RV8 Oil Leak/Lack of Power
Discussion
Can I just bounce this off the great and knowledgeable.
I retired from he race at Oulton on Saturday with oil pissing out of the rocker covers onto the exhaust and very little power once it started to rev.
It has been commented that the car sounded very quiet, and devoid of V8 burble.
One theory, that I'm going to investigate tonight is that the exhaust is blocked, potentially due to a collapsed cat. Would this cause such a great increase in back pressure that the restriction is causing a large amount of blow-by on the exhaust stroke, pressurising the crankcase and forcing oil out of the weakest seal, in this case the rocker cover seals. At the moment I'm running the standard recirculating breather system.
Any thoughts? Tonight I'm going to chop the dustbin open and see what the cat is upto, failing that its got a rodent nesting in the main system, or one of the dogs balls, seeing as the exhaust system has been stored behind the shed all winter.
Thanks in advance
Regards
Iain
I retired from he race at Oulton on Saturday with oil pissing out of the rocker covers onto the exhaust and very little power once it started to rev.
It has been commented that the car sounded very quiet, and devoid of V8 burble.
One theory, that I'm going to investigate tonight is that the exhaust is blocked, potentially due to a collapsed cat. Would this cause such a great increase in back pressure that the restriction is causing a large amount of blow-by on the exhaust stroke, pressurising the crankcase and forcing oil out of the weakest seal, in this case the rocker cover seals. At the moment I'm running the standard recirculating breather system.
Any thoughts? Tonight I'm going to chop the dustbin open and see what the cat is upto, failing that its got a rodent nesting in the main system, or one of the dogs balls, seeing as the exhaust system has been stored behind the shed all winter.
Thanks in advance
Regards
Iain
Step one cut up a dead lambda sensor and make yourself an exhaust backpressure gauge.
Can you see excessive blow-by if you take the oil filler cap off?
Do you see simmilar blow-by from the breather if you disconnect it? (Blocking throttle body etc)
All quick and easy to check relative to exhaust off and cutting open.
Can you see excessive blow-by if you take the oil filler cap off?
Do you see simmilar blow-by from the breather if you disconnect it? (Blocking throttle body etc)
All quick and easy to check relative to exhaust off and cutting open.
Thanks Peter, I can't recall how many times I've said that!!!
What do you use as a gauge for the modified lambda sensor pressure sensor thingy??? a length of clear tube and a bit of water???
I've taken onboard the suggestions and will try them, de-catting was on the to do but never got round to list so I'll probably do that anyway!
Regards
Iain
What do you use as a gauge for the modified lambda sensor pressure sensor thingy??? a length of clear tube and a bit of water???
I've taken onboard the suggestions and will try them, de-catting was on the to do but never got round to list so I'll probably do that anyway!
Regards
Iain
Hi Andy, it is a serpentine front end. I know there is the old adage that just becasue its new, doesnt mean it's not faulty, but the whole front timing chest was replaced during the rebuild, so a fresh oil pump relief valve etc. The gauge is reading a maximum of 55psi or so (using Valvoline VR1 20w-50 oil) when reved, so nothing excessively high, i've seen pressures go up to 90psi with a blocked relief valve.
Is the cat on your car the band clamp flange or the bolted flange type?
Regards
Iain
Is the cat on your car the band clamp flange or the bolted flange type?
Regards
Iain
When the cat melted on mine the engine would idle happily but felt like it switched off as soon as the power built up. It would sit at full throttle at 2000 rpm with the boost gauge off the dial. The cat lit up like a christmas tree, too. Close the throttle and it was happy as anything. Point was that the backpressure totally killed the power, and even under these extreme conditions nothing unusual happened in terms of blow-by, crank pressure etc.
It's worth measuring the back pressure anyway, first to rule this out and second to give you a reference point next time this comes up. I expect you'd be looking at 3-4 psi of back pressure. I just used 12" of steel pipe as a heat sink and then plumbed in an ordinary boost gauge I happened to have lying around. I suppose you could use a manometer if you wanted (3 psi represents 0.2 bar or roughly a 6' head of water) but for the sake of a few quid a proper gauge would save you a lot of hassle.
Back to the symptoms, if the breather was blocked that might account for the oil leak but not the power loss. If you had a major piston sealing problem that could produce so much blow-by that the contamination on the intake became an issue. Hard to believe it would get this bad without going bang though, anyway a compression and leakdown test would soon rule this out.
It's worth measuring the back pressure anyway, first to rule this out and second to give you a reference point next time this comes up. I expect you'd be looking at 3-4 psi of back pressure. I just used 12" of steel pipe as a heat sink and then plumbed in an ordinary boost gauge I happened to have lying around. I suppose you could use a manometer if you wanted (3 psi represents 0.2 bar or roughly a 6' head of water) but for the sake of a few quid a proper gauge would save you a lot of hassle.
Back to the symptoms, if the breather was blocked that might account for the oil leak but not the power loss. If you had a major piston sealing problem that could produce so much blow-by that the contamination on the intake became an issue. Hard to believe it would get this bad without going bang though, anyway a compression and leakdown test would soon rule this out.
chassis 33 said:
I retired from he race at Oulton on Saturday with oil pissing out of the rocker covers onto the exhaust and very little power once it started to rev.
Iain
It would take a lot of pressure to blow all the seals. You're suggesting back pressure has blown up the valve stems and into the engine cavity instead of pushing through the cat. I'd find that hard to accept but hey, I'm wrong sometimes. Have you got stem seals? Did the dipstick blow out oil, did the crank seal blow out oil, are your catch tanks full? If not, then the rocker leak is a seperate issue.
I can't help but think a pcv system would be a lot better then open breathers. At least the crankcase would be in a state of vacuum, sucking air in where you may have a dodgy seal.
Boosted.
ok, taking one step back for a moment, assuming they are two separate issues, and ignoring the exhaust issue for a moment, what would cause such a leak from the rocker gaskets?
It is a fresh engine, but i have checked the rocker bolts are tight. Could the leak be purely due to crap gaskets, now not for one moment do i intend to suggest the guy who's built it for me has used substandard parts, however which are prefered for rocker gaskets, cork or rubber?
Now the exhuast/power problem, with no load the engine revs relatively cleanly however the moment it's n gear and trying to pull through the rev range it starts off fine then really struggles, the higher it revs/the more load is applied to the engine, which suggests to me it is a restriction to the volume flow rate of the exhaust gasses. Also gas is being blown out of the joints between the headers and the dustbin, even when cleaned up, and sealed with Firegum.
Regards
Iain
It is a fresh engine, but i have checked the rocker bolts are tight. Could the leak be purely due to crap gaskets, now not for one moment do i intend to suggest the guy who's built it for me has used substandard parts, however which are prefered for rocker gaskets, cork or rubber?
Now the exhuast/power problem, with no load the engine revs relatively cleanly however the moment it's n gear and trying to pull through the rev range it starts off fine then really struggles, the higher it revs/the more load is applied to the engine, which suggests to me it is a restriction to the volume flow rate of the exhaust gasses. Also gas is being blown out of the joints between the headers and the dustbin, even when cleaned up, and sealed with Firegum.
Regards
Iain
chassis 33 said:
really struggles, the higher it revs/the more load is applied to the engine, which suggests to me it is a restriction to the volume flow rate of the exhaust gasses. Also gas is being blown out of the joints between the headers and the dustbin, even when cleaned up, and sealed with Firegum.
Blowing the exhaust gaskets out does support the theory that it's back pressure related. Other possible causes are fuel starvation, or an obstruction in the intake - collapsed pipework perhaps. Something this dramatic should be easy enough to track down by elimination.
chassis 33 said:
ok, taking one step back for a moment, assuming they are two separate issues, and ignoring the exhaust issue for a moment, what would cause such a leak from the rocker gaskets?
It is a fresh engine, but i have checked the rocker bolts are tight. Could the leak be purely due to crap gaskets, now not for one moment do i intend to suggest the guy who's built it for me has used substandard parts, however which are prefered for rocker gaskets, cork or rubber?
Now the exhuast/power problem, with no load the engine revs relatively cleanly however the moment it's n gear and trying to pull through the rev range it starts off fine then really struggles, the higher it revs/the more load is applied to the engine, which suggests to me it is a restriction to the volume flow rate of the exhaust gasses. Also gas is being blown out of the joints between the headers and the dustbin, even when cleaned up, and sealed with Firegum.
Regards
Iain
First off I'd bond the rocker gaskets to the covers using hermatite or something similar. Then they will seat properly. I like the cork gaskets. When you remove the covers you may find out why they are leaking. As for the pressure in the exhaust system, well it needs double checking to test your theory. I'd also check ignition timing and camshaft timing. Whatever is wrong will be found if you're methodical so you could write up a short list of things to check.
Boosted.
Ok folks, as suggested the oil leak and lack of power are totally isolated. The (rubber) gasket around the rockers was poorly fitted by myself so I must take the blame for that.
The power issue, seems to stem from a faulty fuel pressure regulator (the standard issue type), causing excess pressure in the rail. The rich running has produced a load of soot which seems to of blocked the main cat.
The current state of play is the rockers have been sorted, the regulator replaced from by a known good unit and the dustbin is currently in two halves needing re-welding.
Hoping to fire it up over the weekend and see how things look and feel then. While the dustbin is open is there any benefit to be had modifying the internals of the void to help gas flow, either by a plate baffle running top to bottom to keep the two banks of exhaust gas separated for longer or reducing the volume (sleaving it to reduce the diameter)of the dustbin etc etc?
Regards
Iain
The power issue, seems to stem from a faulty fuel pressure regulator (the standard issue type), causing excess pressure in the rail. The rich running has produced a load of soot which seems to of blocked the main cat.
The current state of play is the rockers have been sorted, the regulator replaced from by a known good unit and the dustbin is currently in two halves needing re-welding.
Hoping to fire it up over the weekend and see how things look and feel then. While the dustbin is open is there any benefit to be had modifying the internals of the void to help gas flow, either by a plate baffle running top to bottom to keep the two banks of exhaust gas separated for longer or reducing the volume (sleaving it to reduce the diameter)of the dustbin etc etc?
Regards
Iain
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