Onan: not the split intake manifold

[nylyon-(Admin) 7,430]

1995 416-8, was running like crap, would hardly stay running, surging the whole bit.  Thinking it was the carb, I took the carb apart, cleaned everything, put it back together, better but still running poorly.  So take it apart again, clean check float level put it back together and the same.

 

 Thinking I am having the split manifold issue, busted out the carb cleaner (luckily already had some for the carb cleaning) and sprayed around the intake.  All was good, except when I came to the front, near the intake port, definite change when I hit it there.  So getting ready to remove the intake, I broke loose the exhaust bolts (no issue what so ever) then broke loose the intake,  Well, well wouldn’t ya know, get to the one intake bolt and it’s backed out like 1½ turns! Thinking the intake gasket has to be trash, I tighten it up and give it a test.  Vrooommmm… Starts perfectly and runs like a champ!  Going to add that check to the 416-H, although that one runs perfectly anyway.

[lynnmor 7,537]

2 hours ago, nylyon said:

 

 Thinking I am having the split manifold issue, busted out the carb cleaner (luckily already had some for the carb cleaning) and sprayed around the intake.  All was good, except when I came to the front, near the intake port, definite change when I hit it there.  So getting ready to remove the intake, I broke loose the exhaust bolts (no issue what so ever) then broke loose the intake,  Well, well wouldn’t ya know, get to the one intake bolt and it’s backed out like 1½ turns! Thinking the intake gasket has to be trash, I tighten it up and give it a test.  Vrooommmm… Starts perfectly and runs like a champ!  Going to add that check to the 416-H, although that one runs perfectly anyway.

 

If you have cheap imported intake gaskets, they can soften and cause the loose bolts.  Always use genuine Onan gaskets there.  Be careful tightening the bolts as they can strip easily and always use a torque wrench.  I run a bottoming tap in the holes and use the longest possible bolts, cut to fit if necessary.

[squonk 42,256]

I guess that's better than having all of the PTO side bearing retainer bolts loosen up and dump all the oil onto your drive way. It happened to me and I got lucky I caught it in time. Onans. You can have them. 

[nylyon-(Admin) 7,430]

Gotta say, I like the Onan’s, tons of torque and they sound amazing

[squonk 42,256]

Yes tons of torque and sound amazing. But stuff loosens up. Intakes, carb mounting bolts, bearing retainers, valve seats and oil filter adapters. Kinda like a Harley! 

[nylyon-(Admin) 7,430]

Well, can’t really argue with that, I just fixed the loose oil drain tube on the hydro, and the 8-speed has the same issue.

[lynnmor 7,537]

1 hour ago, squonk said:

Yes tons of torque and sound amazing. But stuff loosens up. Intakes, carb mounting bolts, bearing retainers, valve seats and oil filter adapters. Kinda like a Harley! 

Amazing, I've had little trouble with that on 4 hard working tractors.  I did have a valve seat loosen on a spare engine that was abused and fins were full of mud-dauber mud.

[squonk 42,256]

I got lucky. I was warming up my 520 in the driveway. I had the snow blower and cab on.I decided to let it run and was straightening out the garage. The spot in the garage where it had been parked was clean. I got done with what I was doing and when I returned to the tractor there was oil everywhere. If it had happened when I was actually moving snow I probably would have blown it up. I had to put about a qt. and a half back in

Edited Thursday at 12:28 AM by squonk

[Bill D 2,079]

I have 3 Onan P216's now.  I think I like them better than my Kohler's.  Smooth, powerful, great sound under load.  Sure they have their quirks, but then so do I! Once you know their issues and how to fix/modify them to solve their problems, they are great engines.

 

 I won't touch a P220.  Too many issues with valve seats.  Not worth it for four extra horsepower.

Edited Thursday at 06:19 PM by Bill D

[kpinnc 13,428]

10 hours ago, Bill D said:

I won't touch a P220. 

 

I think that nails my issues with Onan engines. 

 

Quite honestly a P216 or P218 does indeed have fewer problems, even without the valve seat concerns. 

 

That being said I have a P220 in a Toro Groundsmaster that had well over 3000 hours on it when the deck rotted out. But it also had a remote oil cooler. I'm certain it would crank even now after sitting for a couple years. 

[lynnmor 7,537]

9 hours ago, kpinnc said:

 

I think that nails my issues with Onan engines. 

 

Quite honestly a P216 or P218 does indeed have fewer problems, even without the valve seat concerns. 

 

That being said I have a P220 in a Toro Groundsmaster that had well over 3000 hours on it when the deck rotted out. But it also had a remote oil cooler. I'm certain it would crank even now after sitting for a couple years. 

So that extra .030" higher lift on the intake cam lobe is the cause of all the problems?

[kpinnc 13,428]

3 hours ago, lynnmor said:

So that extra .030" higher lift on the intake cam lobe is the cause of all the problems?

 

I have no idea. I believe the amount of heat on a P220 is also at issue. 

[cleat 6,911]

I have the exact opposite experience. 

I have never had a valve seat issue in a P220 but I bought a basket case 416 a few years ago with a P216 that had the block so beat up at the valve seat (front one) that it could not be salvaged.

[Bill D 2,079]

8 hours ago, kpinnc said:

 

I have no idea. I believe the amount of heat on a P220 is also at issue. 

I think it's heat plus the larger bore.  This makes the area between the cylinder wall and the valve seat just thin enough to cause problems.

[onanparts.com 184]

On 3/28/2025 at 5:40 PM, Bill D said:

I think it's heat plus the larger bore.  This makes the area between the cylinder wall and the valve seat just thin enough to cause problems.

Nope. ^^^^^^

 

P216, P218 & P220 Blocks are identical inside and out. All with 3 1/4" STD bores.

 

Example:

500 blocks at the beginning of the assembly line. At the end? 250 P216's, 125 P218's and 125 P220's. Internal parts determine what model. P218 and P220 are identical twins if not for the higher lift cam and larger carb jets on the P220.

 

Several production runs where the seats were not peened or peened correctly to lock in the seat happened at some point in time. Of the millions made, a small fraction had this issue. Debris clogging the head etc. can and has caused those seats to come loose.

 

If you want to be happy for a day, Drink! Want to be happy for a year, Marry! Want to be happy for a lifetime? Take care of your Onan!

 

 

[Bill D 2,079]

56 minutes ago, onanparts.com said:

Nope. ^^^^^^

 

P216, P218 & P220 Blocks are identical inside and out. All with 3 1/4" STD bores.

 

Example:

500 blocks at the beginning of the assembly line. At the end? 250 P216's, 125 P218's and 125 P220's. Internal parts determine what model. P218 and P220 are identical twins if not for the higher lift cam and larger carb jets on the P220.

 

Several production runs where the seats were not peened or peened correctly to lock in the seat happened at some point in time. Of the millions made, a small fraction had this issue. Debris clogging the head etc. can and has caused those seats to come loose.

 

If you want to be happy for a day, Drink! Want to be happy for a year, Marry! Want to be happy for a lifetime? Take care of your Onan!

 

 

Thanks for the clarification.  I always thought the 220 had a larger bore.  

[onanparts.com 184]

7 minutes ago, Bill D said:

Thanks for the clarification.  I always thought the 220 had a larger bore.  

You betcha! It's the Big Block, big brother to the small blocks that has a larger bore. P224, 24HP.

 

 

[lynnmor 7,537]

Did you ever notice that the Onan Service Manual is way off in regards to the press fit of the intake valve seat?  The specs in there show a nominal .0305" press and that ain't gonna happen.  The exhaust shows a nominal .0030" press which is a more reasonable figure.  I shoot for a .0055" press on the intake seat and I would bet that Onan didn't use an adequate press in addition to the peening issue.