Moorron
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 posted on 14/8/08 at 02:18 PM |
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turbo rebuids
Hi there, I’m looking for some advice on the causes of a smoking car, first off its my CBR1000F engined kit car which I have added a turbo to it and I
am 99% convinced it’s the turbo.
The problem was there before I rebuilt the turbo but now it’s a lot worse, Basically the car smokes heavily at idle (seems to get clearer when I hold
the revs up) and is sporadic and sometimes clears itself for a few seconds. It looks like white smoke but its not water as i am not loosing any, oil
and water are not mixing also. The turbo is about 2” above the oil level so i am sure its not oil building up in the turbo from not being able to
drain quickly enough. Ive added a 1mm restrictor into the oil feed line to limit the oil supply to the turbo, so I have 25psi at idle but an unknown
flow rate. Oil is passing into the exhaust system thru the turbo because the manifold looks dry.
Has anyone here got any experience in rebuilding turbo’s and how the ‘piston ring’ type seal on the exhaust side works?
I understand i am taking a risk doing the rebuild myself regarding the balancing of the unit, but I thought I would give it a go as this is the locost
builders way. The rebuild went fine, but as soon as it was fitted it smoked A LOT! I googled the problem and all seems to point to a knackered exhaust
side seal on the turbo, or it was because the exhaust pressure is low and the oil is being drawn out caused by a straight thru exhaust. Luckily I have
a more restrictive R1 baffled unit so I put that on and it did jack and still smoked. I took it apart again last night to have a look thinking I have
damaged the seal when first fitting it but all looks fine, HOWEVER looking at the instructions It doesn’t state if the gap of the seal should be
orientated to the top of the turbo. I placed it at the top and turned the shaft by hand and then removed it to see if the seal moves with the shaft or
stays put, it didn’t so I assume it stays at the orientation you fit it at, if this is the case does it matter which way it goes?. I am going to try
again tonight but i am looking for some advice to why my turbo leaks oil before I take a hammer to it.
To sum up my gibberish above:-
1, how does the seal work in the exhaust side of the turbo?
2, If the gap was put at the bottom would oil pass it and thus cause my problem?
3, Does anyone know how much oil is required to feed the turbo (how long to fill up a jam jar from the oil feed)?
Thanks guys.
Andy
Sorry about my spelling, im an engineer and only work in numbers.
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MikeRJ
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| posted on 14/8/08 at 04:44 PM |
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The seal works purely through very close tolerances, it's more like a labyrinth seal than a traditional rubber oil seal. The better designed
ones have staggered ends rather than straight to improve sealing in this area. The sealing ring must be a close fit into the groove machined into the
turbine shaft, any wear here and a new seal won't help. Likewise any damage to the machined surface which the outside of the ring seals to will
cause problems.
Have you checked any crankcase breathers are clear and working properly? Any pressure in the crankcase will make oil less willing to return from the
turbo.
Did you measure radial and axial float on the turbo before and after rebuild?
Does your set-up include an intercooler? If so have to flushed it out to ensure there is no build up of oil within it?
[Edited on 14/8/08 by MikeRJ]
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Moorron
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| posted on 14/8/08 at 06:40 PM |
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Hi, all the intercooler and pipework is still left off the car so the turbo is just spinning in free air at the moment.
But things look worse now, tonight it smoked again, i tooked the turbo off which was soaking in oil on the turbine side and looked at it closer, there
is oil in the inlet of the turbine meaning it looks like oil is comming out the engine but the manifold is bone dry, also inside the head ports on the
exhaust side are bone dry too.
So i thought i would run the engine without the manifold or turbo on, i placed a filler cone in the pipe which returns oil to the sump and left the
oil feed above it.
When the engine is cranked over oil rises from the oil return filling the cone half way (so now the oil level is above the turbo centre), add to this
alot of oil coming out of the oil feed and im sure when its at idle the turbo is submerged in oil. I dont know if this has caused the oil to
'splash' into the turbo inlet or that i do have oil going thru the engine?
I then did the same with the oil feed going to a seperate filling jug and it filled about 1 pint in 20-30 seconds. is this still way too much oil
passing thru here? im amazed its filling so fast considering its passing thru a 1mm hole. Maybe i need to go to a 0.5mm hole to limit the supply
further?
So now im thinking is the sump pressurising from knackered internals to rise the oil level in the return?, strange thing is when i hold it at a faster
idle the oil level drops in the return pipe, wouldnt this be the other way round if the sump was pressurising?
Plenty of oil is getting to the top of the engine.
The engine runs fine and with it running with the manifold off there was no smoke.
Im confused now, is it the engine or the turbo.
ps, when i rebuilt the engine earlier in the year i fitted a new oil pump, could it be leaking causing it to pump oil right back into the sump and
just by luck my return pipe is getting a surge from the returning oil?
hmmmmmmmm!
[Edited on 14/8/08 by Moorron]
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MikeR
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| posted on 14/8/08 at 07:01 PM |
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this might seem daft, what if you make the oil supply hole bigger.
1mm is really small and might be making a lot of pressure in the oil system somewhere - this is forcing the oil the wrong way round the system and
therefore you've got your problem.
(no, i know this doesn't make sense due to the fact its coming from the sump - the implication to me is pressurised engine and therefore
i'd guess blocked breathers)
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Moorron
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| posted on 14/8/08 at 07:19 PM |
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The engine is a motorbike crb100f version, it doesnt have a sump breather so im assuming it just vents up thru the centre of the engine past the
camchain and then into the heads breather into my catch tank (its free i checked).
Regarding the oil supply, ive taken it off the oil pressure switch location so i cant see it creating a problem.
Cheers tho, the sump is coming off so i can check the various oil lines inside the sump so see if they are broken or loose. I might also check the
relief valve, but it seems to be holding pressure ok.
Sorry about my spelling, im an engineer and only work in numbers.
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locoR1
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| posted on 14/8/08 at 07:42 PM |
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Sound very similar to the problems I had in the first year with mine but mine would only smoke on overrun.
The first thing I tried due to the turbo being very low and marginal on the oil return being high enough was an electric scavenge pump unfortunately
made no difference.
As the oil was finding its way into the exhaust housing I fitted a rebuild kit again no difference even though the turbo looked and felt fine before
and after the rebuild.
Then eventually and reluctantly after spending all summer messing about with it and leaving smoke screens every where I went took the plunge and
brought a new turbo .
Never had a problem since! Now looking back I should of just put a new one on right from the start.
 
Description
Check out my CB500T Cafe Racer build diary
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Moorron
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| posted on 14/8/08 at 08:19 PM |
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im not sure, if only i could show you what i mean, i have the turbo off the car, oil return pipe still attached to the sump (top of it is about
1.5" about full oil level). What i crank the engine over about 3 seconds after oil starts flowing out of the oil return pipe in other words its
going the wrong way! which means oil is getting pushed by pressure or flow up it.
I think the turbo is fine, i just think its getting flooded becuase of this engine problem.
i need to check the compression tomorrow and see if its off. If it is i have damaged something in the 50 miles i have done after new piston and rings
were fitted.
with newly hooned bores do i get blow-by until its smoothed the bores and bedded in? or have i broke it again
Sorry about my spelling, im an engineer and only work in numbers.
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locoR1
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| posted on 14/8/08 at 09:39 PM |
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Sounds very strange! Wouldn’t of expected any substantial blow by on cranking,
Just looking through your photo archive have you only got the one breather? That filter on your breather tank looks very restrictive.
As part of my attempts to sort mine before I fitted the new turbo I made an adapter and put a second breather on the oil filler
Description
Check out my CB500T Cafe Racer build diary
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Moorron
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| posted on 14/8/08 at 10:44 PM |
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looking into the head thru the plug holes shows wet looking piston tops. Im checking the compression tomorrow, if that looks ok im going to take the
sump off and have a look about.
The breather filter looks like a typical industrial breather, was on the car when i got it but i do notice a lot of moisture from it lately.
i could add one, but its got so much clearance around the cam chain i might just take the rocker cover off and start it up.
there is something in the back of my mind, when fitting the piston rings i couldnt id the top side of the second ring, maybe i have fitted it the
wrong way round?
last bit will be taking the head off, i dont really want to do this again if i can help it.
sigh!
[Edited on 14/8/08 by Moorron]
Sorry about my spelling, im an engineer and only work in numbers.
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MikeRJ
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| posted on 15/8/08 at 01:53 AM |
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quote:
Originally posted by Moorron
strange thing is when i hold it at a faster idle the oil level drops in the return pipe, wouldnt this be the other way round if the sump was
pressurising?
Oil is getting pumped out of the sump more quickly at higher engine speeds, so you have more oil in the rest of the engine. The fact that you get
smoke at idle (when sump level is at it's highest) points to the oil drain from the turbo being a problem.
You do get a bit more blowby with new rings and honed bores. I doubt a single piston ring is causing the problems, but a compression check would
show if all the cylinders are sealing ok.
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