# Does anyone know how to fix a bad exhaust valve?



## thehandyman1957 (Feb 11, 2017)

Well hello folks. About 8 months ago I got my hands on a Generac 66LP Propane Generator. It was running fine but had a few hick-ups (popping and lagging). It has a GN-480 two cylinder engine and when it starts the lagging and popping it bogs down and pretty much dies. I have replaced the carb regulator and have a new tank with new regulator on it. It produces power fine when it's running good and after going in and adjusting the valves (.003) and the plugs (.030) and noticing that there was no gap on the valves I have come to the conclusion that perhaps I have a bad exhaust valve or perhaps even both. I did some digging and I cannot find any parts for this otherwise awesome generator. Does anybody know of a way to repair valves or a place that might sell a valve kit? Monsoon season is only a few weeks away and I thought I had everything ready and then this. It's going to be a huge job to disassemble this unit just to get the heads off. 

I know some of you have been around for some time and have many years in generator repair, so any advise is welcome.

I have attached a pic of the repair parts list for this generator.


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## motormonkey (Jul 10, 2016)

> It produces power fine when it's running good and after going in and adjusting the valves (.003) and the plugs (.030) and noticing that there was no gap on the valves I have come to the conclusion that perhaps I have a bad exhaust valve or perhaps even both.


I could interpret that sentence as saying that it's running good now after adjusting the valves. If so, problem solved, no harm done.

I could also interpret that sentence as saying that it's still not running good after adjusting the valves. The problem could be valves, but it could also be something else.

If the valves are leaking, the engine would likely fail a basic compression test with a compression gauge. You can also look for other clues that the valves are leaking. Pull the shroud off the engine so you can get to the flywheel and/or the flywheel nut. WITH THE PLUG WIRES DISCONNECTED, turn the engine over by hand or wrench to the compression stroke on each cylinder, feel for compression, and listen for air leaking out through the intake or exhaust.


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## thehandyman1957 (Feb 11, 2017)

Yes, your second interpretation is correct. I adjusted the valves and it still does it. I will try your advise in the next day or two
Thank you for the tip. I'll get back when I find out.


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## Handyhiker (Sep 29, 2016)

I am sure you looked in the book for the specs but I have never seen a valve adjustment that tight, .003 To me any heat and you will wind up with no valve lash. Just something to try might be to go to .010 on the valves and see if it makes a difference. I can't recall right now but I think my Champion sets are around .010 intake and .012 exhaust cold.
One other thought, it could be carbon built up around the valve and seat. I have had good luck using Barrymans B12 Chemtool to decarbon small engines. You can run it straight or mix with a little fuel, load the generator with a light load just to make it work a little. This has saved me from tear downs several times and is a cheap test.


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## thehandyman1957 (Feb 11, 2017)

Thanks guys for all the great advise. Handyhiker, I normally would have been worried about that also. My manual does not have the valve adjustments in it and I had to do some digging and only found one site that mentioned it. So I did a bit more digging and found a manual for a GN-410 and it's valve clearances were pretty close 0.002-0.004 in. So before adjusting I could not hear any clatter at all as they were super tight. After adjustment they clattered. Making me think they were too far out. 

So first I took motormonkey's advise, and checked for any hissing noise and the left cylinder was hissing like crazy. So I went ahead and pulled the head. This is what I found (see pics). It looks like it's blowing by the head gasket on the exhaust side. You can see the discoloration on the bottom of head. I cleaned up the valves and they look great. Held up to sunlight and there is no bleed at all. 

I'm not entirely sure the head isn't warped. I have not had any luck finding parts for this gen set. At the very least, I need a set of head gaskets.

While I was waiting to upload these pics I found some head gaskets on Ebay for 20 bucks a set. Will order today.

All that was left of the head gasket was a metal insert. I'm sure the other isn't too far away. So I will replace them both.


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## thehandyman1957 (Feb 11, 2017)

Well, I ordered the gaskets. I pulled the other head off this afternoon after the weather cooled down a bit and you could tell it was doing most of the work. Much heavier carbon deposits on the piston and you could tell the head gasket on that one was leaking also. So I cleaned everything else and the valves look good. All the other gaskets are in great shape and this should go back together pretty easy. I found the head torque values finally so all should be good. Fingers crossed. I will update when I get it put back together.


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## motormonkey (Jul 10, 2016)

Since you have the heads off, confirm that your valves aren't leaking. Turn the head so that the intake and exhaust ports are up, pour some liquid into them, and look on the combustion chamber side to see how much is leaking out past the valve. A little leakage can be expected, a lot means you should pull the valves and make them right. Kerosene, diesel or even water works good for this.


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## thehandyman1957 (Feb 11, 2017)

That's a good word, I will do that. Thank you : )

Update: Well I did a test on both heads. Using Rubbing Alcohol with plugs in I got zero on the second head, intake or exhaust, super tight. The first head, (the one I pulled off first) Zero on the intake but a small amount of weeping on the exhaust. Enough for the rubbing alcohol to wet the stem. So I took out my Tom's Toothpaste and lapped the valve with my drill on low for about 10 seconds. Washed it down and tested again. I did this twice. Now it weeps only enough to see it slightly damp on the very underside edge of the valve seat but does not go any further before evaporating. So I'm gonna say that's pretty good. Poor man's valve job. Toothpaste is a light weight abrasive and does great if you just need a little bit of smoothing down and you happen to live out in the middle of nowhere like I do with no valve lapping compound hanging around.

Update: Well I decided to take it off just to see as I could see some rings in the seat and sure enough it's got these indented rings all the way around the seat and just a little bit in the valve. I don't think I could lap this if I tried even with some good lapping compound. If I put rubbing alcohol on the valve and blow compressed air from the bottom I get air bubbles. At this point I'm not sure what else to do as I cannot get any replacement valves for this gen set. Too old (20+ years). I'm not sure If there is a place that could grind the seat back smooth and smooth out the valve. I'm probably going to have to live with it the way it is and hopefully at least get my money back out of it in use this year. I will see if I can't find a machine shop around here and give them a call.


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## RonJ (Aug 5, 2015)

Have you tried Generator Guru - I see they list Generac in various Models? I have followed your post and the various inputs....it is interesting to follow. Ron


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## thehandyman1957 (Feb 11, 2017)

Yes, I even called them. But they are super high. They wanted $120.00 just for the two head gaskets and four valve cover washers. I found the same exact ones (by chance) just as I was talking to them on Ebay for only $19.00 for the pair. I can't imagine what they would want for the exhaust valve if they even had it. I simply can't afford it. The big problem with this unit is it's age. There is simply nothing out there anymore. The only reason I even found the head gaskets on Ebay was because I simply put the search (Generac Gasket) and looked to see if I could find one that matched. They didn't have the model or part # on them, which is why I could not find them when I first started looking. I tried that with the valve but no go. 

I put a call into a guy in Lake Havasu AZ (about 70 miles away) and I'm waiting for a call back. Trying to see if they could grind the valve and seat for me while I wait so I don't have to make two trips.


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## Handyhiker (Sep 29, 2016)

Good luck with your search. Keep us posted. I understand the no parts available thing. Some of my older sets take some serious looking to find parts.


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## thehandyman1957 (Feb 11, 2017)

Well, no luck finding someone to grind the valve so it will just have to do. The head gaskets are on their way and no matter what, it will be 100% better than it was. If it will run long enough to get us through monsoon season then it will have been worth it. I had no idea how old this generator was when I purchased it. Lesson learned. I might try lapping it just a bit more and see if I can get it to seal better.


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## motormonkey (Jul 10, 2016)

In desperation, I have clamped a drill in the vise, chucked a valve into it, and went at it with a file and stone. It wasn't pretty, but it worked.


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## RonJ (Aug 5, 2015)

Thinking outside the box - works when all else seems to fail. Ron


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## thehandyman1957 (Feb 11, 2017)

Thanks Motormonkey. I took your idea and ran with it, and I think even improved the idea. My biggest worry was that I would not be able to keep the angle right or even keep it round. So I came up with another idea. I had some 220 grit velcro sand paper for my multi tool, so I cut it so that it would rest on the valve (see pic). I then used oil and my drill to re grind the seat and valve. I then did the same thing with 650 grit and then with 880 emery cloth for both the valve and the seat, simply by turning the sand paper upside down. Doing it this way helped me to keep the right angle and the difference was huge, though you might not be able to see the ridges in the first "valve before grind pic", it was so bad you could feel it with your fingernail. Same with the valve but not quite to the degree of the seat. It now does not bleed any rubbing alcohol at all. It does bleed a bit of air if I use a compressed air nozzle behind it, but not as much as before. I believe that the seat is just a bit out of round causing it to allow some air bubbles on the top of the valve in that test. So the first pic is of the valve seat before the first grind. Then the tool I created on the valve. I did the same set up for all three types of grit. The 5th pic is the seat after the first pass. The last pics are of the final product. Again, this was a huge success for me, as I simply was going to have to leave it due to the inability to get it done professionally. I think it will work very well. Tell me what you think?

Update: I decided to check the other valves on the other head to see if they had any air bleed, and they do the same thing. If I use water I get very little air bubbles, but if I use rubbing alcohol (thinner) I get more. I suppose the springs could be a bit weak and thus contributing to this air bleed. But I think this is the best it's going to get. I did an extra run with the emery cloth on both the valve and the seat just for safe measure.


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## RonJ (Aug 5, 2015)

I know I said Generator Guru, but meant to add eReplacementParts. I seen it, they also have an extensive listing Brands they cover. This has been a great Post to follow - I read and learn from these type inputs and the inputs from everyone. Ron


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## thehandyman1957 (Feb 11, 2017)

Well, I checked at eReplacementparts and it was nada. Good try though. I'm excited to get this thing back together and see how much better it runs now that it won't have two blown head gaskets and bad exhaust valve. I'll update when I get it running. : )


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## Handyhiker (Sep 29, 2016)

Very nice sir. My hat is off to you. We can't always make the oldies perfect but we can make them better. NICE JOB!!


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## thehandyman1957 (Feb 11, 2017)

Thank you Handyhiker, I'm quite surprised how well it turned out. I will be keeping this fix in my bag of tricks.


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## thehandyman1957 (Feb 11, 2017)

Well, after a long 4th of July wait, I finally got my head gaskets today and they are a perfect fit. Took a gamble as there weren't any part #'s to go by. It's still pretty hot here but I hope I can get it put back together this coming Monday morning.

Our first thunderstorm is supposed to be here Sunday 
so it will cool down a bit making it tolerable in my metal sweat box, er I mean shed. : )


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## thehandyman1957 (Feb 11, 2017)

:tango_face_grin:SUCCESS!!!! The thing purrs like a kitten : ) Ran everything in the house including the central AC and was still getting 110 off of both legs and 220 across both hots. No popping or spitting.

Now it's an oil change and filter and to see if I can find some valve cover bolt gaskets. 

Thank you all for your support and helpful hints.:tango_face_wink:


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## thehandyman1957 (Feb 11, 2017)

Well, I ended up having to use flat rubber washers and metal washers to replace the valve cover bolt gaskets as you can't get them anywhere that I can find. Changed the oil and filter (oil was really dark) and she's ready to keep us cool when the power goes out. 

We just missed a heavy storm system last Sunday night, rolled just north of us going east. Was a nice lightning show though. : )


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## RonJ (Aug 5, 2015)

Congrats....you have worked hard on this one - now it will work hard for you! Ron


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## thehandyman1957 (Feb 11, 2017)

*Blown Away!*

Hello folks, well you all know the story of my rebuild generator and how that turned out. Well as that was moving along we decided to sell our place. So we sold a bunch of junk to get it out of the way and moved into a smaller mobile while the paper work gets done. After we had completely moved out the only thing left was the generator in the shed and the 50 gallons of propane. I had it listed on Craigslist for almost a month with no one, not anybody showing any interest for the whole kabang. Generator, Tank with 50 gallons of propane, New battery and cables, 5 quarts of synthetic oil and a small solar panel and controller for the battery. I was asking $500 for everything. 

So I took the propane to the new place and reset the price for $ 300, still nothing for over a week.

So that brings us to yesterday. Out of the blue a guy calls me and says he wants it. He gets to my place around noon. We do all the usual stuff and he pays me the money and I go back home. It's about 12:45pm.

At 1:00pm we get a huge storm in the valley with up to 80mph winds and it just ravages the whole area including my place.

So I come back to see the damage, and the shed that the generator was sitting in mounted to a wall three hours ago was completely ripped apart. Took the roof right off and parts of it were scattered over 100 feet away.

This storm showed up literately 15 minutes after I went to my new place 8 miles away.

Then, even more mind blowing was that my 5th wheel and all the awnings and tarps were still in perfect shape. I only lost one grommet out of all of them. Meanwhile the RV Park next to me lost all but one awning.

The shed was no big loss. I hated the thing anyway, and it now gave me the excuse to tear it down. I got almost 3/4 of it torn down this morning.

The funny thing about this was, I purchased and fixed the generator for just this kind of stuff. Power was out for over 4 hours and it was super hot and muggy. But if we had still been there we would not have been able to use it anyway and it would have been just dowsed with the torrents of rain that came with that storm. And mind you, this shed isn't made with cheap metal. Each of the sections weigh around 40lbs and are heavy gauge steel.

So I attached some pics of all the area including my shed and my place. It's like the last scene in Twister where one house was completely untouched and the whole area was mowed down. Awesome!:tango_face_surprise


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