Weight of Onan 20HP

[Razkid 68]

I'm getting ready to remove the engine in my 520H. Can anyone tell me about how much it weighs? Can two people with bad backs lift it?!!

[GMan 82]

Those engines weigh in the neighborhood of 100 to 125 lbs..................................Gary

[Razkid 68]

Thanks Gary. I think I'll have my nephew come over and give me a hand.

[GMan 82]

I wrestle them around fairly often by myself but readily admit I never have been accused of being the brightest bulb in the box. I always seem to find it easier to do it that way than to dig out my engine hoist that near always seems to be at the backmost part of my barn and is "always" buried deeply under stuff at the times I need to deal with my Onan engines! ..........................Gary

[sorekiwi 761]

I dont have data to argue with Gman, but I'm not sure that an Onan weights 100-125 lbs.  Ive lifted them onto the bench myself, and I'm not a big guy.  Definitely lighter than a big block Kohler, if one old guy with a hernia can do it then "2 guys with bad backs" should be fine.

[cleat 4,936]

I do them by myself as well.

 

To help I try and remove as much weight as possible by draining the oil, remove air cleaner and muffler.

 

Slide off the PTO pulley.

 

May be more but you get the idea, every piece you take off first lessens the weight you need to lift.

 

These engines are aluminum so that helps with the weight.

 

[Razkid 68]

Thanks for all of the replies! My brother and his son came over and set the engine up on the bench for me. Now the fun begins!

[Razkid 68]

Well I got the engine up onto the operating table and started to break it down. The front shroud and head came off with no problem but the rear is a different story. The first bolt snapped and a couple of the smaller shroud bolts will only move a few degrees. I sprayed with PB Blaster and walked away for the night. I'll go back today and use some Kroil and let them soak some more! When installing the heads, does anyone use anti-seize on the bolt threads? 

[cleat 4,936]

I use copper never seize on all bolts but the head bolts.

The head bolts I use engine oil on the threads and under the bolt head.

 

If and bolt does not freely spin into the hole then run in a tap to clean out the threads.

 

[Razkid 68]

Thanks cleat. I got the rear head off and while looking at the broken bolt I found a crack running through several fins and ending at one of the head bolt holes.  It doesn't go all the way through the head but I might as well try to find a replacement for it while the engine is out of the tractor. Good news was there isn't much carbon build up in the cylinders. The intake valves have quite a bit of build up on the backside so I'll have to remove them to clean them up. Is this buildup a common thing with the Onan engine? This engine has about 1200 hrs on it.

[cleat 4,936]

Heads seem to pop up on ebay all the time.

 

Cleat

[GMan 82]

Razkid,

 

I have found that carbon buildup on the intake valves of more Onans I've torn down than those that didn't have it....................Gary

[cleat 4,936]

I notice the rust on the exhaust bolts as well. I hope they come out.

One of mine had an exhaust bolt twist off. What a pain that was to drill out of an aluminum block.

 

All of mine now have Stainless bolts well coated in never seize.

 

Edited January 2, 2017 by cleat

[Razkid 68]

Thanks Cleat and Gary. The buildup is oily, also. Since there are no valve seals I guess that's to be expected. I'm only going to adjust the valves so there shouldn't be a reason to remove the exhaust bolts (hopefully).

 

I did find several sets of heads for sale on Ebay. There is one pair from a 10955D and a couple others from 10955G engines. Is there a difference in the heads between years of this engine? I've also sent an email to A-Z Tractor, a site vendor and supporter, to see if he has one for sale. 

[GMan 82]

Razkid,

 

That engine should have valve seals on the intake valves only. Maybe that is the problem. Also, be sure to check valve to guide clearance before going back together with it and never reuse old valve seals. New specs on intake vavle stem clearance is (0.001—0.002 in.) and max wear tolerance is (0.005 in.). New specs on exhaust vavle stem clearance is (0.002—0.004 in.) and max wear tolerance is (0.006 in.). Also be sure to run a valve guide brush through the guides to remove any crud in there. I can't answer for sure about any head differences but it is not likely that heads from the numbers you called out have any difference. I think the letter of the numbers corresponds with the month of manufacture (ref: A = Jan, B = Feb, C = March, etc.) Maybe Boomer will chime in on this...........................Gary

Edited January 2, 2017 by GMan

[Razkid 68]

You're right Gary! I looked at the parts diagram again and found the intake valve seal shown. I'm glad I haven't placed an order yet...seals will go on the list. I don't have a way to check the clearances except for the old wiggle test but will check the stems for wear when they are removed. I was thinking the letters represented the model year? 

[boomers_influence 106]

club

as to the cylinder heads,

it is always best to match the cast #,

170-xxxx.

thank you. boomer

[shallowwatersailor 3,213]

I've had good results with a Ryobi 3/8" impact driver with stubborn head bolts. It doesn't have a lot of oomph but just seems to break them loose with the impact.