off. If you don't have a torch (or access to an oxy set), oven cleaner and a lot of elbow grease will do it. Soaking in water overnight will soften the stuff, too.
One of the tricks my brother & I used to use in the (bad) old days, was to spray water into the carby (whilst the engine was running), let the engine recover, then do it again. Repeat a few times, then go for a drive around the block. The difference it made to old side-valve four cylinder cars was amazing. (showing my age a bit, there!!)

I haven't found an efficient way to remove hard oxide from valves. What I do, is use a rotary wire brush, but stay away from the part of the stem that slides in the guide. The wire brush removes the carbon and other chippable materials, leaving something that is valve-shaped, but may have black areas. I ignore those, and get on with the lapping. (Of course the seating surface, on both valve and seat, must be completely free of black after lapping.) Incidentally I apply the wire brush quite firmly - valves are not delicate when you are using a tool softer than they are - but do not touch them with a grinding wheel.

As soon as you begin lapping, you will see whether you are getting full-circle contact on both valve and seat. Once you have a full circle, you are lapping to make it wide enough. If it is wider in some places than others, the correct procedure is to re-cut the seat and/or have the valves ground in a proper valve grinding machine (depending on whether it is valve or seat that has the varying contact width). Permissible seat width for both inlet and exhaust is 0.8 to 2.0 mm. About 1-1.2 mm sounds excellent, so long as it is continuous all the way around - do not tolerate any radial lines or cloudy patches.

From what you have said, it appears that the stems and guides are in very good shape and you can proceed to lapping. Remember when you are lapping be very, very careful that no grinding paste gets into the valve guide, or you will ruin it immediately. Just keep the paste onto the seating area, by checking it and cleaning it off frequently. Use a separate cloth for wiping the grinding paste - do not allow it to touch any other part of the machine, and throw it away as soon as you finish the lapping job.

Well, the machine is back together and sounds great! no more smokey engine, no more bad compression on start, now starts 1st time every time again.

I have found a good mixture for removing excess carbon from valves.. commercial grade oven cleaner! works a treat! turns the carbon to slime when i left the valves to soak in it.

As to the valve lapping, the IN valve was easy, started with fine compound and looked good with about 2 dozen turns, the EX valve (in particular, the seat) was a bit more of a pain, there seemed to be some kind of scratch on the seat and i had to use the coarse grain and then revert to the fine grain compound but it all worked out well!

I also went and bought myself one of those small spring type hones, for 20 dollars i was happy! ill try post the photos of the honed cylinder now, only thing is, i was scared to keep honing because the bore was past the service limit already, so there are still 1-2 spots where i saw the honing tool did not kick in.

the only problem with the mower now is that the blades on the base plate seem to be loose even though they are assembled correctly and tightened fully, does this mean its time for a new base plate (this is usually the case with victa so im just guessing), can i do anything about this? it just makes a clunking sound on stopping as the blade hits the plate thats all.

also, i ran the engine on idle for a couple of minutes then decided to switch it off, repeated this a few times before trying the high speed, is there anything else i should be doing for break in of new rings?

photos of the hone are up in the photo section of the forum

Try to avoid loading the engine up (running into long, thick grass really fast)for the first hour or so of operation.
After the first cold/hot/cold cycle, check for oil leaks and check head studs, blade bolts, etc.
After a rebuild, I usually do an oil change after no more than 1 hour of operation, and after that, as per the owners manual.
Enjoy!

Recommended process for honing is to run the hone slowly and pull it in and out of the cylinder rapidly so the marks in the bore are helical, not circumferencial. However what you have done has broken the glaze - the problem is that the rings may catch on those narrow circumferencial grooves. If it seems OK after the first time you use it, and it doesn't use oil, chances are there is no problem. Other than that it sounds like a good outcome - that should be a really good mower engine.

doh! i kinda thought as well that the scores were too circumferencial but the instructions at the back of the hone said run at approx 2000rpm! i had the hone going at 1200rpm and i was vigorous with my 'pumping' :P, i guess i need to slow it down even more next time?ight switch the drill to screwdriving mode as this is roughly 400rpm)

also, any tips with those loose blades grumpy?

Personally, I wouldn't be throwing away a blade plate unless when you remove the blades, you can see that the metal around the holes has been worn down rather substantially. I suggest you clean it up so you can see what condition it is in, and if it is OK, look at the parts to see why the nut will not screw down the thread slightly further. If the blade plate is OK and you have run out of thread, my solution would be to fit a washer of suitable thickness to the opposite side of the blade plate to the side the blade goes on. If you need to do that, though, be careful to fit identical washers to each blade, or you will put the rotating system out of balance, which is a bad idea.

again, thanks grumpy for all the invaluable advice!

Glad it all worked out so well, Johno. By the way, I forgot to answer your question about honing speed. If you watch it being done on new engines on a production line, it looks like probably less than 400 rpm, with plenty of kerosene being pumped over it to carry away the grindings, and the hone moving up and down full stroke about once per second. The forward and reverse cross-hatches are at something like 30 degrees to the axis. The reason to remove the ground-off material so vigorously is so that it won't get run over by the next honing stone, which would make scratches. It needs to be kept wet with low-viscosity oil-based material, and if you can't flood it, you need to stop frequently and wash both bore and hone. (This is very similar to filing when you want a good finish.)

I'll close this thread.