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Discussion Starter #1
Hope there are some Onan experts that read this. Have an 89 318 with Onan 18 hp at 951 hours. Oil dripping from the front of the engine. While changing the front gasket and seal noticed Welsh plug fell out in my hand and discovered the front camshaft bearing looks awful with pieces of it missing. Front crankshaft bearing looks great. Can the camshaft be removed without removing the valves? Would save a lot of cost of gaskets and time if I could just replace the cam bearings and welsh plug along with some other gaskets.
 

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Sorry, the valves need to come out to remove the cam.

It would probably be best anyway, as you'll need to thoroughly clean the engine internally to remove the metal particles from the failed bearing.
 

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rp
as ken stated, tear it down.
most likely you will find more problems.
if the plug fell out , there can be many other problems.
most of these will be related to the camshaft and brgs.
thank you. boomer (the used onan engine parts guy)
 

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Discussion Starter #4
Thanks for your replies and insight. After giving it some thought, I rotated the engine until each valve opened and used a flat washer between the valve and block to hold them open. The camshaft came out easily by tapping it a couple of times with a mallet. Normal procedure would be to completely tear down, hot tank it all, blow out the oil passages and totally rebuild. When I first noticed oil use increasing early this season, I checked compression and found it to be 110 psi on both cylinders. The sparks plugs were clean and normal color, so engine wear was not the problem. Like most mowers, dirt and debris can cover oil leaks, but I found oil building up beneath the front PTO. Assuming gasket wear was the issue, I continued to use it for mowing while monitoring the oil and keeping it topped off until the front gasket and seal came in. After replacing them, the oil leak continued. I took it apart and added gasket sealer, but the oil leak continued and increased. It was not until I put it back together a third time, but left the PTO off and watched as the engine ran that I noticed the welsh plug spinning around. I then realized the oil was travelling around the PTO area and down from the welsh plug and the gasket and seal were OK.

If there is any useful information in my comments for other owners, it is to inspect the welsh plug frequently and suspect it immediately when oil leaks appear on the front of the engine. I had searched the internet for information about oil leaks on the front of 318s and P218G engines and no one ever mentioned the welsh plug. I'll replace the necessary parts, pull the oil pan and totally clean it out. The camshaft bearings are worn, partly disintegrated, but on the outer portion. Hopefully, no metal made it into the crankcase.
 

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rp
WHAT will you do about the bad cam brgs?
i will assume that you have a P series engine.
when the DISH type plug comes out,
that means that the front of the block (in the cam thrust washer area)
is so badly worn that the cam moves to the rear and pushes out the plug.
i have seen this three times on site, in my shop.
two blocks were junk, one was saved by using TWO thrust washers
i think that this is due to dirty oil and the lack of oil changes.
thank you. boomer (the used onan engine parts guy)
 

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Discussion Starter #6
Thanks for the replies, boomer. I definitely will replace the bearings, welsh plug, various associated gaskets and the thrust washer. The camshaft journals are OK and will be polished. I'll check the camshaft travel and other dimensions. I failed to mention in earlier post that not only is the compression quite good, but the crankshaft bearings are in excellent shape. Only the camshaft bearings are worn. Although I'm concerned whether the block will hold a new welsh plug securely.

I've had this 318 for 4 years and maintained it regularly, but I think it had a rough life before and likely not maintained regularly. The paint was brand new and it looked great, but the engine had 2 different spark plugs, different wires for each cylinder and a host of other non-professional mechanical "fixes". I suspect that in a season or 2, I'll need to replace with some other engine. Just attempting to fix this problem and get it through the winter. Mowing season is over, but it's time for firewood and I use it with a trailer to cut and haul firewood for personal use on my small acreage.
 
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