Thinking about 520H Repower

[WHX?? 48,703]

My understanding is head bolts should be checked & re-torqued after a little run in and when warm. Couple of my Kohlers were very loose after running.

[WVHillbilly520H 10,373]

1 hour ago, WHX14 said:

My understanding is head bolts should be checked & re-torqued after a little run in and when warm. Couple of my Kohlers were very loose after running.

[r1jakecfd 51]

Good point. I’ll run it, let it warm up and retourque. It ran great for about 15 min then got really loud and lost power. New head gaskets on order. I’ll let you know how it works out! Thanks

[WHX?? 48,703]

Just to further educate a Onan wrenching newbie does the motor have to turned to get at the rear jug head?

[r1jakecfd 51]

2 hours ago, WHX14 said:

Just to further educate a Onan wrenching newbie does the motor have to turned to get at the rear jug head?

Yes. There’s no clearance to get at the rear cylinder head if you don’t remove it. Also, it’s a good idea to remove it so you can inspect and clean the mating surface for a good seal.

[Howie 886]

Did not give the aftermarket block a thought when I made the comment. I do know what the ARP stuff is. Guess I could get some from my engine builder friend, he uses something else instead.

Bulds a lot of circle track engines. On these small engines I just use engine oil on the threads and a dab underhead of bolt. And re-torque after a heat soak. Not trying to be a pain.

Edited January 11, 2018 by Howie

[WVHillbilly520H 10,373]

11 hours ago, Howie said:

 Not trying to be a pain.

Same here, just pointing out this is some good stuff to have (or an equivalent) especially with aluminum threads and steel bolts and torque values, kinda like never seize with stainless steel, Jeff.

[onanparts.com 181]

On 1/10/2018 at 9:15 AM, r1jakecfd said:

Good point. I’ll run it, let it warm up and retourque. It ran great for about 15 min then got really loud and lost power. New head gaskets on order. I’ll let you know how it works out! Thanks

The new gaskets might show up tomorrow, Saturday. Monday only if USPS gets lost!

 

Use a High Temp anti sieze on the head bolts. Nickel based is good but the copper stuff is OK too. No anti seize? Motor oil is better than nothing. Torque the bolts to 5 Ft-Lb, then 10 Ft-Lb, then go around again at 14-16 Ft-Lb. Wait a minute or two, go around again and double check the torque. Graphoil gaskets compress when torqued, more so than non graphoil gaskets, and will settle slightly. Have never had to retorque Onan air-cooled head gaskets once done as described. Good Luck!

 

 

[bigplow1 23]

If you want to repower don't be afraid of the vanguard kit from small engine warehouse just put one in a friends 520h runs great mows better he has the 60 deck and is not easy on it he mows for a couple cities around here that people don't mow or move out some of the yards are 12 plus high and it does great will put one on my dad's when the onan pukes I am not a onan fan to temperamental for me I like my 1 lung Kohler k series 

[Cable 179]

On 1/6/2018 at 12:28 AM, r1jakecfd said:

Hi Guys,

The Onan in my 520H was running poorly so last month I took the heads off, decarboned, cleaned/reseated the valves, checked valve seats and reassembled with new gasket set. When installing intake manifold, I realized last year (carb cleaning) I forgot to hook up vacuum line from manifold to gauge. Hooked it up correctly this time and ran great. First blizzard yesterday and started snow blowing. After about 15 minutes the became noticeably louder with less power.

I was wondering firstly if anyone has any idea what went wrong?

Also, I was thinking about repowering with a Honda or Vanguard and would love opinions on which way to go? Also, should I go with an engine or kit and which company? I’m good at fabrication, etc.

 

Thanks in advance!

Happy NewYear

I just pulled a P220G from a 1990 520H.  It had 453 hours on a working hour meter.  I wanted a number of the parts for another restoration.  The engine is listed on the York, PA Craigs List, where you can see it, see compression readings that were taken, and there is a link to see and hear it running. $875.

[r1jakecfd 51]

3 hours ago, bigplow1 said:

If you want to repower don't be afraid of the vanguard kit from small engine warehouse just put one in a friends 520h runs great mows better he has the 60 deck and is not easy on it he mows for a couple cities around here that people don't mow or move out some of the yards are 12 plus high and it does great will put one on my dad's when the onan pukes I am not a onan fan to temperamental for me I like my 1 lung Kohler k series 

 

[r1jakecfd 51]

Thanks, the Vanguard will definitely be my next move. The strange thing that I can’t figure out is that the vanguard costs more as a bare engine but the converted WH Repower is $400 less than a Honda. The Vanguard is just over $1700 from Small Engine Warehouse and I was just quoted $2080 for the Honda GX630 conversion from Repower Specialists. At Northern Tool, the bare Honda is $1200 vs $1450 for a Vanguard. Who knows???

 

[r1jakecfd 51]

12 hours ago, onanparts.com said:

The new gaskets might show up tomorrow, Saturday. Monday only if USPS gets lost!

 

Use a High Temp anti sieze on the head bolts. Nickel based is good but the copper stuff is OK too. No anti seize? Motor oil is better than nothing. Torque the bolts to 5 Ft-Lb, then 10 Ft-Lb, then go around again at 14-16 Ft-Lb. Wait a minute or two, go around again and double check the torque. Graphoil gaskets compress when torqued, more so than non graphoil gaskets, and will settle slightly. Have never had to retorque Onan air-cooled head gaskets once done as described. Good Luck!

 

 

Thanks for all the advice Onan! You hit the nail on the head. I bought the cheap graphoil set which I had never used before. I’ve always used the OEM aluminized gaskets and never worried about re-torquing. New gaskets coming are OEM! I’ll still re-torque after a short run. When I checked the bolts when removing the head the Middle ones were obviously loose. Lesson learned. I’ll be happy to get it back together for more snow duty! Who knows after that... Turbocharger, supercharger, Nitrous (for snowbanks)?!? 👍 Cheers

[608KEB 795]

Edited January 16, 2018 by 608KEB

[r1jakecfd 51]

On 1/9/2018 at 6:34 PM, lynnmor said:

That gasket does look like inferior material.  Do you know if the head is flat?  I don't think you are to use thread locker on the head bolts, usually you use a drop of oil.

 

On 1/9/2018 at 9:27 PM, r1jakecfd said:

It’s a good lesson in buying OEM parts. Material is completely different material, not aluminized. OEM set on order

Lynnmor,

I think the gaskets are the graphoil which I’ve never used. I’ve never had to retorque the heads with the OEM gaskets. The head looks to be pretty flat but having said that, it’s a pretty thin aluminum head with 9 bolts holding it. I’m sure it would have been fine if yours truly had retorqued when warm😁

[lynnmor 7,294]

55 minutes ago, r1jakecfd said:

 

Lynnmor,

I think the gaskets are the graphoil which I’ve never used. I’ve never had to retorque the heads with the OEM gaskets. The head looks to be pretty flat but having said that, it’s a pretty thin aluminum head with 9 bolts holding it. I’m sure it would have been fine if yours truly had retorqued when warm😁

 

If you have no other way to check flatness, try holding the heads together and check how much feeler gauge you can get between them.  The spec is .004" maximum, so theoretically  that would be a maximum of .008" allowed.  Obviously this is just a rough check because there is no way to say which and how much each head is out, but if .008" goes in then they certainly need to be corrected.  If you have a known flat surface, simply check each with a .004" feeler gauge.  Also if you have that known flat surface, a head can be lapped on a piece of good 240 grit sandpaper.  While I have granite surface plates and wouldn't abuse them, I find that my DoAll saw table works fine for lapping.

[r1jakecfd 51]

On 1/17/2018 at 7:14 PM, lynnmor said:

 

If you have no other way to check flatness, try holding the heads together and check how much feeler gauge you can get between them.  The spec is .004" maximum, so theoretically  that would be a maximum of .008" allowed.  Obviously this is just a rough check because there is no way to say which and how much each head is out, but if .008" goes in then they certainly need to be corrected.  If you have a known flat surface, simply check each with a .004" feeler gauge.  Also if you have that known flat surface, a head can be lapped on a piece of good 240 grit sandpaper.  While I have granite surface plates and wouldn't abuse them, I find that my DoAll saw table works fine for lapping.

Heads look good. I didn’t take the R head off. It has 90+ psi. I retorqued those bolts and reinstalled a new gasket on the L side. Will keep you updated on the test run.

[r1jakecfd 51]

Well guys, gasket installed, ran it to warm it up and retorqued. It sounds great and pretty quiet too! I have a bad voltage regulator so haven’t fully reinstalled yet. I need to add a fuse block as the last person didn’t see the need for fuses🤣. I mean, I’ve never heard of anything shorting out on our beloved horses!😂 I’m going to buy some LED bar lights and an amber led Lightbar for snow duty too.🌬❄️

[Desko 607]

The repower in my opinion isn't worth it. You can have your onan rebuilt for right around $1,200 with all new oem parts not including machine work but are here its $70 to bore them and $25 to cut and grind the valves and seats which imho isn't bad for a smooth running engine. I've seen them go to 5,000 hours in welder gen sets running WOT. Keep the screen clean and blow out the fins with an air gun when you're done they'll go forever. Glad you got her fixed though and she's running good!