1990Onan520-H 15 #1 Posted November 5, 2018 Hi all, as the title states I'm looking for some advice/tips on what to do with a pair of 520's I just picked up. It seems both may need engines or major repairs. My initial thoughts were to use the 90 to mow and the 91 to snowblow since it has the gear reduction steering and is in worse condition than the 90 in many ways. However I am not sure it will be worth fixing both and maybe I should stick to repairing the 90 and use the 91 for parts or just sell it. I could always swap attachments in the fall/spring and keep one 520 for all duties. I am more of a purist and would really like to keep the factory Onan's, but I'm also open to re-powering suggestions as much as I don't want to do that, as long as it makes sense assuming you think these engines aren't complete toast. The 1990: Little over 800 hours on the meter and overall in halfway decent shape. Runs but not well. Rear cylinder is completely dead. 0 PSI wet or dry so probably a valve issue. Front cylinder fires but is weak, 60psi dry 120 PSI or so wet. As a side note the spark plugs are very fouled and covered in carbon so I can only imagine the cylinders are just as bad The 1991: Little over 1200 hours on the meter and she was ridden hard and put away wet. Has a knocking noise coming from what seems above the hydro and slightly behind the engine, hoping it's not a dropped valve seat. Either way it runs, but rear cylinder is 30psi and the front is 90, wet they come up to 60 and 150. It will only run for about 30 seconds and then cuts out due to loss of spark. I'm fairly certain it is the ignition module behind the flywheel as the coil checks out ok, but I haven't bothered fixing it since it seems it may become a parts donar. Open to any suggestions/input as I know these Onans are getting old and are hard to get parts for from what I am reading. Share this post Link to post Share on other sites
WVHillbilly520H 10,369 #2 Posted November 5, 2018 Pictures would help determine worthiness, I too am an Onan fan when they are running right, not only are the parts harder to find but when you do they are pricey, there's actually a couple guys here on the forum who may be better able to help you with the engines @onanparts.com and @boomers_influence they are the Onan guys, BTW to , Jeff. 1 Share this post Link to post Share on other sites
onanparts.com 178 #3 Posted November 5, 2018 33 minutes ago, 1990Onan520-H said: Hi all, as the title states I'm looking for some advice/tips on what to do with a pair of 520's I just picked up. It seems both may need engines or major repairs. My initial thoughts were to use the 90 to mow and the 91 to snowblow since it has the gear reduction steering and is in worse condition than the 90 in many ways. However I am not sure it will be worth fixing both and maybe I should stick to repairing the 90 and use the 91 for parts or just sell it. I could always swap attachments in the fall/spring and keep one 520 for all duties. I am more of a purist and would really like to keep the factory Onan's, but I'm also open to re-powering suggestions as much as I don't want to do that, as long as it makes sense assuming you think these engines aren't complete toast. The 1990: Open to any suggestions/input as I know these Onans are getting old and are hard to get parts for from what I am reading. Just about any parts you may need are available both new and used, also NOS, New Old Stock. Until you open them up for inspection, minimum of pulling the heads, you won't know exactly what may be required. Share this post Link to post Share on other sites
1990Onan520-H 15 #4 Posted November 5, 2018 13 minutes ago, WVHillbilly520H said: Pictures would help determine worthiness, I too am an Onan fan when they are running right, not only are the parts harder to find but when you do they are pricey, there's actually a couple guys here on the forum who may be better able to help you with the engines @onanparts.com and @boomers_influence they are the Onan guys, BTW to , Jeff. See below thread for pics. Notice the difference in the color of the hoods in the bottom right corner of the picture when they're in the trailer. The 91 obviously spent its life outside... Lots of mower deck rot and patches on the 91 deck also. It's not totally trashed but it's really seen better days. Had it not ran and moved itself off the trailer I wouldn't even have thought about fixing it, but it runs, moves, hydro deck works and the blades spin free. My guess is it sat for the better part of 5-10 years based on the smell of the gas and the green moss growing all over it. I could maybe fix the engine and run it with low compression on one cylinder but who knows if the rings are stuck or what the knocking is, also loses air in the one tire. I can see it becoming a nightmare when I have 2 of them to maintain. It has potential don't get me wrong, I'm just not sure I'm the guy right now because it needs a lot of TLC. Share this post Link to post Share on other sites
1990Onan520-H 15 #5 Posted November 5, 2018 16 minutes ago, onanparts.com said: Just about any parts you may need are available both new and used, also NOS, New Old Stock. Until you open them up for inspection, minimum of pulling the heads, you won't know exactly what may be required. Let's figure worst case the engine needs a full rebuild but the core is good to reuse. As in block, heads, cam and crank. Any idea what it would cost? Can pistons/rods all bearing still be had? I'm one to not half ass anything. I would want a solid running machine to serve me the next 20+ years. Share this post Link to post Share on other sites
SylvanLakeWH 24,175 #6 Posted November 5, 2018 Rebuilds will end up costing you less than some of the new box store junk. Start with one and use the other for parts / spare purposes... 1 1 Share this post Link to post Share on other sites
ericj 1,576 #7 Posted November 6, 2018 3 hours ago, onanparts.com said: Just about any parts you may need are available both new and used, also NOS, New Old Stock. Until you open them up for inspection, minimum of pulling the heads, you won't know exactly what may be required. pull the motors and pull the heads, you won't know what you got till you do. I have had several valve seats repaired / replaced at the local NAPA machine shop for about $ 100.00. So relax you may not be totally into deep yet. My bet would be that the 90 lost a rod and the 91 has valve issues. It could be valves just out of adjustment. If your 9 pins are still in tack and not burnt, you can swap motors fairly easy. good luck eric j Share this post Link to post Share on other sites
1990Onan520-H 15 #8 Posted November 6, 2018 34 minutes ago, ericj said: pull the motors and pull the heads, you won't know what you got till you do. I have had several valve seats repaired / replaced at the local NAPA machine shop for about $ 100.00. So relax you may not be totally into deep yet. My bet would be that the 90 lost a rod and the 91 has valve issues. It could be valves just out of adjustment. If your 9 pins are still in tack and not burnt, you can swap motors fairly easy. good luck eric j Ok apart they will both come. Just have to find some time. How hard are these guys to work on? Anything I should know before just unscrewing stuff? Anywhere I can get a service manual for free? First time working on any kind of tractor. Share this post Link to post Share on other sites
onanparts.com 178 #9 Posted November 6, 2018 5 minutes ago, 1990Onan520-H said: Ok apart they will both come. Just have to find some time. How hard are these guys to work on? Anything I should know before just unscrewing stuff? Anywhere I can get a service manual for free? First time working on any kind of tractor. Service manual in PDF can be downloaded here: 1 Share this post Link to post Share on other sites
1990Onan520-H 15 #10 Posted January 19, 2019 On 11/5/2018 at 8:47 PM, ericj said: pull the motors and pull the heads, you won't know what you got till you do. I have had several valve seats repaired / replaced at the local NAPA machine shop for about $ 100.00. So relax you may not be totally into deep yet. My bet would be that the 90 lost a rod and the 91 has valve issues. It could be valves just out of adjustment. If your 9 pins are still in tack and not burnt, you can swap motors fairly easy. good luck eric j Well finally did some digging. Looks like you're right about the 90 unfortunately. Pulled the valve cover and there's a hole right through the block and the intake valve is jammed open. Crank journal looks pretty scored up too. Is this common with only 845 hours on this machine to throw a rod? Did rods get upgraded in later years? I remember reading something about upgraded replacement rods somewhere. Share this post Link to post Share on other sites
ericj 1,576 #11 Posted January 20, 2019 don't think I've ever seen one blown like that, 7 minutes ago, 1990Onan520-H said: Is this common with only 845 hours on this machine to throw a rod? if the PO didn't do the maintenance on the unit then that's what happens. I worked on a I believe a 93 with only a little over 300 hrs on that threw a rod and cracked the top of the block under the intake and exhaust manifolds. eric j Share this post Link to post Share on other sites
1990Onan520-H 15 #12 Posted January 20, 2019 2 minutes ago, ericj said: don't think I've ever seen one blown like that, if the PO didn't do the maintenance on the unit then that's what happens. I worked on a I believe a 93 with only a little over 300 hrs on that threw a rod and cracked the top of the block under the intake and exhaust manifolds. eric j Any idea about upgraded rods on later years? I was thinking of putting my 91's engine in the 90 because the 90 is in much nicer shape but with how beat up the 91 is I'm not sure it's worth it especially since the 91 could chuck a rod too at any time it seems. Share this post Link to post Share on other sites
ericj 1,576 #13 Posted January 20, 2019 I think the difference came between 89 and 90 in the rods. maybe do some checking on onan parts.com. Might be able to tell a year from the difference in part numbers. Does the 91 knock or make any noise, pull the engine tins and clean the cooling fins. Did you check to see if the valve seat is out or not, or where you were loosing compression ? eric j Share this post Link to post Share on other sites
1990Onan520-H 15 #14 Posted January 20, 2019 2 minutes ago, ericj said: I think the difference came between 89 and 90 in the rods. maybe do some checking on onan parts.com. Might be able to tell a year from the difference in part numbers. Does the 91 knock or make any noise, pull the engine tins and clean the cooling fins. Did you check to see if the valve seat is out or not, or where you were loosing compression ? eric j Haven't gotten a chance to check out the 91 yet, but I don't think the engine knocks. There is a knocking noise on occasion, but it sounds like it's more from the seat area above the hydro. Then again I guess sound travels. The 91 was parked because it will only run for 30 seconds or so Then die, but maybe it was in rough shape before that, im not sure. Share this post Link to post Share on other sites
ericj 1,576 #15 Posted January 20, 2019 1 hour ago, 1990Onan520-H said: Haven't gotten a chance to check out the 91 yet, but I don't think the engine knocks. There is a knocking noise on occasion, but it sounds like it's more from the seat area above the hydro. Then again I guess sound travels. The 91 was parked because it will only run for 30 seconds or so Then die, but maybe it was in rough shape before that, im not sure with the 90 motor in bad shape you can use what ever parts from it that you need to get the 91 running. get the motor running then take the best parts from both tractors and and make one good tractor. use the best sheet metal the best frame and so on. good luck eric j 1 Share this post Link to post Share on other sites