smoking oil but why?

[TopDogDave]

OK so take a working XR600R.
Not smoking (note this bit) but had a hard life so time to invest in a few farkles.

Do these things

1. aluminium weld extra large fins to head - I just like the look not for serious cooling (this task was done first)
2.rebore and fit new piston/rings-now is 628cc (engineering co did this not me)
3.fit stage 1 cam and remove decompressor as new cam does not support it
4. fit new valves and guides and oil seals (lurking under the guides) (engineering co did this not me)
5. clean out and re-pack white bros exhaust


Compression = good.
Fires up OK.

Smokes on startup then extremely worse after a few mins warm up. Unrideable around town.
Plug is black as you would expect. oil smoke not rich fuel smoke.

So...where's the oil getting in?

Head and barrel/piston removed and re-checked by engineering co who reckon measures are in spec.
Re-assembled = still smoking.

I have no idea - do you!?!?!?

the only small voice in my tiny head says "did you get a minute crack in the combustion chamber area when they welded the fins...so how to eliminate this possibility?"

Dave

[pommie john]

Rings installed wrong? Upside down?

Take off the carb and shine a torch down the inlet port. Does it look oily down there near the valve? If so it's likely to be the inlet guides or the seals on them.

[bk brkr baker]

Did you replace the valve seals after the welding ?

[markjenn]

Originally Posted by TopDogDave

1. aluminium weld extra large fins to head - I just like the look not for serious cooling (this task was done first)

I'm curious how this was done. Pictures? I would think this could cause some serious barrel/head distortion.

- Mark

[England-Kev]

Originally Posted by pommie john

Rings installed wrong? Upside down?.

This was my first thought too, also is the ring gap too big?

[JeffS77]

ring gap, rings not properly installed or something wrong with the valve guides/seals. one of the three would be my guess

[corndog67]

Originally Posted by markjenn

I'm curious how this was done. Pictures? I would think this could cause some serious barrel/head distortion.

- Mark

Common XR600/XR650 mod, mine had the same thing. They usually dust off the head gasket face on a lathe or mill to make it flat again.

You've got a couple options. Rings, or valve guides/seals. Cylinder wall finish correct for the ring material? Chrome rings, real smooth, cast iron rings, not so smooth. Check with the manufacturer of the piston kit.

[concours]

Tell us about the big bore kit... Factory Honda parts, in oversize? Or aftermarket piston and rings? Could be bad bore size, bad oil rings, poor valve guide fit into the head, guide to stem, seals incorrect, out of place. Do you have precision measuring tools? Start with the bore. The engineering company should solve this problem for you.

[TopDogDave]

Thanks for all the replies.

There's no evidence of oil in the inlet/valve area.
The oil seals under the valve guides were replaced after the welding not before so they can't have been damaged by it.
The head surface wasn't distorted by the welding so did not need to be skimmed.
The rings are in the right way up and gaps are good.

At least no-one has come up with anything new so it MUST be one of the above and I've been too slack to notice!

For those interested in the big fins head.

I first made some templates out of art plastic and scuplted them to fit each fin. then took the templates to the fab shope where they used them to cut aluminium ones and welded it all up.

I have a proper oil cooler for the intense Aussie desert heat.

Pics:
making templates




oil cooler



showing std head (left) and extended fins after welding (right)




in situ






look at the black oil crap coming out of the exhaust

[photomd]

I'd want to check those exhaust guides. Pull your valve cover and poor oil on the head so the exhaust guide has oil sitting on it, then look in the exhaust port. Any oil running down the valve? Any sign of exhaust blow by around the valves? If those are OK, I'd check the breather system careful and then pull the cylinder and check the piston to cylinder clearance as well as double check the rings.

[England-Kev]

Stick your spare head back on the bike, and give it a run, if you are still getting the same problem it is cylinder or rings, if you don't get the same problem, it is something in the head.

Who did the rebore, I would check to see if it is correct, and not oval, maybe you have oil blowing past the rings?

[cam14]

An easier way to diagnose your problem is to perform a leak-down test. Set at TDC (Top Dead Center) apply compressed air through the spark plug hole via the leak-down tester. If you can hear air excaping through the oil tank, then rings never set correctly, if air is coming out the rocker cover then valve guides are bad.

On related topic, if smokes more on acceleration, then likely rings, if smokes more on compression braking (deceleration) then likely valve guides.

From the description you have provided, I would guess rings.

BTW, I have a big fin head on my XL600, so far so good.

[anotherguy]

After a little electronic manipulation the photo indicates the oil is coming past worn valve guides or bad seals. See the clean area by the valve head where it seals and the valve stem just as it enters the guide? Did you replace the valve guides when rebuilding the head? If you blow the photo up and look at the guide where it enters the head there appears to be some carbon beginning to build up as well as some unburnt oil which tells me it's getting by the guide head interface too.

[creaky]

My experience with XRs from 200s to 650s. Smoke on startup that clears up after a few minutes warmup is valve guides/seals, might see some smoke after deceleration when the throttle is opened. Smoke that begins lightly on startup and gets worse as the engine warms is oil getting past the piston/rings due to wear, improper fit or rings did not seat. Leaky piston/rings is also indicated by heavier smoke on acceleration. Is there blowby out the crankcase vent in the form of oil vapor and/or dripping oil?

[TopDogDave]

thanks for all the input.
most frustratingly it'll have to wait a few months since the bike is in australia 9home) and I'm in Singapore (work).
but when I finally nail the problem I'll post here.
TDD