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300 Smoking After Rebuild

14708 Views 35 Replies 12 Participants Last post by  shadetree, 
L
Last summer my 300 was smoking, and low on power and compression. Time for a top end rebuild, pretty standard practice on a 20 year old machine. I was looking for a little more power, so I decided to go with the 317 rebuild with the Rancher piston. I did that combo on my Brothers 300 with good results.

New LA Sleeve, new Honda Piston, new Honda Rings. Sleeve pressed in and honed by local machine shop with a very good reputation that did my Brothers. I put it all back together and the rings kept sticking in the grooves on the piston causing low compression, took me a little while to figure out what was going on. With the compressed rings the piston skirt came into contact with the cylinder wall, removing the fresh cross-hatch. Not enough to feel with your finger, or a pick, but enough to visually notice the vertical lines in the correct lighting.

While the head was off I also lapped the valves, and took a flapper wheel on the Dremmel and cleaned the exhaust and intake port. Removed 20 years worth carbon build up on the valves, ports, and combustion chamber, also knocked down some casting burrs and seams. Nothing major, took my time and just in essence cleaned things up. New valve seals while I was in it.

Put it all back together and it smokes like a freight train, and is blowing oil out of the exhaust port, lots of oil. If you put your hand in front of the exhaust port it comes back splattered in oil, enough oil to drip down the exhaust studs. I figured the rings had to seat or maybe its oil from the rebuild. So I put the exhaust back on and let it idle in the yard for an hour, the smoke never decreased, the oil level dropped 1/2 a quart, and when I took the exhaust off I was able to pour oil out of the muffler.

Since then I have changed the valve seals with a brand new set, and changed the rings with a brand new set. Tested compression, about 165-170 PSI. Took the head off, filled the intake and exhaust port with oil, let each sit for 10-15 min with no draw down, and no oil coming through the valves or valve seals. Filled cylinder with oil, let sit for 30 min with no noticeable draw down.

I'm out of ideas, seems like everything I have done has ruled out the cylinder, rings, or head. But i'm obviously missing something. What could be causing this?
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B
I'd say you either need a different machine shop or you need to look deeper into your motor - crank bearings???

My worry with your machinist would be if he looked for taper and an out of round condition in the cylinder? Did he wait to tailor his bore precisely to your new piston? There are slight production differences.

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk
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L
He had the piston, and I was told he tailored the bore to the piston. Also if the bore was out of round, wouldn't compression be down? I'm pretty confident in this machine shop, they have a very very good reputation with local mechanics and race teams alike, and have done good work for me in the past. That being said I realize they are not infallible, and everyone makes mistakes or misses something from time to time.

Also, how would the crank bearing get oil into the exhaust stream? Could it cause the piston to be out of alignment on the way up, leaving oil on the cylinder wall? What is the best way to check the crank bearing? By hand on the Con Rod?
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Nanook12
Worst thing to do to new rings is idle the engine! You need manifold pressure to break rings in...did you measure the cylinder bore? How about ring gap?
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shadetree
my question is, why in the world did you use rancher parts on a trx300 top end ??. this blows my mind. you should put it back together with all trx300 parts. as for your smoking ?, it's going to be with the piston and rings. just because you have great compression ?, does not mean the oil rings are right ?. you need to pull it all back apart, check the oil rings down in the cylinder, but I would do this with the correct piston and rings, not rancher parts.
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L
Ring gaps are staggered, ring gaps are within tolerances.

As far as rancher parts, its a common 317cc big bore, really no different than ordering a big bore kit from an aftermarket supplier, except i'm using readily available Honda parts, so I can easily get my hands on replacement parts, and i'm using parts of a known quality.

I think the general consensus is that the head is good, but its got to be a ring/piston/cylinder issue. I'm thinking about buying a .25 over piston and rings, and having the cylinder bored by a second machine shop to remove that from the equation.
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mac102004
yeah 317 kit is nothing out of the ordinary, pretty standard setup for a rebuild on a 300.

I'm surprised it's doing this on a full rebuild, especially after changing the rings and valve seals twice, I'm assuming with no visible damage?
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L
No visible damage, as I said when the rings stuck when I first put it together the piston skirt rubbed the cylinder wall, just enough to remove the cross hatch, and add a vertical line. But you cant feel it with your finger, fingernail, or by running a pick across the cylinder wall. I'm very surprised as well. When I did my brothers 2 years ago it went together fine, fired right up, with no problems which is why I went that route again. I haven't done anything different this go around that I know of. I'm thinking a do-over with a .25 over piston and rings unless anyone has another idea. I just hate wasting $150ish on a new piston, rings, gasket, and labor if that's not the issue.
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mac102004
I got nothin man, sorry. Have you asked on the Honda 300 club facebook page? There are some smart guys there that know more about the 300's than I do.
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L
I have, got recommendations anywhere from a cracked head, bad valve seals, "time for a rebuild", and it'll go away on its on. So no real help.
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dr. feelgood
Nothing more disheartening than having issues after a rebuild. I had a Suzuki Vinson last year that was smoking bad. I put new rings in it (nikasil cylinder so it still looked new) and fired it up and it still smoked. I went out and rode it hard for a bit and the smoking cleared up.

Rob
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shadetree
dr. feelgood said:
Nothing more disheartening than having issues after a rebuild. I had a Suzuki Vinson last year that was smoking bad. I put new rings in it (nikasil cylinder so it still looked new) and fired it up and it still smoked. I went out and rode it hard for a bit and the smoking cleared up.

Rob
Click to expand...
welllllllllllllll...lol, first..yes..chit happens !. but if a person takes their time, uses the correct parts ( or just makes sure parts will work ? ), then you worry about if your work was done right ?. I've been down the same road as the OP many times !, it sucks to rebuild something, and it not run right ?, or something else pops up, that you had no clue there was a problem, or what caused it ?, until you discover it !..lol. had this problem on an old trx350 rancher many moons ago, damn thing ate my lunch and some !..lol. little did I know, that the valve seat could work it's way out of the head once warm/hot ?. I replaced almost everything new with oem, and it still made a rattle when warm/hot ?..that's when I looked into this matter deeper, and found out Honda had a defective head on some of their trx350 rancher heads !..lol.
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Manny
To take all guesses out of the situation pull it apart and measure your piston to bore clearance, measure to see if the bore is out of round.

btw, you wont get a good gauge at whether or not your valves are leaking with oil, your best bet is using carb clean, brake clean, or even gas, dump it in the intake and exhaust ports and see if it seeps through.

My bet is the bore is out of round. even though its new, it should not consume that heavily.
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shadetree
Manny said:
To take all guesses out of the situation pull it apart and measure your piston to bore clearance, measure to see if the bore is out of round.

btw, you wont get a good gauge at whether or not your valves are leaking with oil, your best bet is using carb clean, brake clean, or even gas, dump it in the intake and exhaust ports and see if it seeps through.

My bet is the bore is out of round. even though its new, it should not consume that heavily.
Click to expand...
I agree, something is not right with the bore/piston/rings.
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Manny
btw, was this machine sunk? if so, you could have grit in the bottom end causing the premature failure.
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J
shadetree said:
dr. feelgood said:
Nothing more disheartening than having issues after a rebuild. I had a Suzuki Vinson last year that was smoking bad. I put new rings in it (nikasil cylinder so it still looked new) and fired it up and it still smoked. I went out and rode it hard for a bit and the smoking cleared up.

Rob
Click to expand...
welllllllllllllll...lol, first..yes..chit happens !. but if a person takes their time, uses the correct parts ( or just makes sure parts will work ? ), then you worry about if your work was done right ?. I've been down the same road as the OP many times !, it sucks to rebuild something, and it not run right ?, or something else pops up, that you had no clue there was a problem, or what caused it ?, until you discover it !..lol. had this problem on an old trx350 rancher many moons ago, damn thing ate my lunch and some !..lol. little did I know, that the valve seat could work it's way out of the head once warm/hot ?. I replaced almost everything new with oem, and it still made a rattle when warm/hot ?..that's when I looked into this matter deeper, and found out Honda had a defective head on some of their trx350 rancher heads !..lol.
Click to expand...
Interesting and good to know.

The Rancher I've been rebuilding for my neighbor runs good now. It quit burping oil into the airbox (rings must have seated), carb quit leaking with a new float needle, and the disc brakes from a 420 Rancher stop it great.

It rattles like hell though, and I adjusted the valves before I ever tried to crank it.

He got a parts bike with this one, so maybe I'll swap the heads and see if it helps.
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wheeler
After reading this thread, the first things that jump into my mind... oil rings, compression rings installed correct, & the cylinder matching piston. Triple check the valve seals as well. They would have to be way off for it to smoke all the time though.
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Manny
Jeep, make sure the cam followers are in good shape and one of the push rods aren't bent too. thatll make er chirp.
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shadetree
Jeepwm69 said:
shadetree said:
dr. feelgood said:
Nothing more disheartening than having issues after a rebuild. I had a Suzuki Vinson last year that was smoking bad. I put new rings in it (nikasil cylinder so it still looked new) and fired it up and it still smoked. I went out and rode it hard for a bit and the smoking cleared up.

Rob
Click to expand...
welllllllllllllll...lol, first..yes..chit happens !. but if a person takes their time, uses the correct parts ( or just makes sure parts will work ? ), then you worry about if your work was done right ?. I've been down the same road as the OP many times !, it sucks to rebuild something, and it not run right ?, or something else pops up, that you had no clue there was a problem, or what caused it ?, until you discover it !..lol. had this problem on an old trx350 rancher many moons ago, damn thing ate my lunch and some !..lol. little did I know, that the valve seat could work it's way out of the head once warm/hot ?. I replaced almost everything new with oem, and it still made a rattle when warm/hot ?..that's when I looked into this matter deeper, and found out Honda had a defective head on some of their trx350 rancher heads !..lol.
Click to expand...
Interesting and good to know.

The Rancher I've been rebuilding for my neighbor runs good now. It quit burping oil into the airbox (rings must have seated), carb quit leaking with a new float needle, and the disc brakes from a 420 Rancher stop it great.

It rattles like hell though, and I adjusted the valves before I ever tried to crank it.

He got a parts bike with this one, so maybe I'll swap the heads and see if it helps.
Click to expand...
if the cam chain is good ?, and valves are set right ?, i'll bank on the valve seat coming out when it's warmed up !..lol. I know this for a fact !. I replaced cam, cam chain, valves were good as far as valve clearance , and it started up great, but once it got warmed up ?, i'd hear what sounded like a bad cam ?, bad cam chain ?, replaced all of that with new oem, still did the same thing. well, after it did it again, I shut it down, pulled the head, and after closely looking at the valve seat under the springs ?, I could see them sticking up ?..asked my bud at my dealership, he says '' oh yeah..those ranchers had a defective head on some of them '' ..now I learned something..lol.
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L
Manny said:
To take all guesses out of the situation pull it apart and measure your piston to bore clearance, measure to see if the bore is out of round.

btw, you wont get a good gauge at whether or not your valves are leaking with oil, your best bet is using carb clean, brake clean, or even gas, dump it in the intake and exhaust ports and see if it seeps through.

My bet is the bore is out of round. even though its new, it should not consume that heavily.
Click to expand...

Will try with regular unleaded tonight. But i'm now thinking the cylinder as well. If I had to guess something is up with the cylinder, the compression rings have enough pressure to seal up or meet the imperfection, but the oil ring does not and it is leaving a film of oil on the cylinder wall. That would explain the good compression, and no draw down on the oil I put in the cylinder last night, but still having some blow by during the compression stroke. On that note though, wouldn't the compression rings be tight enough against the cylinder to scrape the oil off?
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