Help - rebuilt bonnie engine is smoking horribly

[odthing]

I have just about finished restoring my 1961 model T120 bonneville, It started okay, but is smoking horribly from the right cylinder, and the left a bit also. Both plugs are oiling. I thought it was associated with poor oil return, so wwent back to the oil system, checked all okay, even checked the crankcase vent is opening and closing okay. Reseated the oil pump balls (even though it is a new pump). Now happy with the oil return and pressure is fine as well on the indicator, but so much oil is getting into the cylinders, it disels when I switch off!. I am confident it is not coming down from the rockers (new valve guides) and no excessive oiling in the rocker boxes.

I am now wondering about pistons, rings etc which are also new in a rebored cylinder. Any ideas???

[TBS]

Have you checked the ring gaps, and you didn't fit the rings upside down did you?
Also check you fitted the oil lines on the right way round too.

[thunderbird]

had it wet sumped before you started it?as this will make it smoke, remove the sump plate and check the amount of oil that has been retained in the crankcases should only be a small amount

[odthing]

Thanks for the comments so far.

The oil lines are correct, and the oil os flowing back to the tank okay, although I don't think it was at first. I have put a sump plate with drain plug on so have checked, and was a bit surpirsed at how much oil was there after a short period of running. I think the scavenge pipe is now draining all as it feeds bubbles back to the tank after a while. I have checked the airtightness opf the scavenge pipe between the sump and the oil pump manifold face.

As for the pistons, no I did no checks, but fitted them as supplied (allegedly as a set with the cylinders after a rebore). The pistons did go away with the crank for balancing.

I didn't know there wa a right way up for the rings. Tell me more please.

Regards, Will

[thunderbird]

will, piston rings are normally marked which side are top,  the side that should face the top of the cylinder because they are taperd one side this normally the way to fit them to a partly worn cylinder ie one that has a ware lip if they are fitted the wrong way around they may make contact with the lip crushing the ring,as your cylinder has been rebored you shouldnt get that problem,but it would have been worth checking the ring gaps as TBS says,hopefully the excessive smoking is only due to wet sumping

[L.A.B.]

 the side that should face the top of the cylinder because they are taperd one side this normally the way to fit them to a partly worn cylinder ie one that has a ware lip if they are fitted the wrong way around they may make contact with the lip crushing the ring,

That certainly isn't my understanding of why rings have to be fitted the correct way around?

This link has a good description of why tapered rings have to be fitted correctly:
http://courses.washington.edu/engr100/All_Sections/Engine/UofWindsorManual/Piston%20and%20Piston%20Rings.htm

Also there are many variations of top and second compression ring cross-section, and not all are tapered on the outside edge, but still have to be fitted the correct way up.:

http://www.apexpistonrings.com/compressionrings.php#

And it can also be important to fit any one piece oil control ring the correct way around.

[Goldie]

Have you checked that you have not got excessive clearences between the valve stems and the valve guides, because there is only 2 ways oil can get into the cylinder head, via the rings or valve guides.

You have'nt put 2-stroke petrol in by mistake

[odthing]

Thanks for the further replies.

No its not two stroke, although it gives that impression just now.

Given your thoughts on piston rings, and the fact that one cylinder is far far worse that the other, I'll get the head and barrels off and take a look, and also measure ring anf piston clearance carefully this time.

Thanks

Will

[L.A.B.]

What make of pistons/rings are they?

If they are Hepolite/AP/Federal Mogul pistons/rings, then the rings will almost certainly be marked 'TOP', and the bag the rings were packed in would have shown which ring was for the top and which ring was the second.
The oil scraper ring could be a 'three piece' ring or a 'one piece' ring? The one piece ring certainly has to be fitted the correct way around.  

[thunderbird]

didn,t know there were so many different styles of rings LAB   the reason i wrote what i did about the top ring being the right way around was a mate of mine fitted a set of rings to an A10 a few years back but the top ring was fitted the wrong way around and the cylinders were not rebored ie he didnt have the step at the top,that bike smoked like hell untill we stripped it and fitted a new set of stepped top rings with the step at the top

[odthing]

Hi again

The pistons/ rings are Harris, into fresh rebored and honed barrels. I am pretty sure the bottom rings are one piece. If the snow continues I may end up at home this week, so I'll strip it down and take a look.

As previous, the left cylinder is much better but still oily. I am wondering whether this is because the oil not flowing through the crank is released via the pressure release valve into the timing chest and then drains laterally into the crankcases close to the crank, so maybe there is more splashing off the crank on the right side?

Will

[odthing]

Oh, and here is the bike  

[thunderbird]

looks like you have made a nice job of her will [smiley=thumbsup.gif] i had a 61 t120r for many years sadly gone now :(that had comp mag and was running on 11/1 comp pistons it went very well indeed,they are a great bike.it may be a silly question but from your thoughts about the timing side filling with oil i take it when the crank was rebuilt the sludge trap was cleaned?also has the timing cover had the oil seal conversion done or is it still the bush?

[odthing]

Yes the sludge trap was cleaned out - it had decades of gunk in it. And yes I had the oil seal conversion done. I also put a remote cartridge oil filter on. The pressure holds up really well now even at very low revs.

I also put electronic (Boyer Bransden) mag replacement ignition on rather than getting the mag rebuilt, 12V electrics so the lights are great ( with an old style Lucas Mini sealed unit halogen headlight), and a twin leading shoe front brake. The bike is for riding, not for show to rivet counters. Nothing that can't be reversed of course - no new holes or weldling!!

Will

[thunderbird]

sounds like you have done a thorough job hopfully the smoking issue is nothing to serious,i was going to say it looks like you have a twin leader fitted sensible upgrade,i also have the same fitted to my 57tbird it also has pre unit bonnie forks these old bikes will go and its nice to stop also good hear you built the bike to ride my tbird is used alot mixing it with the modern bikes on rideouts and classic runs not into the showing much though. steve