Topic: Rebuilt Top-end Burning Huge Amounts of Oil

[mgilvary]

I have a 1975 CB550 that I've just bored out to 605cc, using a NOS overbore kit (bigger pistons, bored out sleeves, oversize head gasket, etc.). I also installed all new valves, guides and springs, with a machine shop performing the boring and honing of the cylinder and all valve machine work, including installing the guides.

This weekend, when I finally got it all back together and started it up (after more than 2 years disassembled!), it started spitting out massive quantities of whitish smoke -- pretty obviously well-burned oil. Since I had poured a little oil over each piston prior to assembly, I figured it would burn off after a few minutes. But it did not. In fact, it filled my neighborhood with noxious smoke.

I coasted it down the hill to a wider, less populated street and started it back up. Let it run for 20 minutes. Still churned out the same amount of smoke with no signs of letting up. And it appears to be coming from all four cylinders more or less equally. 

When I got it back home, I checked the oil. Dipstick was bone dry, though I had refilled the crankcase after reassembly.

So, I ran a compression check. All four cylinders are strong, about 160 psi.

I've done a lot of work on this bike over the last 5 years, but am still really a noob, so I'm having trouble figuring out what went wrong. Here's my best guess.

When reassembling the engine, I had eight extra o-rings from my gasket set. I could not figure out where they belonged, so I studied the parts list and found eight o-rings that appear to go between the valve guides and the head. Since the guides were already installed -- I had no means of pulling them and reinstalling to check -- I just assumed that the machine shop installed their own o-rings.

Could that be the cause of this oil leak into the cylinders?

I'm guessing the oil has to be coming in from above and not past the rings, since compression is strong and the volume of burning oil is tremendous -- almost a quart in less than 30 minutes of running. I know there are oil seals around each valve stem -- I installed those myself. But if those o-rings are missing between the guides and the head, could a large volume of oil be draining down into the chambers that way? I'm pretty sure I did not miss any other o-rings or gaskets (I had a much more skilled friend checking my work during the reassemble).

Is there any way to verify the source of the oil leak without pulling the head?

Any input is greatly appreciated. It took me two years to find the money and time to complete this project. I'm at a loss here.

[turboguzzi]

even without valve stem seals, there's no way that the engine will use as much oil. Run a full season without them and it never smoked badly at all. Just cant believe that all that oil is all going into the engine through the guides, no way.

Compression rings might do the job but not the oil, so the fact that you have 160 reading doesnt mean oil isnt getting past them, most likely it is.

Did you have a look at the plugs removed?  They must be pretty soaked, but was there one that was more oil soaked than others? You might have broken a ring in that one.

Last, in an aftermarket kit I would be suspicious of the rings quality. The oil ones in the last set I used lost all tension after three races and the bike was indeed smoking quite a bit.

my 0.02

[ColinMc]

Also, did you top off the oil AFTER it first ran for even a few minutes. If you did a complete tear down it'll take some oil to recoat everything inside the motor...

Did you put the rings on correctly? With the gaps on the various rings spaced appropriately?

[Toxic]

Also, did you top off the oil AFTER it first ran for even a few minutes. If you did a complete tear down it'll take some oil to recoat everything inside the motor...

Did you put the rings on correctly? With the gaps on the various rings spaced appropriately?

Pretty sure this is where your missing quart is.  After your first start up you would have to re-fill
the tank.

I remember a complete rebuild I did and it took a good while to burn off all the assembly lube I used.  I over did it on the lube.  It wasn't still burning off after 30 mins though.

sorry but I don't see you solving the problem without ... well you know.

[mgilvary]

Also, did you top off the oil AFTER it first ran for even a few minutes. If you did a complete tear down it'll take some oil to recoat everything inside the motor...

Good point. No, I only filled it prior to starting up. But still, there's no question this thing is burning a lot of oil. Here's a pic:

Did you put the rings on correctly? With the gaps on the various rings spaced appropriately?

Yes, I was very careful about that.

Also, turboguzzi:

To clarify, I'm not talking about missing valve stem seals. I'm talking about missing 10 x 1.6 o-rings that sit between the guides and the head. They would be right at the bottom of the little well in the head where the valves enter and, I presume, a lot of oil would collect.

And I forgot to mention the plugs -- yes, they are soaked with oil. Pretty equally.

[Raul CB750K1]

Wow, that bike seems to be a two-stroker....

[ColinMc]

Does it smell like burning oil? White smoke can be moisture burning off...is it a new exhaust as well? A lot of them have a coating on the inside that takes a while to burn off as well...I'd say fill er up, make sure you are getting oil pressure, and take it for a rip to really get things up to proper temperature...but then again that could just make things worse...lol

[mgilvary]

It's definitely oil. And the exhaust is not new.

I took it for a quick spin up and down the road. Made no difference. Still smokes like crazy.

[turboguzzi]

I see what you mean now but still, older bikes and cars didnt used to have o rings at the guides and yet never burned oil like that. the fit of the guides is pretty tight, hard to imagine such a massive oil leak through the non existing gap ( unless your shop did a VERY sloppy job there).

you could in theory lift the rocker cover, shut off somehow the draining holes of the valve spring cavities (next to the cam chain), pour some light oil into them and leave it over night. if the oil disappears then its leaking down the guides.... just an idea.

i still think its rings related but you could give it a try

[MRieck]

What brand piston kit is in there?

[bistromath]

mrieck's got it. if it's the kit with the single-piece oil rings, they're notorious for burning oil. still, that's a little more than i'd expect.

[Zaipai]

mrieck's got it. if it's the kit with the single-piece oil rings, they're notorious for burning oil. still, that's a little more than i'd expect.

Yea I would bet that is the problem. To burn that kinda oil and have that much compression I don't think its leaking oil via the valves..

[HondaMan]

A couple of questions and comments for you, based on bikes I've had to "fix" after some other shop got done with it... 

1. What was the piston-to-bore clearance after the machine shop set it up? I have very recently seen 2 bikes where the shop made the clearances excessive (one was .002", which will very quickly become 0.003", and the other was a whopping .004": neither engine works well, both burn oil, lots).
2. If oil is getting past the rings, it will show excessively high compression in situations like this. the oil is making the compression appear artificailly higher.
3. Could the rings have gotten cracked during installation? On the 550, it's fairly easy to check this, although it will cost you another top-end gasket set to find out. You can remove the head and look into the bores: if there are vertical lines cut on the cylinder walls, the ring(s) is/are cracked. If caught early, and the piston-to-cylinder clearances are like they should be (about 0.001" or so), you can often just hone these out and install new rings to fix it up.
4. About those little O-rings: maybe try to find the machinist who worked on the head and ask if he/she remembers if the O-rings were replaced when the guides were removed? It would seem irresponsible (to me) for someone to pull out old guides, see the O-ring, then install new guides without the seal. (But sadly, I have recently seen much worse...).

I get closer to 'building' a machine shop just for SOHC4 bikes every time I hear this stuff....I just need to figure out a good shipping method that doesn't ruin the cost of it for everyone.

[mgilvary]

What brand piston kit is in there?

No idea about the brand. It was an NOS kit I bought off eBay about 3 years ago. The box says "CB-605cc Kit - Made in Japan."

I think the oil rings were one-piece, if that is what you're getting at. 

HondaMan:

I don't have the specs from the machine shop. I didn't deal with them directly. I had a mechanic acquaintance send it to his machine guy. I'll have to get him to put me in touch with them to find out measurements and about the o-rings.

[bucky katt]

hm, i ran 1 piece rings in my k4 and had around 10k miles on them with bery very little oil use as in less than 1/4th a quart between oil changes they were supposedly oem rings and pistons but i dont know for sure

[754]

Valve guides should be a press fit.

 During removal, regardless of how you clean it, you usually get scratch lines in the guide bores. One way to eliminate this, is to drill thru the top of the guide, snap off the upper end, then drive them INTO the port.. but not many take the time to do this.. I have done it sometimes, BMW actually recommends this method.

 Back to the guide and oring or on some bike heads washers... this is to seal them, if they got damaged.

 But they would not burn that much oil..

 I am thinking, it is excessive bore clearance, and or ring fit..
 do you have spare barrels, or did the kit have sleeves?

[bucky katt]

are you getting any knocking noises? perhaps put a mechanics stethoscope onto the cylinder bloxk as far in as you can between the fins.

[mgilvary]

I am thinking, it is excessive bore clearance, and or ring fit..
 do you have spare barrels, or did the kit have sleeves?

Kit had sleeves, but the shop did not use them. They chose to leave the originals in place and bore them out. So, I do still have spare sleeves from the kit, worse comes to worse.

[mgilvary]

are you getting any knocking noises?

The engine sounds reasonably good, considering that the carbs need syncing and the ignition timing hasn't been dialed in. I tried to do the timing, but got smoked out pretty quick.

[ColinMc]

I am thinking, it is excessive bore clearance, and or ring fit..
 do you have spare barrels, or did the kit have sleeves?

Kit had sleeves, but the shop did not use them. They chose to leave the originals in place and bore them out. So, I do still have spare sleeves from the kit, worse comes to worse.

Was this a good idea?! I have no idea just throwing more options out there.

Now you said it's smoking out of both exhaust rights? Have you checked the plugs yet?

[HondaMan]

hm, i ran 1 piece rings in my k4 and had around 10k miles on them with bery very little oil use as in less than 1/4th a quart between oil changes they were supposedly oem rings and pistons but i dont know for sure

In situations where you are just re-ringing an engine, and are using one-piece oil rings, you must thoroughly hone the bores to make the process successful long-term. Otherwise, use the 3-piece rings. They are more forgiving of the marginal hone job. It seems that too often, the non-experienced home mechanic just does not know for sure what the honing job should look like, so it ends up not being quite enough. 

The 3-piece rings are a pain to install, though, IMO.

[HondaMan]

 During removal, regardless of how you clean it, you usually get scratch lines in the guide bores. One way to eliminate this, is to drill thru the top of the guide, snap off the upper end, then drive them INTO the port.. but not many take the time to do this.. I have done it sometimes, BMW actually recommends this method.

What a great idea! Thanks! 

[MRieck]

hm, i ran 1 piece rings in my k4 and had around 10k miles on them with bery very little oil use as in less than 1/4th a quart between oil changes they were supposedly oem rings and pistons but i dont know for sure

In situations where you are just re-ringing an engine, and are using one-piece oil rings, you must thoroughly hone the bores to make the process successful long-term. Otherwise, use the 3-piece rings. They are more forgiving of the marginal hone job. It seems that too often, the non-experienced home mechanic just does not know for sure what the honing job should look like, so it ends up not being quite enough. 

The 3-piece rings are a pain to install, though, IMO.

Really Mark.   I have always found them to be the easy part because they are low tension.

[754]

Nearly every guide, will have a relief under the shoulder, or it has a snap ring. Evo motors may be an exception as they use a driver with a set counterbore depth to place the guide to correct depth in head. Anyway I think guides are generally ground (after mounting on a precision mandrel) to size after rough turning on a lathe, so with the relief/groove under the head, you dont hit the shoulder, when grinding to finish.

 So unless the guide is very hard (some did use hard steel guides at times), it can be drilled.  If you rig up a pin to go in the guide it helps hold the head. You have to be careful here dropping a head will ruin your profit! Drilling about a 32nd undersize(or a bit smaller), you drill to the groove area, .. sometimes the guide end will come off at that point, or it may need a slight tap. Then drive the guide into the port. Of course if guide is longer than the port, that would be a problem.

 The ones I have done like that look like a burnished hole, more like a master cylinder bore! The cool part is you can keep using standard guides.  Most guide holes, even after  firs tbead blasting, got lines or grooves in them,  Some folks recommend digging around the guide to get the last carbon out before removal, I think this can make it worse as next time, its even harder to clean it out.

....................................................................

Back to the oil burner, I think the sleeves may be very thin, and maybe too much bore clearance..

 A lot of times the person doing the work, uses what they think clearance should be and its often clearance used on a 3.5 inch car piston..

[Gamma]

I'm no expert, but could it be the second scraper rings upsidown?

I found 3 piece oil rings easy if you put the expander in first then the top and bottom rails.