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So today among other tasks on my new 420, I was removing the valves on the Onan P220G in preparation of lapping the valves. I started on the right hand cylinder first. First thing I did was make sure there were no holes large enough for a valve lock to fit down into. Nope, no big holes, so after compressing the valves springs, I popped the valve locks out with my tiny screwdriver. No problem. Next I did the left side. I ASSUMED that the oil drain hole would be the same size as the one on the right side. So I didn't check. Unbeknown to me, lurking out of sight, hidden by the valve spring, Onan decided to put a GIANT oil drain hole RIGHT UNDER the valve locks!! Really Onan? Really? If you have to have that hole there, how about a coarse SCREEN OVER THE HOLE??? So now I'm going fishing in that hole with a small magnet on a wire.... I know how this is going to end. I'm going to have to rip the engine out of the tractor, and completely disassemble it to get the freakin valve lock outa there.
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That sucks, good luck.
 
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not good, recently did something similar on b43g dropped keeper down hole that went into timing cover, cost me sometime but mine wasn't quite as big deal I just had to back track im just putting mine back together. good luck, stay positive.
 

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Systech,

The CTM2 engine manual for the Onan as used in the Deere tractors specifically advises against lapping the valves!!!

265136


265137


Do you have this manual?

Chuck
 

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How about trying to flush it out with the oil? Do it a few times, even if you have to tilt the tractor over on its side in various directions. Give it a real good flush - never know, it might work and you could also fish in from the oil drain. I'd give that about 1-2hours of my time before I gave up on it I think
 

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Systech,

The CTM2 engine manual for the Onan as used in the Deere tractors specifically advises against lapping the valves!!!

View attachment 265136

View attachment 265137


Do you have this manual?

Chuck
Learn something new every day. I have never seen this in any other engine manual used in any application I've worked on. Leave it to Onan! One of the reasons for lapping is to assure the seat is hitting the center of the valve face. Amongst other good reasons Onan doesn't feel is necessary. I would lap em!

But I would like to hear from Onan their reasoning for this. Which came first? The manual or the short valve life they are trying to avoid? Are these engines even known for short valve life? "Shorter" than what?
 

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Joe,

Not sure of Onan's/Deere's entire reasoning on this matter. The illustrations above are from Deere manual CTM2. From the Onan Performer engine manual 965-0762 we have this:
265140

Notice the language here is "eliminating the need to lap the seating surfaces" and is not quite as firm a statement as the Deere manual content. Would be interesting to get David's or Boomer's take on this from their decades of engine rebuilding on a wide variety of engine types.

Chuck
 

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Joe,

There seems to be lots of discussion on lapping (pro and con) on other discussion groups, here is one that I found very interesting (sorry for the length...) Italics and underlining added by me...

Posted by “Pumaracing” in an engine rebuilding discussion group on PistonHeads.com

Valve lapping is quite a curious engineering process which of necessity I've studied in detail over the years. Prolonged lapping, especially with coarse paste, actually makes the seating surfaces of the valve and head insert concave so the two only make contact on their inner and outer edges. This is obviously very bad for heat dissipation as well as airflow. I can see the effects of heavy lapping very clearly on my valve refacing machine or head seat cutting machine as the grinding wheel or cutter makes initial contact with the concave faces and only touches them along the edges.

You can also easily see the concavity on a valve after prolonged lapping by putting a high quality straight edge across the seat and holding it up to the light. Try it on an old head some time. The mechanism at work here is that the paste on the inner and outer edges of the contact area quickly squeezes out as you start lapping leaving most of the abrasive action taking place along only the centre line of the seat. So lapping can't restore a badly cut or badly worn seat properly as they used to think in the olden days. It might have sufficed for a 30 bhp per litre truck engine from the 1940s but is not what you want for today's high performance machines generating much more heat which needs dissipating properly through surfaces in perfect contact with each other.

However a very light lap with fine paste for just 10 seconds or so to check that the valve and seat are truly concentric and with no high or low spots is a good idea and not a problem. If there isn't an even grey contact area all round both valve and head seat after that then it's probably time for remedial machining rather than further lapping.

For many years now I've used special diamond grit based paste rather than the normal carborundum grit paste you get in little tins with two lids for coarse and fine at each end from car accessory shops. It's horribly expensive but it has a completely different abrasive action which I can't really describe but it's much nicer. Being so hard and sharp, diamond grit abrades the surfaces really fast before the paste has had time to squeeze out and the grit particles don't break down into powder immediately like carborundum does so you don't get the concavity and it takes less time to check that the surfaces are making good contact. However the fine paste from those little tins is perfectly ok for general use. The coarse paste is a definite no no.

I used to have a customer in the early 90s for whom I did the CVH heads for his race car along with many other people's. They generally got a quick refurbish mid season and it took me a while to work out why every time I recut the seat on one of his valves (but no one else's) they were badly concave and only touching the grinding wheel on the inner and outer edges. After speaking to him it turned out that every time I sent a finished head back, despite my own quick lapping to check the seats were perfect he'd stand there for half an hour grinding them in further before assembling everything thinking he was contributing to the general cause and doing some good when in fact he was just buggering up my delicate machining work. After actually showing him what his tinkering had been doing to the concavity of the seats there was one of those "oh sh*t what have I done?" expressions on his face and he left things well alone after that.

In OE engine production valve seats are never lapped which would be horribly time consuming to do on every engine but of course there are constant quality control checks being carried out to make sure the valve and head seat surfaces are being machined to a perfect specification. They also sometimes use a very slightly different angle on the seat in the head and the seat on the valve, maybe half a degree or so, to make the two components "hammer" into full contact after the engine is first started. Not my idea of perfection engineering really. Unfortunately you can't just assume that Joe Bloggs your general engine reconditioner is even capable of cutting proper valve seats which most aren't in my experience so checking them with a quick lap is essential. The much vaunted Serdi machine which is the popular choice these days is a bugger for cutting non concentric seats in the head if there's even a fraction of a thou of valve guide wear. I prefer seat cutting systems with fixed rather than rotating pilots like the Sunnen system.
 

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I think valve lapping originated way back in the 30's when many "tractors" were made from model T's and A's they were no longer usable on the road...for whatever reason! (I think they were referred to as "doodle bugs", but not sure) No compression usually meant one of two things, bad rings or bad valves. Money was tight and many farms were far from civilization so the farmer did his own back yard repairs. If bad rings, simply hone and install oversized rings...pistons may slap around some, but they'd seal (for a while!). Valves & seats were lapped. As long as they found a gray ring (from lapping) around the valve and seat, they were good. If the valve happened to be REALLY burned or bent, just lap more! Not uncommon to have to grind the end of the valve stem because the valve went too deep into the seat and tappets couldn't be set.... just put'em on the bench grinder and, 'There, that looks kinda square." After the Depression, WWII and into the 50's, the process was still used. And in the 50's with the overhead valve engines, you didn't have to grind the end of the valve stems!

My personal thoughts are LIGHT lapping is OK, as stated in the above underlined statement. I would think that more than 10 seconds would be needed though! Lapping will produce a gray ring were the lapping compound removes metal between the 2 surfaces (valve & seat). Once this ring is completely around both the valve and the seat, lapping should be stopped, whether the ring is 1/32" or across the complete face of the seating surface. If the lapping results in a sharp edge on the valve, simply scrap the valve! The sharp edge will quickly heat up and either burn away or warp the valve head, although a bench grinder could be used to grind the specified 1/32 flat!

Lapping is an OK procedure for quick backyard repairs, but interference angles through grinding is the correct and longer lasting procedure. Again, just MY thoughts. Bob
 
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Nor will I join the ranks of intrepid lappers. @systech, all the best with retrieval. A good magnet could just do it, no? Keep us posted

@rwmeyer , I’ve quickly learned that your posts add a lot to the conversation! Very informative, thanks for taking the time.
 

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Back to the original post, I watched a YouTube video by Mustie1. If my memory serves me right, he removed the pto and cover under it, and with magnet, fished a keeper out of a 318. Not sure if it's less work than pulling the engine. Pto on a 420 may be more complicated. Good luck.
 

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Joe,

There seems to be lots of discussion on lapping (pro and con) on other discussion groups, here is one that I found very interesting (sorry for the length...) Italics and underlining added by me...

Posted by “Pumaracing” in an engine rebuilding discussion group on PistonHeads.com

Valve lapping is quite a curious engineering process which of necessity I've studied in detail over the years. Prolonged lapping, especially with coarse paste, actually makes the seating surfaces of the valve and head insert concave so the two only make contact on their inner and outer edges. This is obviously very bad for heat dissipation as well as airflow. I can see the effects of heavy lapping very clearly on my valve refacing machine or head seat cutting machine as the grinding wheel or cutter makes initial contact with the concave faces and only touches them along the edges.

You can also easily see the concavity on a valve after prolonged lapping by putting a high quality straight edge across the seat and holding it up to the light. Try it on an old head some time. The mechanism at work here is that the paste on the inner and outer edges of the contact area quickly squeezes out as you start lapping leaving most of the abrasive action taking place along only the centre line of the seat. So lapping can't restore a badly cut or badly worn seat properly as they used to think in the olden days. It might have sufficed for a 30 bhp per litre truck engine from the 1940s but is not what you want for today's high performance machines generating much more heat which needs dissipating properly through surfaces in perfect contact with each other.

However a very light lap with fine paste for just 10 seconds or so to check that the valve and seat are truly concentric and with no high or low spots is a good idea and not a problem. If there isn't an even grey contact area all round both valve and head seat after that then it's probably time for remedial machining rather than further lapping.

For many years now I've used special diamond grit based paste rather than the normal carborundum grit paste you get in little tins with two lids for coarse and fine at each end from car accessory shops. It's horribly expensive but it has a completely different abrasive action which I can't really describe but it's much nicer. Being so hard and sharp, diamond grit abrades the surfaces really fast before the paste has had time to squeeze out and the grit particles don't break down into powder immediately like carborundum does so you don't get the concavity and it takes less time to check that the surfaces are making good contact. However the fine paste from those little tins is perfectly ok for general use. The coarse paste is a definite no no.

I used to have a customer in the early 90s for whom I did the CVH heads for his race car along with many other people's. They generally got a quick refurbish mid season and it took me a while to work out why every time I recut the seat on one of his valves (but no one else's) they were badly concave and only touching the grinding wheel on the inner and outer edges. After speaking to him it turned out that every time I sent a finished head back, despite my own quick lapping to check the seats were perfect he'd stand there for half an hour grinding them in further before assembling everything thinking he was contributing to the general cause and doing some good when in fact he was just buggering up my delicate machining work. After actually showing him what his tinkering had been doing to the concavity of the seats there was one of those "oh sh*t what have I done?" expressions on his face and he left things well alone after that.

In OE engine production valve seats are never lapped which would be horribly time consuming to do on every engine but of course there are constant quality control checks being carried out to make sure the valve and head seat surfaces are being machined to a perfect specification. They also sometimes use a very slightly different angle on the seat in the head and the seat on the valve, maybe half a degree or so, to make the two components "hammer" into full contact after the engine is first started. Not my idea of perfection engineering really. Unfortunately you can't just assume that Joe Bloggs your general engine reconditioner is even capable of cutting proper valve seats which most aren't in my experience so checking them with a quick lap is essential. The much vaunted Serdi machine which is the popular choice these days is a bugger for cutting non concentric seats in the head if there's even a fraction of a thou of valve guide wear. I prefer seat cutting systems with fixed rather than rotating pilots like the Sunnen system.
I hope I didn't start all of this lapping thing with my post. When I was taught, way back in the 60's, the purpose of lapping valves was not to remove metal or seat valves beyond what the machining would do. It was to check where the seat and valve was making contact and the width of the contact area. Which would be the center of the valve face or wherever the engine specs called it out. Never was it taught to use excessive amounts of compound or more than just a few back in forth movements. Just enough to show the seat pattern.

I have never heard of using lapping compound to correct a bad seating valve or a replacement method to machining. Although I'm sure some do. Or to use it so excessively to cause any of the issues mentioned. That would ridicules'! Proper lapping would remove no more material than buffing out a wax job.

As for never seeing valves lapped on a modern engine produced in todays cars? Who has multi million dollar precision machines in their garage or for that matter, local machine shops. There is absolutely nothing precision about the equipment commonly used to reface valves and seats in most machine shops. They are good, but the results still need to be checked and I know of no other way to do that besides lapping.

In aircraft engines it is still the method of choice as these cylinders do not have removable heads. You have to work thru the bottom of the barrel. Nothing will burn an air cooled engines valves quicker than an improper seat. The proper contact area is essential to valve cooling especially the exhaust as the surface contact area is where most of the heat is dissipated. And I might add, these engines are very similar to our beloved air cooled Onan's and Kohler's. Almost the exact same design, only ten time larger. Except as mentioned the head is integral to the cylinder. This method is still called out in the FAA aircraft powerplant courses and license exams. At least back in the day when I took mine. That would be some time ago!

So, my question was why Onan felt it necessary to inset that remark in the engine manual. I guess I now know. Apparently there are few mechanics who know why and how lapping was ever intended.
 

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Very exact valve to seat patterns can be obtained w/ an extremely thin spot film of Prussian Blue ( available at most real auto parts stores) in a few places on valve face. Bring the valve down w/ a slow swirling action ,in one direction, as you touch seat. Swirl a 1/8 turn while in contact w/seat. Lift away still swirling. (Sorta like touch & go flying). Then visually analyze result to determine course of action, if needed. David
 

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Very exact valve to seat patterns can be obtained w/ an extremely thin spot film of Prussian Blue ( available at most real auto parts stores) in a few places on valve face. Bring the valve down w/ a slow swirling action ,in one direction, as you touch seat. Swirl a 1/8 turn while in contact w/seat. Lift away still swirling. (Sorta like touch & go flying). Then visually analyze result to determine course of action, if needed. David
I like the touch and go analogy. Although not everyone here would understand that either. I've used bluing from time to time. Either way, the point is the purpose of lapping. Not a cheap valve job, but a test, more or less of the finished product. Bluing or compound, it's still called "lapping". (At least by us older folks) Its the technique or process, not the material used. But hell! In today's society who knows what the hell anything means anymore?
 

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(At least by us older folks)
I saw somewhere that we are considered in the Middle age group until we reach 85. So who is actually the older?
 

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In my book that's anyone who knows what a carb looks like and can adjust one...but mileage varies I guess, in my case it's acres.
Jeeze thanks for aging me more than a couple decades. Lol 😂 (can’t say I can adjust a carb in my sleep, but give me the manual and it should work fine after I’m done... ...hopefully)
 

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I saw somewhere that we are considered in the Middle age group until we reach 85. So who is actually the older?
Middle aged in our minds perhaps. Until you take a long look in the mirror or add up the Ben Gay bills. But 85 sounds good to me. Just hope the next ten goes a bit slower than the last.
 
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