Basic 8N Valve Job Questions

I am doing my first valve job on an 8N. I have all the valves out and I am trying to decide if I should replace any parts.

I have owned this 50 side mount for 25 years and have done nothing to the engine. So it is time. The engine lost compression 95 95 70 70 from 1 to 4.

I pulled the head. Could not see anything that was bad to me, but I don't have the trained eye. But the bottoms of the intake valves do not shine like the bottom of the exhaust valves. The intake ports are black. Whether it is oil or exhaust I can not tell. But to me they should be clean and not black

I plan on lapping the valves. But not sure if this is the right plan.

With all that said, my questions are:

1 - Should I replace the valve guides and valves. There is a very very small amount of play between the valve and the guide. Should there be NONE?

2 - Should I replace the springs? I don't know if these are original. They are green. The replacement ones I see are not green. So I assume these are original and if so, they are 60 years old.

3 - Do keepers get worn?

Thanks in advance

Obie

Do you have the split or one piece guides? It sounds like the intake valves have too much clearance thus letting some extra oil past the stems. The springs should be tested if any doubt on their condition exists. The man that trained me 55 years ago said "forget about lapping valves" and I have found that to be a good policy. With that being said and if new guides are installed how are you going to resurface the seats for all the valves? How good is your oil pressure? Have you though about taking the engine out and doing a complete overhaul? We used to have a lot of customers that got the valves ground one year and this improved compression and also increased oil consumption, But this was with tractors with overhead valves. The next year they would schedule a complete overhaul.My 2 cents worth.

I have one piece guides. My valves also rotate. I guess that is in the tappets. So do you think this engine has been worked on?

I put a micrometer on the stems and the guides and it shows no difference.

The oil pressure is good when cold, but will lower when engine warms

I have a friend who is a very good old school mechanic (rebuilds engines and trannies for a living). He told me to pull the valves and he would stop by to grind the seats and the valves. I thought lapping would be fine because I didn't want to bother him. Based on what you are telling me, I am going to bother him.

As far as rebuilding, I didn't tell you the whole story. When the compression got real bad in the summer, I decided to buy another 8N before I got into this project. I can not afford to be down because I cut 4 acres and needed a new machine immediately.

So this 8N, I will be selling. So if I can get the compression up to where it is very accepatible, I will have a clear conscience when I sell it.

Lapping the valves takes very little time and is
useful as a test to see how well the valve and
seat fit together. If nothing else, this
information will be useful to whoever is
regrinding the seats, if you end up doing that.

There will always be a little looseness in the
valve stems because they need a little clearance
to keep from sticking. Careful measuring with
precision tools is necessary to determine if they
are worn beyond limits.

If the valve seating looks good with a little
lapping, I doubt that your compression loss is
from the valves.

Oil leaking past the intake stems can be made
worse by old, hard, or damaged rubber seals. Were
there any rubber seals on the intake valve stems
or guides? New intake valve seals may help the
problem.

If this is the engine that you are considering
boring and resleeving, it would be wise to do a
proper valve job if you go back to sleeves. If you
decide to run the tractor with just a ring job,
only do what valve work is necessary to fix
leaking compression and new seals on the intake
valves. That way if you have to go back into the
engine soon, you can then do the whole job right
at one time.

The valve springs are probably good, but since you
have them apart, and springs are so cheap, why not
just replace them?

Report back on how the valves and seats tested
out.

There is no rubber on my intake or exhaust valves. I guess the originals had rubber and replacements do not?

The intake valve guides should have a rubber seal
that sits in the groove on the outside of the guide
and seals it against the bore in the block. The
seal is part number 8BA-6571. There are no seals
on the exhaust guides, since there is no suction in
the exhaust system to draw oil past the guides.

(quoted from post at 15:25:28 12/02/12) I am doing my first valve job on an 8N. I have all the valves out and I am trying to decide if I should replace any parts.

I have owned this 50 side mount for 25 years and have done nothing to the engine. So it is time. The engine lost compression 95 95 70 70 from 1 to 4.

I pulled the head. Could not see anything that was bad to me, but I don't have the trained eye. But the bottoms of the intake valves do not shine like the bottom of the exhaust valves. The intake ports are black. Whether it is oil or exhaust I can not tell. But to me they should be clean and not black

I plan on lapping the valves. But not sure if this is the right plan.

With all that said, my questions are:

1 - Should I replace the valve guides and valves. There is a very very small amount of play between the valve and the guide. Should there be NONE?

2 - Should I replace the springs? I don't know if these are original. They are green. The replacement ones I see are not green. So I assume these are original and if so, they are 60 years old.

3 - Do keepers get worn?

Thanks in advance

Obie

Click to expand...

All of those things wear and I flat out gaurantee you after 25 years every one of your parts is worn and/or fatigued to some degree. At the risk of getting flamed - just spend the $120 and replace everything . Do you think a commercial engine rebuilder like Jasper, ATK, or even the little guy supplying NAPA with remanufactured engines re-uses valves, guides, or springs? I know Jasper and ATK don't and if NAPA's supplier does I won't be buying one from them.

TOH

Here is a picture of one of the intake valve assembly. There is NO RUBBER SEAL on the valve guide. To me the seal should be on the widest groove which is near the top of the guide.

I do not think it has been a problem for 2 reasons. 1 - These things were pretty darn tight to get out. I think it was sealed. 2 - the top part of the guide is dark where oil/gas/exhaust worked its way down. But below where the seal belongs, the metal on the guide is beautiful and shiny.

Also, look at the intake valve. I think it looks pretty dirty. The exhaust valves and seats look much better and have a metal shine to them.

Would this dirty intake valve be a reason for lost compression? How bad do they have to be to lose compression?

TOH,

You are right. I either grind the valves only to save money or spend the measly $120 to replace everything.

My question is if I replace all, can I leave the valve seats in place and have them ground down or do I need to replace the seats as well?

(quoted from post at 22:55:28 12/02/12)
TOH,

You are right. I either grind the valves only to save money or spend the measly $120 to replace everything.

My question is if I replace all, can I leave the valve seats in place and have them ground down or do I need to replace the seats as well?

Click to expand...

Take the block to a machine shop and let them decide which ones are grindable and which ones need to be replaced. Last I checked new seats are cheap.

If you do not have adjustable lifters setting the valve clearance will be an issue. Now is the time to upgrade to adjustable lifters - probably as much or more more than the valve parts.

TOH

(quoted from post at 01:41:32 12/03/12)

(quoted from post at 15:25:28 12/02/12) I am doing my first valve job on an 8N. I have all the valves out and I am trying to decide if I should replace any parts.

I have owned this 50 side mount for 25 years and have done nothing to the engine. So it is time. The engine lost compression 95 95 70 70 from 1 to 4.

I pulled the head. Could not see anything that was bad to me, but I don't have the trained eye. But the bottoms of the intake valves do not shine like the bottom of the exhaust valves. The intake ports are black. Whether it is oil or exhaust I can not tell. But to me they should be clean and not black

I plan on lapping the valves. But not sure if this is the right plan.

With all that said, my questions are:

1 - Should I replace the valve guides and valves. There is a very very small amount of play between the valve and the guide. Should there be NONE?

2 - Should I replace the springs? I don't know if these are original. They are green. The replacement ones I see are not green. So I assume these are original and if so, they are 60 years old.

3 - Do keepers get worn?

Thanks in advance

Obie

Click to expand...

All of those things wear and I flat out gaurantee you after 25 years every one of your parts is worn and/or fatigued to some degree. At the risk of getting flamed - just spend the $120 and replace everything . Do you think a commercial engine rebuilder like Jasper, ATK, or even the little guy supplying NAPA with remanufactured engines re-uses valves, guides, or springs? I know Jasper and ATK don't and if NAPA's supplier does I won't be buying one from them.

TOH

Click to expand...

If I had a bud I trusted I would get his opinion... I agree with ya 100 %,,, Its know in the trade ATK does reuse parts that pass and in spec,,, Jasper does offer a (I forgot what they call it) a rebuilt not manufactured engine were they replace worn parts that are not in spec and any machine work needed... Jasper does not s-crew you like ATK they are up front with it.... Unlike a N most of those OHC engines need no head work at 300K :shock:

Experience can not be beat I would accommodate a bud... What ever it took...

This link is the best all around manual for a simple engine rebuild it impressed me.... It covers allot of things you will not find anywhere else....

http://files.leagueathletics.com/Text/Documents/2000/29470.pdf

Got adjustable lifters. Do the flat keepers tell you that the lifters are adjustable? I thought it was set. Not sure. Or the flat keepers tell you that they are rotating? Not sure of that either.

(quoted from post at 07:45:03 12/03/12)
Got adjustable lifters. Do the flat keepers tell you that the lifters are adjustable? I thought it was set. Not sure. Or the flat keepers tell you that they are rotating? Not sure of that either.

Click to expand...

Yer pix is the zaust valve,,, Free rotat'n... Keepers splain it all...

Try not to mix them up they are a beach to set up...

http://ytforums.ytmag.com/viewtopic.php?t=380581&highlight=rotatn

(quoted from post at 23:21:50 12/02/12) Jasper does not s-crew you like ATK they are up front with it....

Click to expand...

Bu "up front" you mean you know your screwed when they tell you the price ;-)

ATK "says" the don't reuse valve train parts. I had one of their engines go belly up within 30 days 0 the other's have all been fine but I haven't purchased onis almost a decade. The one that went bad failed because someone put the wrong mains in it....

I ALWAYS get a price from Jasper and it ALWAYS makes me cringe and go elsewhere. Sort of like re-using vave train parts I suspect - you only get what you pay for and sometime not even that....

"........ failed because someone put the wrong mains in it....

......... like re-using valve train parts ....

Click to expand...

I agree with you , especially on a motor that I paid full price and expect to get 200K miles out of .

On these N's I don't blame used parts but if the person selecting which ones to keep and which ones to replace makes a bad choice then that is the issue .

I would always cringe when buying a used truck from a car lot and the salesman would say "we rebuilt the motor".

I would usually pass and buy the cheaper truck that ran OK with no major repairs done .

Hobo,

I read the link you referenced. There is a bit of confusing talk going on. But straighten me out if I am wrong.

Since I have adjustable rotating valves, it sounds like NO grinding is required. Just properly setting clearance by adjusting the nuts with the special tools.

Do I have it right?

Thanks

(quoted from post at 19:35:12 12/03/12) Hobo,

I read the link you referenced. There is a bit of confusing talk going on. But straighten me out if I am wrong.

Since I have adjustable rotating valves, it sounds like NO grinding is required. Just properly setting clearance by adjusting the nuts with the special tools.

Do I have it right?

Thanks

Click to expand...

Its all in the FO-4 repair manual... Its not that simple to set them up maybe you will get lucky....

It's not about the dirt on the valve, but the condition of the valve face and seat. Seats need to be clean to stay clean, same with valves. concerns on most engines is installed height. If it's not correct, valve tends not to stay seated at higher RPM's, but this engine is not a high RPM engine. Valve springs usually have a valve open and valve closed spec. as well as out of square and free length. Hope this helps. Gerard

I gave my engine buddy the valves that I finish pulling today. He is going to grind the underside of the valves and then he is going to pay me a visit and grind the seats.

I ordered new springs and keepers and the tools to help adjust the valve seats.

I just realized that I forgot to order the rubber seals. There were no seals on the valve guides when I pulled them, but I think they should be there.

Wish me luck. Thanks for teaching me. I will report back once I get it running or if I get stuck. Whichever occurs first.