Jump to content
Rich16

Worth Replacing Piston Rings p220g?

Recommended Posts

Rich16

Hi All,

I have a '91 520h with around 550hrs - starts and runs great but does smoke on start-up and when revving - definitely oil - but not noticeable when mowing.

I also found another p220g exact replacement with similar hours that does about the same thing - right now a 'play' engine with some oil smoking on start and when revving.

Cleat has been great help getting my replacement engine running.

I know I need to de-carb the heads - would it be worth replacing the piston rings on both engines or better to just leave well enough alone?

I can do the work - but I also know that when things aren't broken..... the rings are still available and inexpensive - any thoughts?

I don't want to get into anything more involved but I don't know what 'normal' is for these.

Opinions welcome!

 

Share this post


Link to post
Share on other sites
 
clueless

Don't know much about Onans. but if both are smoking with less than 600hr, there are other problems than rings.

  • Like 2

Share this post


Link to post
Share on other sites
 
Rich16

That's my thinking also - though I've got a 416-8 single cylinder Kohler I bought new (and has been maintained) that behaves similar - maybe doesn't smoke quite as much but definitely does on cold startups.

I presume until any engine like these warms up and the rings expand there's going to be some? Also seems worse in colder weather.

They both run fine after warming up - which is why I'm debating the wisdom of doing anything. I do have a 'spare' engine which would be easy to play with - I dunno.

Why others more familiar with the p220g Onan (I'm not until I bought the 520h this summer) would be helpful in opining?

I'm old enuf to know if it ain't broke don't fix - but I want to extend whatever life I can get out of these and parts getting harder to find.

  • Like 1

Share this post


Link to post
Share on other sites
 
ericj

The bigger question would be does it use oil, if you have to add oil before every use then maybe it's time to look into freshening the motor up. If you don't have to add oil then I would just run it, in fact I have a 516-H that I mow with I only have to add oil once or twice a mowing season, so to me it's not worth the expense to rebuild

 

 

 

 

 

eric j

  • Like 2

Share this post


Link to post
Share on other sites
 
lynnmor

550 hours is nothing for an Onan, IF, and I say IF it was properly maintained.  All my P220G engines will give a puff of smoke when started cold and they do use a small amount of oil.  Since you want to decarbon, check the bores and measure wear, it also would be a good time to check the valve guides, replace the intake valve seals and adjust the valves.

  • Like 2

Share this post


Link to post
Share on other sites
 
Rich16

Appreciate the thoughts. Both engines start right up and run fine - I haven't notice the 520h engine oil dropping on the stick and don't think it's burning that much.

Unfortunately I don't know how either was maintained - I do know neither has spit any valve seats and both engines idle smoothly and rev nicely.

Thanks Lynnmor for the 'normal' behavior of the p220g engines - what I really needed to know.

I figure after all, they're pushing 40 years old and are still workhorses! Even auto engines do this when they haven't been run very much.

Engine maintenance issues aside, probably the most bothersome thing is it smokes up my garage (and is a disagreeable smell) for 15-20 minutes - so much so that I usually  hand push it out and then start it up.

I know back in the 'old days' I used to occasionally change the rings on lawnmower engines when they'd lose compression and it wasn't that big a deal.

Would it be correct to say that since the heads will be off anyway that you can just drain oil, drop the pan, flip it over, disconnect the rods from crank, shove the pistons out, and replace the rings without getting into anything else? Could replace the intake valve seats at the same time.

I'm retired and have the time - but it'll still be a big job - but kinda fun :-)

Share this post


Link to post
Share on other sites
 
pacer
24 minutes ago, Rich16 said:

correct to say that since the heads will be off anyway that you can just drain oil, drop the pan, flip it over, disconnect the rods from crank, shove the pistons out, and replace the rings without getting into anything else?

 

I just did this very thing (only on a B43 Onan) The tractor had forty+ years of chaff, dirt, oil, etc build-up and knowing the Onan seems to ESPECIALLY like lots of cool air, I pulled the engine to get to all the fins, etc cleaned-- dern good thing too! It was badly clogged! So, the engine is sitting on the bench 'naked' so to speak and not having any history on the tractor/engine, I figure why not go ahead and open er up and do an inspection. Well, that part was good - standard bore and virtually no visible wear. With the import rings/pistons etc so reasonable I went ahead and ordered them, (about a 100$) since not knowing anything about the engine, and I went ahead and pulled the valves and inspected them and gave them a slight dressing. I only have an hour or so on it since then but --- so far so good!

  • Like 1

Share this post


Link to post
Share on other sites
 
Rich16

Thanx Pacer! Great info and please keep me informed of your progress and how much difference it makes.

I'm thinking about buying a couple sets of rings just to have - the engines I have are standard bore and I doubt my area is capable of boring them larger anyway.

Get parts while you can!

Love your user name - I had a '75 AMC Pacer stick - the first year - I really loved (despite the negative comments I'd get).

Share this post


Link to post
Share on other sites
 
lynnmor

Your description of the startup smoke sounds excessive, but I can't see it from here.  I always am ready to drive out of a building as quickly as possible after a cold start.

 

You said that the valve seats are OK, but you can't tell by compression readings until they are real bad.  Ask me how I know.  If the valve seats are tight, I wouldn't disturb them.  I freshen up the seats and valves whenever they are accessible.

 

Replacing rings is probably more involved then your simple description, download the Onan manual on this site.

 

It is a good idea to remove the tins and thoroughly clean the fins.  While the tins are off, consider replacing the oil filter mount gasket.  Be sure that you have the rubber around the oil filter to prevent loss of cooling air.

 

It does sound like you want to make it as good as possible, so replace fuel and vacuum lines, check and repair any intake manifold leaks, glass bead the exhaust and apply rustoleum high temperature paint.

 

As you progress, ask questions here.  Good luck.

  • Like 1

Share this post


Link to post
Share on other sites
 
Rich16

Thanks Lynnmor - I'm sure the valve seats need cleaning & hope they're otherwise OK. I've heard the sound (youtube I think) they make when disaster strikes and the seat's been expelled from the rear cylinder due to overheating and fortunately mine both sound fine - but point taken - you don't know until you know.

 

Since I already have a spare engine it's a great playtoy - easy to remove tin and I've already removed the orig shot muffler and there's minimal rust on the replacement i'm removing with evapo-rust - expensive but that stuff's amazing. I waited long enough and a near-mint muffler showed up on eBay with hardly any rust at all!

 

Since the muffler's off - the intake's easy to remove now - figured it's just a matter of removing the heads and the oil pan and flipping it sideways or upside down?

 

There's a guy on youtube who did an excellent series of a complete b43g teardown in 11 segments - really good and more than I ever plan on tackling.

 

I have RustOleum heat resistant paint but it's supposed to 'cure' at fairly high temp - have you ever started one, let it run until hot, and painted it while on the engine? Bad idea? Or is it better to paint, cure at room temp, and hi-heat cure while letting the engine run?

 

Thanks for all the other suggestions - what is glass beading the exhaust? Like sandblasting or something else? The replacement muffler is in 95% new condition and I'm lucky to have found it.

 

Many thanks for all the help.

Share this post


Link to post
Share on other sites
 
lynnmor

It is amazing how well those engines can run with loose valve seats, the seat can seal on the bottom till they get real bad.

 

The manual is here: manual  The piston removal should be fairly easy since you will have the tins and heads off anyway.  Doing the deglazing with the crankshaft in place will take some caution so that it is not hit and cleanup will take some effort.

 

Glass beading is the same as sandblasting, but not so aggressive, you don't want to remove more of that thin metal than necessary.

 

The high temperature paint will cure the first time the engine is run till it gets hot.  You want to do this well away from the house.

  • Like 1

Share this post


Link to post
Share on other sites
 
Rich16

Thanks again Lynnmor! Very helpful.

 

I found something when taking off the muffler - don't know if this has been reported on the site or not but it certainly could be contributing to smoking - and might be a reason to take off the muffler every few hundred hours or so.

 

It didn't want to come off easily - it would wiggle and I could pull the front partly out but the rear was stubborn... it finally pulled out after more aggressive wiggling (and me looking for some other screw needing loosening I'd missed - maybe the one in my head :-)

 

To my surprise a roundish black semi-hard ball of caked oil (about 3/4-1") fell out at the front cylinder where the muffler pipe flange joins the engine - which would be right above the exhaust valve stem I presume. Fluke? Normal? Dunno.

 

But I'm certain that would be a nidus for plugging up the exhaust for that cylinder and maybe smoking every time it got super-hot when the engine was running?

 

I'm glad now it had the bad muffler - otherwise that would have been a problem waiting to screw up the exhaust valve or something else? Easy enough to yank off and just have to replace the gaskets - might check my 520h engine also. Ever run across anything like this?

Share this post


Link to post
Share on other sites
 
lynnmor

To make a ball like that the engine is consuming too much oil.  I have never seem more than just caking in the ports.  Follow thru with the ring replacement and look for valve guides with too much clearance. 

 

When installing the muffler, first run a bottoming tap in each hole to make the threads as deep as possible, then you might be able to use bolts that are a bit longer.  The reason for this is that those holes are very easy to strip, especially when using anti-seize.  Coat the muffler pipes with anti-seize where they go in the block.

  • Like 1

Share this post


Link to post
Share on other sites
 
Rich16

Many thanks for the great tips - probably won't get to it until the spring but I'll post what I find when I take it apart.

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...