P220 Onan

[oldhorse1 7]

Had the intake port TIG'd to repair a chipped shoulder on the bottom of the valve seat bore in the block itself, as a result of the valve seat coming loose. Need to bore out the excess material and to accommodate the oversized seat I'm going to install. However, without spending some very tedious time, indicating off a pin in the valve guide, and sweeping the block on the cylinder end, I'm wondering if anyone has the spec on the angle at which the valve seat bore is from the cylinder end of the block. I could also square up on the end of the head end of the block, and sweep the face of the adjacent exhaust valve to determine the angle (closely), but would feel more comfortable if I had the spec on the angle, as the block was originally machined, simplifying the set up on the Bridgeport, and me being able to sleep better knowing I used the factory spec, insuring my angle alignment to the valve guide bore.

[WHX?? 48,808]

 

@onanparts.com or @daveoman1966 Know a lot about Onan's so they may be able to help. Would be interesting to see some pics of what you are doing.

[oldhorse1 7]

I'll see what I can rustle up and get some pics, prior to machining, and uploaded for anyone interested. Like I said, the TIG work is done, just trying to nail down the angle specs, as the block was originally machined.

I don't recall ever coming across dimensions/spec angle for machining the valve seat bore in the block.

This is the second seat. Original seat pulled out at about 600 hours, before I installed a .010 over seat. I'm now prepping the block for a .062 over seat, with 1500 hours on the engine. So, I figure, if I got half as many more hours out of the first replacement seat, as I did with the original factory seat, might as well, put in another one. May be the last hoorah, and I'll get whatever it will give me.

Not a thing wrong with the rest of the engine, and I'd really like to mate the engine back on its original frame. I've owned the tractor from new, and just not ready to retire the engine yet, if I can get another 900 or so hours out of it.

 

[oldhorse1 7]

Thanks WHX14 on the contact/consult reference. I appreciate it.

 

[WHX?? 48,808]

Your welcome Old Horse. This subject has been wrestled with many time before here. Most of us get turned off by the cost and start talking about a repower or motor swap of sorts. Sounds like you have a machinist under your wing tho.

[Shynon 7,459]

@boomers_influence

[Ed Kennell 38,071]

 Boomer is the Onan Man.

[Ed Kennell 38,071]

Was it the rear cylinder that popped the seat?

[KC9KAS 4,741]

@oldhorse1 

I have a great amount of admiration for a person that not only has machine shop equipment, BUT can use it properly too! 

[oldhorse1 7]

Yes, same rear cylinder seat, that I replaced at 600 hours with a .010 oversized seat. At that time, there was no casting damage, as there was this time, thus the reason for some TIG work, prior to boring the valve seat bore in the casting out to a .062 oversized seat.

Fortunately, I've got 20+ years of automotive and CNC machining on my resume, just limited on such equipment in my own shop. But do have a nearby neighbor who has as many years in the field, and who graciously provides access to his lathe, a nice old Bridgeport and some other craft and repair equipment ideal for my projects. And it gives us time to chat about what we've worked on in the past. 

I'd be grateful to talk with Boomer on this subject, or anyone who can point me towards machine drawings or specs for the seat bore angle on the block.

[oldhorse1 7]

Like I said in prior post, I don't mind doing it the long, old school way, sweeping an indicator across the adjacent exhaust valve to determine the approximate angle, or put a rod in the valve guide and trig out a perpendicular sweep from the rod, to the end of the cylinder head end of the block. I think that would get me in the ballpark, but a degree off, one way or the other could mean the difference of nailing it, or misalignment of the valve stem to the guide, and ultimately wasting time, money and the opportunity of salvaging an otherwise good engine.

I know a repower job is in the future, and I've got a whole other 520 chassis and running gear minus the engine to replace plenty other parts as needed. But as good as the rest of this engine is, I think I can squeeze another 800-1000 hours out of it.

No smoke, good compression (minus the missing valve seat right now), and uses less than a 1/2 qt. or oil during the entire season, with 1-1/2 acres of mowing, and mostly retired now from snow duties. I have thrown the old moldboard on the back the last couple of years to turn the garden over before running the tiller through it, just for the fun of it. And it tills up nicer.

Again, thanks to all who made the effort to drop suggestions my way. Greatly appreciate it.

[ericj 1,578]

I've had several valve seats replaced by NAPA in East York. They order in over sized valve seats and machine them down to fit the block. As far as I know they don't order genuine Onan seats, they order after market seats. They do also clean the block up as far as I know. I take the a stripped down short block. I don't know if you would call them if they would give you any info or not, might be worth a try. It's the NAPA in Industrial Highway in East York. Good luck

 

 

 

 

 

eric j 

[oldhorse1 7]

Thanks eric j, worth a shot.

[oldhorse1 7]

Thanks to all who have posted comments, thoughts and suggestions on this topic.

All tig weld done on the valve seat counter bore. Machining finished, seat installed, and finished putting the engine back in the 520 today. Sounds good as new.

Special thanks to Boomer for the detailed discussion about the couple of years of questionable casting material in the Onan's, and trading thoughts on my assumptions and calculations on coefficient values of the block and the steel seat.

Having replaced the same seat at 680 hours, with a .010 oversized seat, pressed at .004,  and now again at 1480 hours, I was looking for more resolve, with the intent to wear out the engine before I have to deal with another loose seat. With that, I went with a .007 press fit, and staked the casting around the seat, as a result of calculating the coefficients of both the aluminum block and the steel seat, with some assumption, and the green light from 35 year local master machinist.

As I assembled this thing though, I stewed over why Onan, or any engine designer, would blow air across the engine, across the exhaust port, and then across the intake, and then wrap sheet metal all around it. So in the process of assembling the sheet metal and shroud, I decided to experiment, and made a 1-3/4" hole in the top rear of the flywheel shroud, and the same in the side of the sheet metal shroud that covers the exhaust/intake and valve cover area on the back cylinder. I then acquired a piece of 1-1/2" i.d. flex tube (like you used to see coming off the heat shield on a '60's or 70's model car's exhaust manifold), up to the air snorkel on the air cleaner housing.

I connected the one end into the hole on the flywheel shroud, and the other end into the cover over the exhaust/intake and valve cover area of the rear cylinder, and sealed both ends. After I finished the rest of the assembly, fired it up and left it get to operating temp and then hit it with my heat temp gun. As suspected, the change in temp from the front to the rear cylinder was significant.

Temp checking the block, in the jug area where the intake seat would be, front cylinder = 204F-210F, rear cylinder = 170F-175F. Interestingly though, the intake runners right at the head were both about 220F-225F, which is understandable, given the exhaust pipe passes just above the intake runner.

Exhaust temp, was 325F, on the pipe just above the intake runner on the rear cylinder, which is in the immediate area I installed the 1-1/2" flex tube. The exhaust pipe on the front cylinder, just above the intake runner was ranging 350-355F. All temps taken at 3300 rpm.

I'm considering adding flex tube to the front end of the flywheel shroud, and sending a shot over to the top of the heat shield on the front cylinder (intake valve side). One last note of interest, when idled down to 1200 rpm, within two minutes, rear cylinder temp dropped to 150F-155F, front cylinder only dropped to 189F at best.

Throwing this out there, see if anyone has tried this on any 520's.

Pics attached.

Thanks again to all, look forward to further comments or hearing about your own experiments.

 

[WHX?? 48,808]

Just out of curiosity are you running a cut out  modified belt guard? 

[oldhorse1 7]

No. I have heard others modifying the belt guard. I'm considering having that area of the belt guard louvered, to allow improved air flow, rather than just cutting a section out. (too many grandkids around who like tractor rides and being around tractors) And looks better than just cutting a section of the guard out.

As promised in previous posts for those who had inquired prior to repairs being completed, here are some completion pics of seat    

repair, beginning with the Tig work done on the base of the counter bore which the loose seat chipped a piece out of the block out at the base of the counter bore. Then a shot of the .062 oversized seat installed and staked, and finally a shot with the valve installed.

[WHX?? 48,808]

Eventually will put some edging on the cut section and some hardware cloth or perforated metal for a guard. Then duct it into the cab for winter heat.

[Keith 21]

some have installed a water mist system on air cooled motors that is directed at the cooling fan, not at the fins on the cylinder.  The water evaporates and cools the air.  This system  also helps an oil cooler to be more efficient.

 

http://forums.pelicanparts.com/porsche-911-technical-forum/150982-water-vapor-cooled-911-rubbermaid-solution.html

[Squint_603 0]

On 5/6/2018 at 12:20 AM, oldhorse1 said:

Thanks to all who have posted comments, thoughts and suggestions on this topic.

All tig weld done on the valve seat counter bore. Machining finished, seat installed, and finished putting the engine back in the 520 today. Sounds good as new.

Special thanks to Boomer for the detailed discussion about the couple of years of questionable casting material in the Onan's, and trading thoughts on my assumptions and calculations on coefficient values of the block and the steel seat.

Having replaced the same seat at 680 hours, with a .010 oversized seat, pressed at .004,  and now again at 1480 hours, I was looking for more resolve, with the intent to wear out the engine before I have to deal with another loose seat. With that, I went with a .007 press fit, and staked the casting around the seat, as a result of calculating the coefficients of both the aluminum block and the steel seat, with some assumption, and the green light from 35 year local master machinist.

As I assembled this thing though, I stewed over why Onan, or any engine designer, would blow air across the engine, across the exhaust port, and then across the intake, and then wrap sheet metal all around it. So in the process of assembling the sheet metal and shroud, I decided to experiment, and made a 1-3/4" hole in the top rear of the flywheel shroud, and the same in the side of the sheet metal shroud that covers the exhaust/intake and valve cover area on the back cylinder. I then acquired a piece of 1-1/2" i.d. flex tube (like you used to see coming off the heat shield on a '60's or 70's model car's exhaust manifold), up to the air snorkel on the air cleaner housing.

I connected the one end into the hole on the flywheel shroud, and the other end into the cover over the exhaust/intake and valve cover area of the rear cylinder, and sealed both ends. After I finished the rest of the assembly, fired it up and left it get to operating temp and then hit it with my heat temp gun. As suspected, the change in temp from the front to the rear cylinder was significant.

Temp checking the block, in the jug area where the intake seat would be, front cylinder = 204F-210F, rear cylinder = 170F-175F. Interestingly though, the intake runners right at the head were both about 220F-225F, which is understandable, given the exhaust pipe passes just above the intake runner.

Exhaust temp, was 325F, on the pipe just above the intake runner on the rear cylinder, which is in the immediate area I installed the 1-1/2" flex tube. The exhaust pipe on the front cylinder, just above the intake runner was ranging 350-355F. All temps taken at 3300 rpm.

I'm considering adding flex tube to the front end of the flywheel shroud, and sending a shot over to the top of the heat shield on the front cylinder (intake valve side). One last note of interest, when idled down to 1200 rpm, within two minutes, rear cylinder temp dropped to 150F-155F, front cylinder only dropped to 189F at best.

Throwing this out there, see if anyone has tried this on any 520's.

Pics attached.

Thanks again to all, look forward to further comments or hearing about your own experiments.

 

 

 

Oldhorse, I'm trying to revive your old post. I currently have a P220 (actually a LX790) out of my tractor and sitting in my shop. I need to machine an exhaust valve seat counterbore, as it had been loose and causing significant damage, when run by the PO. I have a replacement valve seat and valve, but even the oversized aftermarket valve seats aren't large enough to make up for the oversized counterbore on my engine. I'll have to machine a sleeve with an interference fit between the engine and the valve seat to make this work.

 

I was wondering if you ever determined the specification for the angle on the valve guide/valve? I will try to reach out to @boomers_influence to see if he had the information to share with you during your repair.  I didn't see it in your final write up. I do have a full machine shop, but would like to know if the OEM spec was available prior to setting it up and measuring like you originally suggested.

 

Thanks!

[lynnmor 7,303]

6 hours ago, Squint_603 said:

 

 

Oldhorse, I'm trying to revive your old post. I currently have a P220 (actually a LX790) out of my tractor and sitting in my shop. I need to machine an exhaust valve seat counterbore, as it had been loose and causing significant damage, when run by the PO. I have a replacement valve seat and valve, but even the oversized aftermarket valve seats aren't large enough to make up for the oversized counterbore on my engine. I'll have to machine a sleeve with an interference fit between the engine and the valve seat to make this work.

 

I was wondering if you ever determined the specification for the angle on the valve guide/valve? I will try to reach out to @boomers_influence to see if he had the information to share with you during your repair.  I didn't see it in your final write up. I do have a full machine shop, but would like to know if the OEM spec was available prior to setting it up and measuring like you originally suggested.

 

Thanks!

I wouldn't use a sleeve around the valve seats, onanparts.com has/had way oversize seats that need machined to fit.  There are other suppliers of valve seats as well, basically you are just buying raw material and machine it to fit.  Boomer might be retired.  The valve angle isn't written anywhere that I could find, I indicated a pin that was a tight fit in the valve guide to get the angle, I should have recorded it but it might be 7 degrees.  You should have .0055 to .0060 press fit, I chill the seats with dry ice in alcohol and heat the block with a heat gun for at least an hour. 

 

I made a tool to fit the valve guide and the ID of the seat so I could quickly tap the seat in.  The tool needs to have some clearance so it doesn't hang up when the temperatures equalize.  Another benefit of the tool is that it is immersed in the dry ice and alcohol and will help keep the seat cold as you install it.  If you work real fast, the seat will go right in, if you hesitate it will tighten up prematurely.

Edited Thursday at 10:58 PM by lynnmor

[Squint_603 0]

On 11/14/2024 at 5:01 PM, lynnmor said:

I wouldn't use a sleeve around the valve seats, onanparts.com has/had way oversize seats that need machined to fit.  There are other suppliers of valve seats as well, basically you are just buying raw material and machine it to fit.  Boomer might be retired.  The valve angle isn't written anywhere that I could find, I indicated a pin that was a tight fit in the valve guide to get the angle, I should have recorded it but it might be 7 degrees.  You should have .0055 to .0060 press fit, I chill the seats with dry ice in alcohol and heat the block with a heat gun for at least an hour. 

 

I made a tool to fit the valve guide and the ID of the seat so I could quickly tap the seat in.  The tool needs to have some clearance so it doesn't hang up when the temperatures equalize.  Another benefit of the tool is that it is immersed in the dry ice and alcohol and will help keep the seat cold as you install it.  If you work real fast, the seat will go right in, if you hesitate it will tighten up prematurely.

Thanks for the quick reply Lynnmor. I did take a look at onanparts.com during my early research for parts. Unfortunately their largest oversized seat (+06") is out of stock. I have an exhaust valve that the counterbore is now .045-.05" oversized and out of round before even machining it to clean it up. With machining and a suitable press fit, even this most oversized valve may not be large enough even if it was in stock. I see they have various intake valve seats (+.100-.120" oversize) but that won't help here.

 

Without knowing the alloy or hardness of the valve seat, I reasoned it was safer to buy a nominal valve seat and install it into a hefty sleeve before installing the two into the block. With essentially the same CTE and interference fit between the sleeve and the stock valve seat (~.006-.007" PF), it should stay secure in the engine block for at least a few hundred more hours. I would finish the valve seat/angle with a carbide reamer and pilot that I ground to match the valve guide this would ensure concentricity and roundness after installation.

 

I know this isn't an ideal repair, but my back is sort of against the wall here. The damage to the block from the valve seat hammering around for a long time really doesn't leave me many options. I know this probably won't extend the life of the tractor by much, but I'm also not willing to throw in the towel on a repair yet. The tractor was a free gift to me a few years ago and I've worked through about a dozen other repairs, trying to keep the budget down for a project tractor. I just machined and welded up a 3PH setup for it shortly before I discovered this valve seat damage. Oddly enough it was a fouled spark plug that led me to discovering it. I pulled the head and valve covers off to discover the intake valve stem seal was allowing oil by. It was burning off  due to high exhaust temps from a non-sealing exhaust valve. And that's when I noticed the extensive counterbore damage.

 

FWIW I did a brief search for a replacement/donor block ($300+ USD on ebay!) and potential repower options, new and used ($1000+ USD!!). A direct swap out would be easiest, although the most expensive. Retrofit of another similarly powered twin may prove to be more effort than it's worth.

 

I appreciate your input, let me know if any other options come to mind before I pull the trigger. The engine is currently fixtured on a machine but I'm not in a rush to free that particular mill up just yet.

 

Thanks!