Porous head

A year ago I bought an early 750 Roadster (with central oil tank). The engine did run well but smoked at a cold start.
Didn't use oil. I rebuild the head. New valves, guides with seal etc. After rebuild it run at first kick. No smoke.
So I thought problem solved, but..... Torgued the head several times and no oil leaks between head and barrel.

After a few runs. It started te smoke again at cold starts. When the engine is hot, no smoke or oil use after a run.
Plugs have good colour after a run of 135 km.
I overfilled the oil tank. Oil out of the air filter. Easy problem, lowered the oil level.

I rerouted the engine breathing and added a breather on the oil tank.
So it seems there's a crack when it's cold. This closes when hot.
When I park the bike, starting it after an hour gives (white) smoke most of righthand muffler.
Yesterday I killed the engine and took the right sparkplug which was oiled.

Now I'm thinking of a porous head. The question is how to recognize one.
All advise is welcome.

Thanks in advance :|

Porous head would certainly be very rare, most likely oil seeping by a poorly fitted loose valve guide.

GB

Valve seal?

Are the carbs oily internally? Could it still be sucking oil from the breather?

As a 750 S owner I remember a buddy telling me you gotta see this at the local metal scrapyard up in Ottawa 40 yrs. ago. So we drove the Nortons over to stare at a pile of about 25 Norton heads sitting in a pile of scrap wrecker yard scrap and the man said they were the junk porous heads . They exist.(ed?).

Since your bike isn't new and a porous head I would expect to have shown up when it was and been corrected I'm not inclined to see that as your problem.

You mention bike smoking initially and was it both sides?
Now it is smoking one side.
If originally one side and is still that one side I'd first replace hollow bolts with regular in oil feeds to the rockers to cut off oil and run for a few minutes to see if smoke stops.
If it does you may have a split intake valve stem seal, that happened to me with a new one, or oil getting around guide. Did you follow the procedure of heating head to extract old and install new guides. Did you put in oversize guides?

If stopping oil to rockers doesn't solve problem you may have a ring problem.
Did you do a compression test? With new valves if the pressures aren't equal rings would be the cause.
There are other possibilities but these are the obvious ones I'd consider first. No need to take anything apart yet.

Norvil, resin pressure injects heads, but i doubt oil can leak into the combustion chambers,

Torontonian said:

As a 750 S owner I remember a buddy telling me you gotta see this at the local metal scrapyard up in Ottawa 40 yrs. ago. So we drove the Nortons over to stare at a pile of about 25 Norton heads sitting in a pile of scrap wrecker yard scrap and the man said they were the junk porous heads . They exist.(ed?).

Click to expand...

I agree that if head porous from the start then would of been trashed or repaired by now. Its possible a fault line has finally worked through of course but highly unlikely. This my 2nd spring on Trixie smoked on start ups then cleared up when warm on hwy, for a few months/1000's miles, then smoked to point of misfires leaving one day and that stopped my trusting her to commute on. Issue found as ring oversize gap but didn't smoke at all til like a year/6000 miles after rebuild. There was a bit of bore score left after a light rehone so she still smoked a bit on start ups and blew Combat wet sump oil out at high speed WOT but last ride she didn't smoke after sitting 3 wks nor left oil puddles on hi-ish speed runs for couple hours. Hopefully now after a few 1000 miles new rings they've worn hone texture back to bed in tight. If its a Commando can't limit thinking to the merely obvious, even if obvious found, don't mean its the only thing doing the same thing.

Theres that there stuff wot yr paint ther insides of it wiff too , to seal .

To all of you thanks for answers and advice.

Only during cold start, both mufflers smoke. RH more than LH. After lets say 5 minutes idling smokes is gone.
During rebuild I put new valve guides in the head which take an oil seal. (The original guides had no oil seal).

The smoking issue is still the same after rebuild. Except the first start after rebuild. No excessive oil in the head I suppose.
Some asked if the inlet of the carbs showed black / greasy. Yes, this came true the breather pipe in airfilter. I blocked this pipe and added another breather on the oil thank. This problem is solved.

Yesterday I inspected the cylinder head again. At the RH side I see a black spot occuring let say between the inlet and outlet rocker box. This worries me, because I'm sure I cleaned the head very good and didn't noticed this spot.

So far I didn't do a compression test. Will see to this next week.

Again thanks for all the advice.

rx7171 said:

Since your bike isn't new and a porous head I would expect to have shown up when it was and been corrected I'm not inclined to see that as your problem.

You mention bike smoking initially and was it both sides?
Now it is smoking one side.
If originally one side and is still that one side I'd first replace hollow bolts with regular in oil feeds to the rockers to cut off oil and run for a few minutes to see if smoke stops.
If it does you may have a split intake valve stem seal, that happened to me with a new one, or oil getting around guide. Did you follow the procedure of heating head to extract old and install new guides. Did you put in oversize guides?

If stopping oil to rockers doesn't solve problem you may have a ring problem.
Did you do a compression test? With new valves if the pressures aren't equal rings would be the cause.
There are other possibilities but these are the obvious ones I'd consider first. No need to take anything apart yet.

Click to expand...

Quote "So far I didn't do a compression test. Will see to this next week."


Whilst not trying to belittle your efforts on trying to find the cause of your bike smoking,
Compression test may prove to be inconclusive.
What you really need to do is a leak down test to see where air is escaping from, if at all.
If porous cylinder head, then beadblasting whole of head to clean it, (with rockers removed e.t.c.) and non-destructive crack testing to pin point where the problem lies.

Hm, clearances of parts and pores in Al head will increase with heat not close up seal up, so way we heat to free stuff there. Bead blast by water soluble media like baking soda or face abraisive particle release on full heating. Head should be heated to like 500'F to smoke off oil in pores as solvents tend to drive surface oil deeper to foul pain layer later. Plain compress test likely not good enough so leak down might clue next expenditures but beware its risky bussiness to lock engine at TDC and way more so just off TDC which is part of this test if TDC don't reveal the leak area. I got fooled hearing air escape out rocker box instead of oil tank or breather as instructions say for non Norton engines. I vote ring bore issue more than head but only way to find out is suffer through some more down time or hire out to fog insects.

Could you explain your alternative oil tank breather? I put mine into a catch bottle from the hole in the air filter area. I don't know that I can help with the smoking, I haven't had that issue. Had my head rebuilt by Memphis Motorwerks.

Dave
69S

Quote:

Could you explain your alternative oil tank breather? I put mine into a catch bottle from the hole in the air filter area. I don't know that I can help with the smoking, I haven't had that issue. Had my head rebuilt by Memphis Motorwerks.

I tapped thread 3/8 Withworth, in the hole at the base plate of the airfilter and plugged this with a bolt (used instead gasket on the thread). Secured the bolt with a whire. Then I drilled a 10 mm hole underneath the oil tank cap. Turned a small pipe of 10 mm at the end 2 mm of 14 mm diameter. (Did this with oil in the tank after making a simple dive which prevented to get metal in the oil. (Used a shell of an old oil can with right diameter)
Put this piece true the filler pipe true the 10 mm hole and secured this with a lockring.
Took a longer hose and connected this from the breather left of the crankcase to the new connection underneath the oil tank cap. Connected the original inlet, which is now the outlet with a hose to a small plastic bottle. From there a hose to the back of the bike. Even after a long run very little moister in the plastic bottle. No oil at the back of the bike.

Thanks, I have an extra tank I've been thinking about operating on. I never liked that breather into the air filter. Probably some pollution requirement. It would be easy for me to block, I tapped a 5/16-24 into it and threaded a stud into it with a hole drilled through the center and use that to bring out to a catch bottle through the front chrome piece. Like you, very little oil/moisture in the bottle, I just let it breathe to the air from the pill bottle between the engine and gearbox. I did buy a proper aluminum catch can, but haven't installed it yet. My air filter breather always leaked in the past, but others say no.

Dave
69S

brayhill54 said:

Now I'm thinking of a porous head. The question is how to recognize one.

Click to expand...

I have an 850 head on my bench which most likely has a porosity leak path from the oil return bore to the RHS intake port - and I very much suspect my Atlas which got the port enlarged to 30mm to suffer from the same problem. I was told by a German engine rebuilder that this is a very common problem on cyl head with port sizes of 30mm and more. However that would explain a leakage on the right cylinder only.

Recognizing is a little difficult especially with the head installed. On the 850 it's actually possible to feel a small cavity, on the 750 I can only see something in that area but the symptoms would be explained by this cavity problem. To be absolutely sure a pressure test would be needed which is what I want to do on the 850. Block the drilling in the fireface and use a blow-out gun with a rubber-tipped extension to reach the drilling next to the valve spring machinings in the head.


Tim