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Onan+Rebuild=$$$$$$$$$$$

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IROC-Z28

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Discussion starter · #1 ·
Hi all,
I was just looking at 318's today and wondering to myself why eveyone seems to like the onan engines. According to what I've read (This is only what I've heard) the onans are good for about 1500 hours before they really... really need a rebuild. So I though alright I could deal with that if I had to. Rebuild kits couldn't run me less that $250.00. Wrong, $995.00 for a rebuild kit. Seriously? What engine is ever worth that? I could see that rebuild kit if the engine was likley to get a t least 3000 hours out of it but for a measly 1500 hours and then another rebuild. What Gives? Just courious, don't mean to offend any 318 or 316 owners out there but couldn't help but wonder.

DacMan
 
#2 ·
Most guys don't rebuild, DacMan. SEW has a few Onans in stock for around $1700. You can also get a Honda, Vanguard, or Kohler Command repower kit for the same price.

If they are an absolute purist, they might well pony up as much as the $995 for a kit.

As for hours, I don't know about 1500. My neighbor is over 2000 on his original engine.

As for the design, they are very torquey, and have a tremendous cooling system. You'll do things without lugging the engine that you would not consider with anything comparable.

As for the price, they are popular, so the houses which still support them can pretty much charge what they like. Just like a classic anything else.

I'm a relative 318 newbie, but if my engine popped tomorrow, I would not blink at dropping $1700 on a repower.

Ask yourself why anyone would spend big bucks restoring or buying a restored 65 Mustang and I think you have your answer.
 
#3 ·
Don't know about Green Onan's, but on Case/Ingersoll, we expect to get 3000 hours out of a properly maintained Onan! Yes, rebuilding them is expensive, but that level of torgue is hard to find, and getting another 3000 hours will take it to the next generation, in most situations!

:thThumbsU
 
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Discussion starter · #4 ·
Wow,
I never knew they could go so long. Just curious what makes them so "tourquey" compared to any other two cylinder 18 h.p. I have heard this from everyone so something must be special.

Thanks, DacMan
 
#5 ·
Last year I drug two Onans out of the scrap heap at local scrap yard. Bought for cheap, both 70's vintage & can tell never been into. Took heads off, cleaned loose carbon out, new plugs, cleaned carbs, and points cleaned/adjusted. Both run like a top & not more than spark plugs & oil as expense. re-used the head gaskets too. These engines have untold hours on them & ready for more.....tough engines. I just mounted one of these on my MF1655 project. She fires right up & ready to go! One of the sweetest sounding engines there are!
 
#6 ·
Boxer engines are torquey by design. Some hopped up VWs used to beat V-8s back in the 60s in one on one drags. BMW motorcycles can pull huge loads, and off-road very well. Porsche? Do I even need to go there?

The old boxer Briggs were pretty darn torquey too. They all didn't have pressurized oil systems so they didn't necessarily last forever.

As far as longevity on any engine:
Maintenance, Maintenance, Maintenance.
Warm it up before applying a load.
Operate at the designed RPM, not pulling a load at idle - use your hydro or tranny to regulate speed.
Cool it down when you're done (by letting it air cool at high RPM, not at idle). Idle it just before you switch it off.
Avoid starting the engine for 30 seconds just to move it around the shed.
Use Stabil or similar fuel preservative when you store it.
Don't mow "just one more time" knowing you need to have an oil change, filter change, or carb rebuild.
 
#8 ·
Those Onan's have some cooling shrouds on them, that collect dirt behind them. Clean the engine good occasionally. Keep that dirt from plugging up the cooling fins.

Another fellow I was reading put forth the theory that carbon build up in the cylinder gets thick enough that the piston starts hammering against it and eventual breaks a rod. He was pulling the heads and cleaning that carbon off from time to time.
 
#9 ·
Carlos said:
Those Onan's have some cooling shrouds on them, that collect dirt behind them. Clean the engine good occasionally. Keep that dirt from plugging up the cooling fins.

Another fellow I was reading put forth the theory that carbon build up in the cylinder gets thick enough that the piston starts hammering against it and eventual breaks a rod. He was pulling the heads and cleaning that carbon off from time to time.
Click to expand...
The owners manual tells you that, as part of the regular maintenance!:fing20:

Why is it that people do not read the "owner's manual???":banghead3
 
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Discussion starter · #11 ·
I am no expert but I am well educated on maintenance and understand how to. I just had heard some false rumors that Onans were boat anchors after 1500 hours obviously wrong. Just curious one more question,the 318's don't have locking diff's do they?

Thanks for the Info, DacMan
 
#16 ·
I don't know - I use mine in split mode all the time and they still look good. The brakes on our 1938 Allis Chalmers B had to be replaced in the mid 1980s after just 50 years of that kind of abuse.
 
#18 ·
The $995 kit is for an engine that has been overhauled several times or has very high hours. 3000-5000 hours can be expected from an engine that is well cared for before it's time for an overhaul or rebuild.

Dirty oil and filters will shorten the life of any engine!

In many cases an overhaul can be done for a few hundred dollars in parts if you do the job yourself. Best scenario all moving parts are within specs; pistons, rods, bearings, crank etc. In that situation a basic top end job will do. Fresh set of rings and a valve grind and put it back together with new gaskets and seals.

Parts that hold up extremely well on Onan twins are the cam, lifters, oil pump, valves & valve guides along with the main bearings. Valves on the "B" series engines are typically good for at least 2-3 regrinds. The "P" series valves don't have as much meat on them and are good for 1-2 regrinds.

Pistons: In a properly cared for engine they will last many thousands of hours.
Dirty oil and not changing it regularly will gum up the oil control rings and they won't be able to keep the oil inside the motor very well. Dirty air will act as an abrasive and wear out the compression rings, pistons and cylinders. The top compression ring groove will be the first to wear out on an abused engine or one with lots of hours on it.

The upper ring will have excessive up and down movement in the groove and the compression gases will not be able to stay behind the ring and force it out to seal against the cylinder wall resulting in a loss of power. At some point the slop in the ring groove can cause the ring to break and wear a deep nasty spot in the cylinder wall. If not caught soon enough the block will become scrap unless it cleans up at the last oversize available, +.030"

Con rods:
The big ends hold up well. It's the small or wrist pin end you have to keep an eye on. Carefully clamp the rod in a vise with the piston able to move freely and try to move the piston both directions it should not be moving in. Normal piston movement is like nodding your head up and down. Abnormal piston movement is like tilting your head left to right. If you can "see" visible left to right movement the small end of the rod is worn.

Even if your pistons and rods are worn out you are still going to be right around $500 or so including gaskets and seals. Toss in new bearings and you end up closer to $600

So the average range to get your Onan back to like new is $200-$600 for parts. A trip to the machine shop for boring and a crank grind will push the total towards the $750 range. Many of these Onan engines have been working hard for the last 25-35 years for a reason. They are made to last and be overhauled/rebuilt many times.

Note: Onan stopped making these engines several years ago. They never stopped manufacturing the replacement parts you need to make them like new again as of the date of this post, March 2009.

TJ
 
#19 ·
Once agean, thanks for your input Onanparts!!!!

I think the bad rap these engines get as far as cost is from the fact that there is almost no aftermarket suport for them. You need internal parts, you need to get OE. Unlike the old Kohler K singles, that has a HUGE aftermarket. I bet you find that if you used all OE parts, a Kohler single rebuild would not be a whole lot cheaper then the Onan twin.
 
#20 ·
This thread delivers!

I was just wondering yesterday what would be the purpose of split brakes like I have on my 300. Reading this answered my question. I have more, but don't know where to begin, so could anyone highlight this for me some more, such as when and where to use them and maybe a quick little how? Mine just have the little keeper flipped over so both brake at the same time, but more or less I have just been using my transmission to slow and stop.

:thanku:

~F~
 
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art stiverson
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