Jump to content
Geno

Onan 20 Valve seat problem

Recommended Posts

shorts

Geno,:  the peen the seat in is a patch job on a good day at best, and you should know that after having an automotive repair shop for years.  Take the engine apart and have your machinist repair the right way by replacing the valve seat just like they have been doing for years on all different types of engines from flathead continental industrial engines to state of the art aluminum engines for either production vehicles or specialty engines like an indy car or nascar engine with aluminum head.  

  • Like 1

Share this post


Link to post
Share on other sites
 
ericj

:text-yeahthat:

 

 

eric j

Share this post


Link to post
Share on other sites
 
Geno

Yeah I know, gotta get time to tear it completely down.  I guess I was just hoping a miracle worker with an easy fix would show up.  I was looking for a Scotty on here.   :laughing-rolling:

  • Like 1

Share this post


Link to post
Share on other sites
 
shorts

sorry, no free lunch, you choose fix it right or do a hack job and cross your fingers.

 

My opinion is that the real problem is/was caused by a lack of maintenance keeping the engine clean so it could cool properly

  • Like 2

Share this post


Link to post
Share on other sites
 
decksetter

I don't understand how the lack of cleaning off the screen causes the rear cylinder to overheat and chuck a seat. If this is really the case I am open to this idea, but the guys that have put temp probes on both cylinders have found the front runs hotter than the rear.

I still think valve adjustments are the problem. I've seen multiple Onans work their valves so tight they didn't close completely. Valve doesn't close, nothing holds pressure on the seat. No pressure on the seat going through thermal cycles, it's bound to pop loose.

Share this post


Link to post
Share on other sites
 
Geno

Wonder why it's always the rear valves going out of adjustment and not the front?  :eusa-think:

Share this post


Link to post
Share on other sites
 
cleat

I have 2 520's. One has a 42" deck and does clog up the screen at least partially, You can still feel lots of air coming out the PTO side but I stop it and clean it off anyways at this point.

 

The other has the 60" deck and never does this, Good thing I guess since the 60 deck sure does work the engine harder.

 

According to the manual the oil filter is there for a reason, to get airflow to cool the oil some.

 

Cleat

 

The Onan is a good motor but it never should have made it out of it's intended environment and put into a Garden Tractor, other brands of tractors have had the same failure. Any air cooled engine is susceptible to proper cooling. The Onan is just extremely sensitive. I don't know how many times I have seen people mowing with a 520 or the likes with a Onan and see the grass screen totally plugged up. Most people who bought Wheel Horse's with Onan's in them are not tractor Guru's and all they have on their minds is getting the yard cut. If they do clean the machine off I am sure it was not on their mind that grass might be clogging up the fins or other areas. Like I said the Onan is a good motor and strong, it just should have never made it into a garden tractor application. It should have stayed where it belongs in a nice and clean RV environment. It's really ashame that Toro chose to ignore this problem. It does not take a rocket scientist to see a Onan will suck up enough grass in the first five minutes of mowing to cover the grass screen compared to other motors. They all get some grass sucked up on there but the Onan is one of the worst of the lot. By putting in even more air flow restrictions along with grass build up you have the makings of what we are all finding out, premature failure. It's a shame that something was not done engineering wise to help overcome this. It's a good motor just out of its environment as far as I can see. Now if Geno can fix this Onan, I am sure he will be very alert to what causes this and will take appropriate measures to keep it from happening again and get a long life out of it.

Share this post


Link to post
Share on other sites
 
shorts

It's not so much a cleaning the screen issue as it is the build up of dust and grass on the cooling fins and acting as insulation preventing proper heat transfer and cooling of the jug/cylinder.  remember the oil filter and it's mounting pad change the way that the air flows and creates low pressure/velocity areas where the dirt builds up, the cooling effect on the oil filter is also necessary for engine longevity so if you move it to remote mounting it still needs to be in free flowing air and have long enough lines to act as a cooler. also make sure that the gasket around the filter is in the tins to keep the airflow where it needs to be

  • Like 3

Share this post


Link to post
Share on other sites
 
shorts

valve adjustments = maintenance.

  • Like 3

Share this post


Link to post
Share on other sites
 
km3h

Anyone who has ever removed the tins from an Onan engine after a few hundred hours can tell you that the rear cylinder is packed solid with debris. I wonder if taking temperature readings with a digital meter pointed at the engine is entirely accurate. Remember the engine is covered with the tin and an accurate reading is relative to engine flow. You really are only getting a reading of the outside of the tins. Since the trouble spot is around the valves, that's where the temperature is critical.

After seeing what is accumulated under the engine tins on these engines I have determined that it would be most beneficial to the engine to remove the tins every 100 hours and clean and degrease everything. Sure it is a lot of trouble doing this. but why do we collect these things if we aren't going to tinker with them. A hundred hours of running time is probably three to five years or more in most cases. Seems like a fair price to pay for the sound and power of these engines.

  • Like 3

Share this post


Link to post
Share on other sites
 
Ed Kennell

                                                                                                            :text-+1:  :text-yeahthat: Says  it all.

  • Like 1

Share this post


Link to post
Share on other sites
 
decksetter

Wonder why it's always the rear valves going out of adjustment and not the front? :eusa-think:

No idea, but that's how all mine were. Rear intake valves were held open just a little by the lifter.

Anyone who has ever removed the tins from an Onan engine after a few hundred hours can tell you that the rear cylinder is packed solid with debris. I wonder if taking temperature readings with a digital meter pointed at the engine is entirely accurate. Remember the engine is covered with the tin and an accurate reading is relative to engine flow. You really are only getting a reading of the outside of the tins. Since the trouble spot is around the valves, that's where the temperature is critical.

After seeing what is accumulated under the engine tins on these engines I have determined that it would be most beneficial to the engine to remove the tins every 100 hours and clean and degrease everything. Sure it is a lot of trouble doing this. but why do we collect these things if we aren't going to tinker with them. A hundred hours of running time is probably three to five years or more in most cases. Seems like a fair price to pay for the sound and power of these engines.

Totally agree the crap should be cleaned out periodically. At that point though, you might as well set the valves since you've got it partially apart anyway.

  • Like 1

Share this post


Link to post
Share on other sites
 
km3h

No idea, but that's how all mine were. Rear intake valves were held open just a little by the lifter.

Totally agree the crap should be cleaned out periodically. At that point though, you might as well set the valves since you've got it partially apart anyway.

I got a 416_h last month and the first thing I did was pull the engine, clean it and re-set the valves. It had 525 hours on it, was filthy inside and full of carbon. Intake valve was dead on and the exhaust was off by .001. I am restoring the tractor and just installed the motor yesterday. Started it up for the first time and it sounds terrific. Onan recommends that you do the valves and de-carbon every 500 hours. Still it needs cleaning a lot more than that.

  • Like 1

Share this post


Link to post
Share on other sites
 
JackC

per ekennell:  "BTW, I doubt if a steel seat could be cold pressed into a aluminum bore successfully.  The bore would need to be machined with the correct interference with the seat.   Then a temp differential created so the seat could  be dropped in the bore."

 

If a seat pops out due to the aluminum block overheating, then why can't the same seat be put back in?  I assume the block is still the same and the seat is still the same.  The seat could be put in the freezer to shrink it and the seat area of the block can be heated with a high temp heat gun to expand the seat opening.   With sufficient temp differential you should be able to pop the same seat back in and then avoid the over temp problem occurring again.  Cost of repair is zilch or maybe some time and a head gasket.  Has anyone tried that or know of any reason why that would not work?  I love my ONANs and I plan on trying that on an engine I bought with a popped seat.

Share this post


Link to post
Share on other sites
 
Geno

When you get yours apart you'll see why.  Go back and look at all the pics I posted in here, the problem is not getting it back in.  :eusa-doh:

  • Like 2

Share this post


Link to post
Share on other sites
 

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...