rusty cylinders

Hi fellow bikers, My question is ...

If my cylinders (2 out of the 4) on my 78 KZ650 had a tiny bit of rust on them that was deeper than the rest of the bore, say about .oo1 of an inch deeper would that cause my bike to smoke like a freight train? Keep in mind that I did a valve job (lapped the valves and put new valve stem seals)and it seemed to be as tight as a drum. I also put new rings on it. heres a tip, it smoked with the old rings and it smoked the same after the new rings. I honed the cylinder between ring jobs and there was a bit of rust that the hone couldn't get out, but I put it back together any way :pinch:. So is that why its smoking? I'm voting yes! Any thoughts?

Thanks, Matt

Sounds likely. It might be smoking because the new rings have not seated yet. You didn't bore it which means the bores are not perfectly round and the new rings will have to cut the bores to their liking (if they can) before you get a tight seal.

I thought about that but I've rebuilt 5 engines (3 motor cycles) and none of them ever smoked after rebuild, new bore or old.

Matt-

You don't give the location of the rust pits relative to ring travel so it's difficult to say for sure.

If these pits are in the center of the cylinder vertically, so that the rings travel from above the pits to below the pits, then it's certainly possible (and likely) that the pits are trapping oil then exposing it to combustion heat causing it to smoke.

I remember one MGB engine that I built and it smoked like crazy. Turned out to be a hole in the vacumn operated pcv valve diaphragm. It was sucking oil straight from the crankcase.

a quick check would be a compression check, also did you check the spark may be a weak.

yes the rust does travel vertically through out the path of the rings. I think my spark is fine, but I have no proof of that, The PCV is that hole on the rear top part of the engine case, right? I have tried plugging that hole and I also let it breath (opened it) it smoked either way?

the good news is that I got a set of jugs from ebay yesterday so I think I will bore it out (because I have .5mm over pistons)and then I'll be able to start fresh. Any objections?

Thank, Matt-

If these pits are in the center of the cylinder vertically, so that the rings travel from above the pits to below the pits, then it's certainly possible (and likely) that the pits are trapping oil then exposing it to combustion heat causing it to smoke.

Thank you for that, steell. It's 4 stroke stuff like this that I never think about. 2 stroke stuff I live and breathe, but 4 stroke stuff....well, let's say I just need more experience on overhauls....and hopefully it won't be MY stuff needing the overhaul.:laugh: :laugh:

Hey, UPDATE! I got my replacement jugs from "ebay" so now I have to get them bored over .5 mm (20thou). How much should I expect to pay for a bore job. I got a price off about $200 from my local machine shop but they don't usually do motorcycle jugs. Any advice?

Matt-

zeiss150 wrote:

Hey, UPDATE! I got my replacement jugs from "ebay" so now I have to get them bored over .5 mm (20thou). How much should I expect to pay for a bore job. I got a price off about $200 from my local machine shop but they don't usually do motorcycle jugs. Any advice?

Matt-

I would send them to someone who knows bike motors. I'm sure the local guys can do it but I like the piece of mind getting machine work done by someone I know is qualified and has experience.

zeiss150 wrote:

Hey, UPDATE! I got my replacement jugs from "ebay" so now I have to get them bored over .5 mm (20thou). How much should I expect to pay for a bore job. I got a price off about $200 from my local machine shop but they don't usually do motorcycle jugs. Any advice?

Matt-

I think it was $75 per hole at the machine shop here.

donthekawguy wrote:

zeiss150 wrote:

Hey, UPDATE! I got my replacement jugs from "ebay" so now I have to get them bored over .5 mm (20thou). How much should I expect to pay for a bore job. I got a price off about $200 from my local machine shop but they don't usually do motorcycle jugs. Any advice?

Matt-

I would send them to someone who knows bike motors. I'm sure the local guys can do it but I like the piece of mind getting machine work done by someone I know is qualified and has experience.

I went to the dealer where I got my bike and started shooting the bull with a couple of their mechanics and found out the name of the machine shop they send their heads and cylinders out to. best in the area, you might get similar results.