Onan 16HP engine

[ras101]

So guys, I bought a 1979 446 with Onan B43M from a neighbor last year. I runs ok, but not well, and has a major oil leak, dropping oil onto the deck when running so in less than 1/2 hour the level drops from full to empty, or close. Not had time to strip it down yet and will not till spring. The neighbor had it serviced every year since new too. What/where should I concentrate my efforts?

[DavidBarkey]

So guys, I bought a 1979 446 with Onan B43M from a neighbor last year. I runs ok, but not well, and has a major oil leak, dropping oil onto the deck when running so in less than 1/2 hour the level drops from full to empty, or close. Not had time to strip it down yet and will not till spring. The neighbor had it serviced every year since new too. What/where should I concentrate my efforts?

If you fill to the full line . Does it leak when not running , ie. just sitting ?

[ras101]

Yes, it seems to but more when running. I am thinking it could be the oil pan gasket but it's too cold to check right now.

[DavidBarkey]

Yes, it seems to but more when running. I am thinking it could be the oil pan gasket but it's too cold to check right now.

Pan gasket is above the full line a little bit . The dip stick tube seal, oil drain tube , additional oil drain plug (some have for other spot) , Cracked/ broken foot , are all possibilities . It would not hurt just to get a rebuild gasket set and change all gaskets and seal as most will be around 50 years old anyways . That is what I did with the genny enginein the 446 even though it was low hours .

[ras101]

Dave, I think you could be right on here. My neighbor is not short of money (he is a Doctor) and had the GT serviced every year since new by a professional shop. It will start (reluctantly) and run, and sounds great, it's just the oil problem. It came with a deck that he used year round and cut great, but nothing My neighbor tells me he gave away a snowblower (never used) a few years ago that he bought with it as a package.

[ssmewing]

Targeting the oil leak is not the route needed. You most likely have gaskets that are all rock-hard from age and heat. The heat that destroys the gaskets comes from running lean. The carb needs cleaning, the 2 piece manifold is probably leaking.

I have my tips and videos on my pages on Facebook and YouTube as Hemlock Case Guy. I have had great feedback on them.

Onan does not sell a gasket kit. Aftermarket junk from China is often sold as a kit. They are not worth the box they ship in.

Boomer sells new gaskets and is good at getting you the correct gaskets. Onan parts are only sold through authorized dealers and they are all sold at the same prices unless it is eBay. EBay sellers have to pay about 15% to sell on eBay. That usually gets rolled into the price.

Boomer's number is 651-437-2826. He can email you the service manual for torque specs and instructions. John Deere wrote an extended version of the service manual called Onan CTM2 service manual, google search for that. It has way more pictures and more precise instructions.

Overall you should correctly clean your carb and use a service kit from Onan. You should search for my help in testing the intake manifold and testing your valves. Both are most likely just a formality and they both should fail the leak tests. You will need to get the carbon off the face of the intake valve. Then you lap the valves to read the lap and see that it passes the test for contact. You also going to be looking right at the camshaft when you do the cover gasket and the shaft seal. The cam bearings have about half the life of the main bearings. You can look at them and see the uneven colors and such. It adds a lot of complexity and stuff like having or buying or making drivers for crank seals, cam bearings, and valve tool to remove the valves. Then the really going for it is taking out the crankshaft and such and having the bore honed at a machine shop. Their hones maintain a perfect circle. If you end up at 0.005 or under for the bore you can use the Hastings rings which have way better oil control from the start compared to the Onan parts.

I do this to all my Onan engines. I do not add oil to any of them. Once the oil gets to the add mark, I am well past the 50 hours. So, I use that as a time to change the oil metric. I run one season with regular oil and synthetic after that.

But, there is a good part. If you do all this correctly, you will never have to do it again.

[ras101]

So, I guess guys you have convinced me to just strip it down and a do a full rebuild. I know that I should have just done that anyway but I guess I was hoping for the "quick fix" . So come spring I will take the engine out and strip it down.. In the mean time it just sits in my yard covered till spring.

[ras101]

I managed to get to the engine this weekend and found the oil leakage problem almost immediately - the oil drain! This GT had been serviced by the same 'professional" shop and I guess over the years they had managed to loosen the pipe into the block. when I went to tighten I found the right angle fitting was hitting the hydraulic pipe to the oil cooler. other than draining the hydraulics and removing the pipe are there any other solutions?

[Eugen]

I managed to get to the engine this weekend and found the oil leakage problem almost immediately - the oil drain! This GT had been serviced by the same 'professional" shop and I guess over the years they had managed to loosen the pipe into the block. when I went to tighten I found the right angle fitting was hitting the hydraulic pipe to the oil cooler. other than draining the hydraulics and removing the pipe are there any other solutions?

Hard to picture what's going on. Can you show a photo of that area

[Timj]

I looked at my 448

It's pretty close, I don't know if you can pry the line up enough to get the elbow off or not. Mine moved some with my fingers but...
Tim