16 hp Onan welsh plug leaking

[Pettybilt 3]

Hey guys, i have a 416-8 with the Onan with 520 hrs on the clock, she runs like a top. However i did notice that the welsh plug behind the pto is leaking, and maybe loose. I under stand that the camshaft is on the other side of this plug. I was reading about a guy who had to replace his Onan, he stated the reason for replacment was something about the camshaft walking and a welsh plug. That was what the dealer told him anyway. Well that makes me nervous.

Can the plug be replaced, or is this a lost cause?

Thanks, Doug

[56hotrod 0]

Hey all, my name is Tom and this is my first post. I have been reading a ton of posts here the last few weeks and saw this one by pettybilt and I have the exact same issue on my 1993 416-8. I would really like to know if anyone else has dealt with this problem or knows the proper way to fix it. I ordered a new welsh plug and I am waiting for it to arrive to swap it out and hopefully it will fix the leak. I noticed when I was running my engine the plug looked like it was sort of vibrating like the cam was touching it. This engine has 649 hrs and runs like a top. Any help is appreciated.

[Pettybilt 3]

I noticed when I was running my engine the plug looked like it was sort of vibrating like the cam was touching it.

Mine vibrates like you are talking about, first i thought it was the valves ticking. With no responses, i figured it was unique to my tractor.

Maybe the onan experts will chime in, HINT HINT.

Come on someone here to of seen this before.

Thanks, Doug

:)

[Kelly 1,033]

My 20hp was leaking but I was in a rush so I cleaned it with carb cleaner, and a small wire brush, and put silicone on it, no leak for now, I know it was a bandaid not a fix, but it is working so far.

[300zx 7]

I have never had the welsh plug leak, but I do have an engine with 200 hours that has a knocking sound all of the time, cold/hot/idle/increasing rpm/high rpm. It doesn't sound like a rod knock. I have had it apart and found nothing. I had a suggestion by someone on another forum that it might be end play on the cam. I plan to check it when I get a chance. If your welsh plugs are vibrating, I am now wondering if that is the source of my knocking and my welsh plug just hasn't started leaking yet.

[300zx 7]

I also put a not on the Yahoo Onan Engine Club's forum to see if they had any suggestions. I will let you know if I get anything.

[56hotrod 0]

I started a thread on the "mytractorforum" here are the links, responses are few. I really cant believe nobody has dealt with this yet. You cant make me believe that a great running engine is no good because there is no proper fix for this little stupid plug that leaks.

http://www.mytractorforum.com/showthread.php?t=145479

http://www.mytractorforum.com/showthread.php?t=145568

[56hotrod 0]

Oh yeah, I got my new plug in the mail today. I will replace the old one and see how that goes. If it does work I'm thinking of tapping the block and have a screw in plug machined to take care of it.

[300zx 7]

56hotrod, if you do pull the welsh plug, see if there is wear in the cam bearing on that end. I am also curious about the plastic washer that was mentioned in the other forum. I can't believe that Onan would use a plastic washer to take the cam shaft thrust. Here is the link to the thread I started in the Yahoo Onan Engine Club:

http://groups.yahoo.com/group/Onan_Engine_Club/message/6457

What are you going to seal the welsh plug with?

Good Luck!

[56hotrod 0]

if you do pull the welsh plug, see if there is wear in the cam bearing on that end. I am also curious about the plastic washer that was mentioned in the other forum

I pulled the timing cover to check that plastic thrust washer and it is in one piece and looks to be in pretty good shape. I'm pulling the cam out in a day or two and will check the bearing wear. Also the new plug was only $1.50 from onanparts.com.

I'm probably going to use permatex #2 for the sealant. Anybody have a better suggestion?

[Pettybilt 3]

So i take it the welsh plug is a press fit? Does'nt seem like much. I'm thinking if the welsh plug is loose then maybe the hole in the block has opened up, (got bigger). I have used shaft retaining compound from loctite. Not sure if this is the same stuff i used, however seems like it would do the job.

http://www.midwayusa.com/viewProduct/?productNumber=220112

Doug

[Pettybilt 3]

Here is a service manual i found, hav'ent had time to look through it yet.

The link don't work, you'll have to copy and paste in.

home.comcast.net/~lyon.family1/WheelHorse/Onan_Engine.pdf

[300zx 7]

Doug, the welsh plug should be dish shaped. It should just fit the hole, dished out. Then you have to flatten the dished out part to tighten the plug in the hole. I grabbed this quote from another site, trying to find you a how to: "To install [a welsh plug] take a socket about 1/2 the size the plug and pound it in until its fits usually the plug is flat but not concaved in". I hope this makes sense. I have never used the sealant you are planning to use, but it looks like it should work. Good luck and let me know how it goes. Was there any end play on your cam?

[Pettybilt 3]

I havn't checked my cam end play, i've be running pretty hard the last few weeks. Thanks for the info on intalling the plug. I'm hoping to tear it apart this winter, figured i'd put the engine on the bench and look at then. Maybe i should be bump this up the to do list. If its as simple as installing a new plug, does'nt sound like to big a job. 56hotrod, sounds like you have got yours tore apart, look like an easy fix?

Thanks, Doug

[56hotrod 0]

pettybilt, I had to order a valve spring compressor so I can get the valves and lifters out so I can pull the cam out. I would imagine after the cam is out its pretty much just taking a long punch and driving the old plug out. Here is a link to the new plug.

http://onanparts.com/index.php?main_page=p...&products_id=66

[sorekiwi 761]

You can probably punch a hole in the old plug, or screw in a sheetmetal screw to pull the plug out from the outside. The cam is right behind it, so be a little cautious.

But you say the plug is loose, so it probably wont take much. A lot quicker than pulling the engine apart...

[300zx 7]

I agree with sorekiwi, usually you just drill a big enough hole in the plug to wedge them out, unless you have another reason to pull the cam.

The same type plugs are used on car engine blocks. In this case they are called freeze plugs and are designed to push out if water freezes in the block to prevent cracking the block. On a car block, drilling a hole and wedging them out is your only choice.

I am still really curious about what made your plugs loosen up. I don't think they did it on their own. I still suspect the cam is hitting the plug and will continue to do so if we don't fix the cause.

Keep us informed on what you find.

[56hotrod 0]

Well I drilled a hole and pryed the old plug out. Then I sat the new one in the hole, removed the timing cover, grabbed the camshaft gear and pulled it away from the plug and then pushed the cam back up against the thrust washer and it didnt touch the new plug that was just sitting in the hole. I figured if it was touching the old one then it would be because when it was flattened out it was probably flattened too much and was touching the cam and the vibration would have loosened it and cause it to leak. Now another problem that will make me have to remove the cam is when I pryed the old plug out I nicked the cam bearing so I will have to pull the cam anyway and replace the cam bearings.

Here is a picture with the plug removed

Here is a picture of the camshaft pushed all the way against the thrust washer

Here is a pic pushed as far as I could away from the thrust washer

New welch plug

Hopefully someone can figure out why it was leaking. Also on the inside of the old welch plug there was no rub marks at all indicating the cam was touching it. If anyone needs any other photos let me know and I'll snap them for you. Thanks to everyone helping on this.

Tom

[sorekiwi 761]

Interesting pictures.

You could put a DTI (Dial gauge) on the cam and measure the end float. There is a huge tolerance on this in an Onan (.011-.048"). I have a P220 that has .046" and although it is (just) within spec, I was a little worried that this much end float would upset the operation of the govenor (which is on the front of the cam gear on these engines). Later it occured to me that with the helical cut cam gear that on power the cam would be pushed toward the block, and the only time the cam gear (and governor mechanism would come forward is on "over-run" when the throttle is closed anyway.

I would agree that if the cam had pushed the plug loose, then there would be a witness mark on the plug. Since there is none, I think we can dismiss that as a cause.

I have heard of (but not seen) of Onan cam bearings coming loose in the block, probably due to having been overheated, but again I would think there would be a witness mark. The couple of cam bearings I have pulled out of Onan blocks have been loctited in, and they were as tight as a nuns nasty!

As far as the nick you put in the bearing, I guess that is it at the 4 O'clock position? Do you think you could just scrape the high spot off, preferably with a bearing scraper, but a sharp pocket knife would work too. Normally you dont want a gouge in a bearing but remember on the Onan that the rear cam bearing is not pressure fed, it is lubed by splash, so you wont loose oil pressure by a gouge in the bearing there. As long as the high spot around the gouge doesnt cause the cam to bind, I dont think it will cause a problem. Hell it might help you get the amount of endfloat down!!

The only other thought I have is that maybe if the breather got blocked somehow, that enough crankcase pressure might build up to pop the plug loose. But I would have thought it would also blow a lot of oil out through the seals if that was the case.

EDIT: Why dont you ask your question in this thread at MTF:

http://www.mytractorforum.com/showthread.php?t=91204

[56hotrod 0]

I put a dial indicator on the cam after I removed the plug and pushed the cam against the thrust washer and zeroed the dial. Then I pushed the cam as far as I could in the oposite direction until it hit the large plastic washer on the crankshaft and even with the washer deflecting some the max I could make it move was .048. I dont think that is the proper way of measuring this but its all I could think of to do. I also pulled the breather a few days ago and it was spotless and the 4 little plastic balls that I assume act as a pcv valve were not stuck and rattled freely. Here is a better picture of where I nicked the cam bearing and the cam actually will not even touch it because its on the edge.

Here are some pics of how I had the dial indicator set up

This is the dial ind reading with me pushing the cam away from the cam thrust washer and touching the plastic washer on the crank.

[Tgblanken 27]

Wow, I just was looking for the same answer. I Picked up a basket case 416-8. It had a major oil leak. I found the motor full of mice nests and oil soaked dirt. It was so bad the oil filter had a hole in it from rusting. I cleaned it up and got it running. I noticed the cam welch plug was leaking and going in and out. I bet the motor got hot a time or two. I was wondering if your motors puffed smoke when running the rpm up and down due to the welch plug being loose?

Thanks

Terry

[Pettybilt 3]

The only other thought I have is that maybe if the breather got blocked somehow, that enough crankcase pressure might build up to pop the plug loose. But I would have thought it would also blow a lot of oil out through the seals if that was the case.

The crank pressure thing makes me wonder maybe the block expands fast than the welsh plug, and if its not installed properly, maybe the crank pressure could blow it out. I did notice on mine that the welsh plug pulses, its gotta be the crank pressure doing that. It sounds like a the valves are ticking.

Tom, thanks for the pictures.

Doug

[sorekiwi 761]

Thats pretty much how I measure endfloat, I measured at the front with the DTI on the gear.

One thing to note though is that you want the DTI pointing straight at the camshaft, in your pic it looks like it is at a slight angle. This will give you a false reading. Being that you are really close to the tolerance I'd check it again.

The thrust washer on mine was fine, but there is some wear on the face of the block where the washer sits. It bothers me, but I'm still within spec, so I'll let it go.

[sorekiwi 761]

The only other thought I have is that maybe if the breather got blocked somehow, that enough crankcase pressure might build up to pop the plug loose.

[300zx 7]

Great pictures. I am with sorekiwi, I don't think the damage to the cam bearing is bad enough to change. It is still a mystery to me why it loosened up.

Did the cam seem tight in the back bearing? The Onan Club site mentioned lack of oil to the cam bearings can cause them to wear oblong, allowing the cam to move radially front to back.

The crank case pressure does pulsate, that is what makes the fuel pump work. The pulsation may have been what made the plug vibrate while the engine was running.