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Old May 01, 2010, 07:53 AM
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Four Stroke Valve Grind

Now that I have replaced the ring in my OS 48SF I need to clean up the top end. I have worked on old Harleys(1948) for years and we always lapped the valves at the start of the riding season if they were not to far gone. Would I do the same for the 48FS four stroke? When are the valves to worn and has anyone did a grind job on these little engines? I'm almost afrad to ask about the valve guides, they look to be cast into the head in a single bronze unit that has the valve seat and ports in one unit.
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Old May 01, 2010, 08:09 AM
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Unless they leak, don't touch anything. Lapping the valve to the seat is common, but it's easy to go too far. Once the guides are worn you're stuck with getting a new head. Luckily this doesn't happen often. I do have an Enya 46-4C head with worn seats and guides. I'm contemplating boring out the old guides and installing new. The valves are canted so it's not a simple setup on the lathe and I've been putting it off hoping to find a spare head or cheap parts engine.

I suppose valves could be ground, but this requires a lathe and tool post grinder. I have some I might try to rescue. Valve wear is usually minimal. I've seen some engines with seats that were worn and others that had worn valves. I guess hardness is not controlled tightly.

Greg
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Old May 01, 2010, 08:40 AM
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Interesting thought on lapping the valves. Usually the valve guides get loose after a while so lapping wouldn't help any there. I think most of the time people replace the heads if the valve seats or valve guides are out of spec. I probably would not mess with it, but if the engine has a lot of time on it, it wouldn't hurt to give it a nice and easy small lap job.
One has to be careful as some engines had only aluminum for the valve seat, maybe they hardened it some, hard to say, aluminum looks like aluminum no matter what the alloy is. Other engines had bronze inserts for valve seats. So it isn't a hardened steel valve seat like you see on larger engines. So when lapping the valves back in one has to be careful as one can quickly go too far. Which might force you to have to grind a little off the valve stem to get the valve clearance to work. Then if they had some special hardening there, you could quickly lap or grind through that thin layer.
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Old May 01, 2010, 10:39 AM
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After cleaning the ports and valves, I inspect the seats with my jewlers loupe or geezer goggles (magnifying visor) checking for imbedded/compacted carbon, etc. in the seat areas...I will usually do a light lapping of the valves just to make sure the seat areas are clean.

I use a kitchen cleanser like Comet or Dutch cleanser mixed w/ light oil (like 3-in-1) into a yogurt like consistency...very little is required...just a few drops of mixture.
I use a pin vise to grab ahold of the tip of the valve stem, and just pull gently while spinning between my fingers.

The process only takes a minute or so per valve...
On the O.S. 's with the bronze seat/guide inserts, there is virtually no danger of harming anything.
On Saito's w/o any inserts, just the Chrome on aluminum, you just have to be gentle...but the amount of time spent is minimal and you're not removing anything but varnish/soft carbon gunk, so to damage something as hard as the chrome on the seat in the head, you'd really have to work at it.

Clean-up is with cotton swabs and lacquer thinner or carb cleaner.
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Old May 01, 2010, 11:08 AM
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Another method. If there is a clear band around the seat and valve, don't touch it, as mentioned above. On the other hand, if there is a shiny or clear metal on one side of the valve and black on the other it needs to be ground as it is slightly warped, the seat/head can warp too. You can replace the valve but it would be a good idea to seat it in anyway. I use either toothpaste or Bon Ami. Grinding compound is way to course. I twist the spring side with slight finger pressure on the inner side. When you get a clear line around the valve and seat, your good to go, doesn't matter about the width if the line. Doesn't matter if it's wide on one side and narrow on the other, as long as there's a clear line all the way around. Scrub the seat and valve with rubbing alcohol and a rag a couple of times. Any particals left on will continue grinding the valve. reassemble and give'r he##. This is my method. there are many others.
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Old May 01, 2010, 05:47 PM
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Hey Gord...last night I dreamed I was a muffler...
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Old May 01, 2010, 05:53 PM
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Did you wake up totally wiped out too.

Gord.
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Old May 01, 2010, 06:08 PM
Airplane Gearhead
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Yep...exhausted...
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Old May 01, 2010, 06:35 PM
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LOL great stuff. Heard that from Betty White on Golden Girls. She'd be the one to say that.

Gord
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Old May 03, 2010, 03:26 PM
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It would seem to me that grinding the valves is over doing it. The valve seats are bronze and valves are steel. I would think after a good flight of say 8 minutes, the valves would have pounded any leaks out of the bronze. Yes, I realize that the faces will be come work hardened, but then so to the valves. Not worth the risk of ruining a head.

Cheers,

Chip
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Old May 03, 2010, 06:10 PM
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I lapped the valves on an old Saito 65 that I have. I used Bon-Ami cleanser and oil....as was mentioned above. I however subscribe to the "use power tools whenever possible" school of thought. I put the bon-ami goo on the valve, inserted the valve into the guide, and chucked the stem in the cordless drill. I then gave it a few revolutions until there was a clean band on the valve and seat. That engine has been running great for four years now. Really....I only did the lap job because I bought the engine apart on ebay for really cheap. It didn't have the valves, so I bought new ones & figured I'd better do something to match them up to the seats.

Dan
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Old May 03, 2010, 06:33 PM
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Done many valve jobs for guys in the club with no problems afterwards. Before I retired, I did valve jobs on marine engine diesel heads two feet across with valves with heads 8 in. across and stems 2 ft long. Refaced on a lathe then ground in by hand. Poured varsol in the porthole and if the seat leaked you did it all over again. Also the place I worked for was licensed to do aircraft heads. Gord.

Gord.
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Old May 04, 2010, 09:11 AM
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Wear seems to vary engine to engine. I rebuilt a friend's magnum last year and the seats where fine while the valves were worn significantly. An OS I had had worn seats, while another OS had worn valves. I have an Enya with worn seats and guides while the valves are fine.

Greg
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Old May 04, 2010, 10:35 AM
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While not specific to the OS question I was surprised to learn that many valve seats do not have the same "classic" profile we are use to with full size poppet valved engines. Attached is what I saw when I looked at some Saito "big bore" engines.
http://www.rcgroups.com/forums/showp...7&postcount=20

All the best,
Konrad
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Old May 04, 2010, 10:54 AM
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That is most fascinating. I wonder if the raised ring portion of the valve seat wears down over time or not. I can see that raised ring as being useful to get the valves to bed in faster and maintain a seal OK.

if my old SAITO 80 stops running good, I will pull the head off and take a look. But since it still runs great I haven't had any interest in taking it apart.
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