Mysterious SBC Oil leak
Discussion
I had a leak from where the inlet manifold joins with the block. This can with modded heads and inlets like yours be a big gap that is hard to seal with normal gasket gue. I had to get some special gap filling stuff to get rid of mine. The gap is approx 10mm! It takes some actual acceleration to get oil in the valley to slosh back hard and leak but that was my problem.
So had 10 minutes and (almost dry roads) today so..... drum roll.....
Here are the results from running the car down the road:
So unless anyone can explain how I can get engine oil out of that hole in the gearbox I think we can conclusively state that the rear crank oil seal is knackered.
Here are the results from running the car down the road:
So unless anyone can explain how I can get engine oil out of that hole in the gearbox I think we can conclusively state that the rear crank oil seal is knackered.
Yes 100% not gearbox oil. Spins the wheels deep into 3rd gear, so car is in rude health 😃
None of the parts places are open and Peter Knight appears to be shut for Christmas (can't say I blame him), so I'll have to satisfy myself with draining the sump and popping it in readiness. Having investigated rear main seals from Fel-pro there appears to be several options 😒 so will hold out to speak with the guys at Knight - don't want to do this sump removal more than I already have done!
None of the parts places are open and Peter Knight appears to be shut for Christmas (can't say I blame him), so I'll have to satisfy myself with draining the sump and popping it in readiness. Having investigated rear main seals from Fel-pro there appears to be several options 😒 so will hold out to speak with the guys at Knight - don't want to do this sump removal more than I already have done!
V8Dom said:
Might find flywheel casing side is wet..:0)
He is correct.And the clutch right now could be slowly getting saturated. Very often when this goes too far the clutch will be found useless
A slow leak will sometimes find the clutch fine(if caught) with gravity the only savior.
Remember temps often increase when the engine is shut down due to water, but pressure often exists, when the seal cools the oil seeps
This all depends on how far the seal has failed
V8Dom said:
Might find flywheel casing side is wet..:0)
I'd be amazed if that weren't the case. I'm assuming at this stage that the oil is only coming out of the main seal under duress (big revs and the oil in the scavenge pan being pressed up against the rear seal), it then hits the crank 'spider' and it flung up from there. Given enough time i suspect that the fly wheel and clutch would all be soaked in the stuff.The postie delivered a 'standard' seal today but all I've read says it's not suitable for 'race' applications so will have to see what colour/type the seal is when I've stripped it.
Happy New Year to All!
Nabbot: Unfortunately rear main oil seal on the SBC was one of several weak points that the LS corrected. If yours is a two piece seal there is a conversion to a one piece seal that my engine builder says is a much better solution. I always imagined that at some point there was a meeting at G.M. A gaggle of engineers got together and started making a list of items to be corrected in the next generation V8 which we know as the LS. Rear main seal was probably in the top three things on the list. Lee
ROWDYRENAULT said:
Nabbot: Unfortunately rear main oil seal on the SBC was one of several weak points that the LS corrected. If yours is a two piece seal there is a conversion to a one piece seal that my engine builder says is a much better solution. I always imagined that at some point there was a meeting at G.M. A gaggle of engineers got together and started making a list of items to be corrected in the next generation V8 which we know as the LS. Rear main seal was probably in the top three things on the list. Lee
Yes I know 
Trouble is that's probably an engine out job (or at the very least 'box, clutch and flywheel). The two pierce looks like it lasted 10 + years (probably hardening through lack of use accelerated the failure). So all being well it's a 'do it once/do it well' job. Fingers crossed......
Had I had my time again LS3 would be the way I'd go but time and money are always gonna be a factor.
Just one last thing to check before you tear down your engine...
I see you have a dry-sump set up on your small block chevy, coupled with trick cylinder heads and kinsler EFI. This is pretty much exactly the same set up as my own car...and amazingly, I have a similar oil leak when we work the engine very hard!
The odd oil leak doesn't really matter to me, as this particular car is an out and out track-only car, and, put simply I have grown to love the small block chevy and learned to put up with all its little oddities over many years of playing with it.
Typically, if your small block uses a Weaver or similar pump, then space is very limited and will probably restrict you to a 3 stage oil pump, that is one scavenge from both front and back of the oil pan, plus one pressure stage feeding the engine.
I underdrive my oil pump 1 to 2. which means 7000 engine rpm turns the oil pump at 3500 rpm, which pumps a LOT of oil (I have fabricated a 5 gallon oil tank to ensure we always have a proper reserve when the engine is constantly pulling hard).
One of the particular quirks of the small block engine is that, when worked very hard, the oil pumps up and sits in the valley between the cylinder heads, No amount of enlarging of the oil drain holes worked for me, so I am afraid I had to learn all this the hard way, destroying several race engines until I worked out what was actually going on and an eventual solution. Essentially you have not a negative crank case pressure as the theory suggests, but a mass of oil/air being continuously pumped under positive pressure into the valley, sitting up against a 10 mm gap (kinsler EFI manifold to engine block). Every EFI manifold appears slightly different, so each gasket has to be "customised" (read silicon sealer), so we inevitably end up with mild oil "weepage"
After several hard pulls on the dyno after checking the reserve in the oil tank I have seen up to 2 gallons of oil 'missing in action', and therefore sitting in the valley. Idling returns the oil level to normal levels over a period of a few minutes.
For an out and out race engines we now now suck oil straight out of the front of the engine from under the intake and we use a 3rd scavenge stage on the pump. I don't think Ted had this in mind when he designed the chassis, and rather unhelpfully I don't think a 4-stage pump will fit in there.
Can't really see too much definitive info from your oily rag photos, and of course you may indeed have a weeping rear main seal as others have suggested (use the one piece if you do replace), but I couldn't stand by and see you go to all the hassle of pulling the car apart, to then get it back together again and find more oil weeping owing to this rather unique combo which many folks will not come across very often.
Hope this bit of hard-won information helps.
By the way, they do make glorious noises when worked hard, don't they?
I see you have a dry-sump set up on your small block chevy, coupled with trick cylinder heads and kinsler EFI. This is pretty much exactly the same set up as my own car...and amazingly, I have a similar oil leak when we work the engine very hard!
The odd oil leak doesn't really matter to me, as this particular car is an out and out track-only car, and, put simply I have grown to love the small block chevy and learned to put up with all its little oddities over many years of playing with it.
Typically, if your small block uses a Weaver or similar pump, then space is very limited and will probably restrict you to a 3 stage oil pump, that is one scavenge from both front and back of the oil pan, plus one pressure stage feeding the engine.
I underdrive my oil pump 1 to 2. which means 7000 engine rpm turns the oil pump at 3500 rpm, which pumps a LOT of oil (I have fabricated a 5 gallon oil tank to ensure we always have a proper reserve when the engine is constantly pulling hard).
One of the particular quirks of the small block engine is that, when worked very hard, the oil pumps up and sits in the valley between the cylinder heads, No amount of enlarging of the oil drain holes worked for me, so I am afraid I had to learn all this the hard way, destroying several race engines until I worked out what was actually going on and an eventual solution. Essentially you have not a negative crank case pressure as the theory suggests, but a mass of oil/air being continuously pumped under positive pressure into the valley, sitting up against a 10 mm gap (kinsler EFI manifold to engine block). Every EFI manifold appears slightly different, so each gasket has to be "customised" (read silicon sealer), so we inevitably end up with mild oil "weepage"
After several hard pulls on the dyno after checking the reserve in the oil tank I have seen up to 2 gallons of oil 'missing in action', and therefore sitting in the valley. Idling returns the oil level to normal levels over a period of a few minutes.
For an out and out race engines we now now suck oil straight out of the front of the engine from under the intake and we use a 3rd scavenge stage on the pump. I don't think Ted had this in mind when he designed the chassis, and rather unhelpfully I don't think a 4-stage pump will fit in there.
Can't really see too much definitive info from your oily rag photos, and of course you may indeed have a weeping rear main seal as others have suggested (use the one piece if you do replace), but I couldn't stand by and see you go to all the hassle of pulling the car apart, to then get it back together again and find more oil weeping owing to this rather unique combo which many folks will not come across very often.
Hope this bit of hard-won information helps.
By the way, they do make glorious noises when worked hard, don't they?
GT5594
That is exactly my theory although explained in a lot more detail! However the tests that the OP has done seem to show it not to be the case.
I am interested in your comments on 4 stage oil pumps as I am about to convert.
The factory seem to suggest that they always use a 4 stage pump with 3 outlets on the pan.
I agree with your comments re oil build up in the valley but also with their reasons for needing a third outlet on the other side of the pan.
What part of the chassis gets in the way?
I am looking at a 4 stage ARE pump and pan.
Any comments appreciated.
O/T I guess sorry. Still interested in comments. PM me if you like.
That is exactly my theory although explained in a lot more detail! However the tests that the OP has done seem to show it not to be the case.
I am interested in your comments on 4 stage oil pumps as I am about to convert.
The factory seem to suggest that they always use a 4 stage pump with 3 outlets on the pan.
I agree with your comments re oil build up in the valley but also with their reasons for needing a third outlet on the other side of the pan.
What part of the chassis gets in the way?
I am looking at a 4 stage ARE pump and pan.
Any comments appreciated.
O/T I guess sorry. Still interested in comments. PM me if you like.
Edited by MarkWebb on Thursday 1st January 11:00
Great and well thought through response - thanks very much!
I do get a little oil 'sweating' on the valley plates (for all the reasons you outline in your response) - and have resigned myself to this. It isn't a modern engine afterall.
The fact remains that my rear seal is definitely leaking and if not addressed will toast the clutch
I've disconnected the scavenge pipes and drained the sump - new two piece seal is the only option I can retrofit with the engine and box still in the car (limited garage time and an impending house move being chief causes). More on this later
I do get a little oil 'sweating' on the valley plates (for all the reasons you outline in your response) - and have resigned myself to this. It isn't a modern engine afterall.
The fact remains that my rear seal is definitely leaking and if not addressed will toast the clutch
I've disconnected the scavenge pipes and drained the sump - new two piece seal is the only option I can retrofit with the engine and box still in the car (limited garage time and an impending house move being chief causes). More on this later
When I built my engine I was advised that oil would tend to trap in the valley particularly when using the Melling high volume pump.
On this advice I opened out all the return passages and smoothed out all the casting roughness. I then painted all the inner surfaces of the block.
The seal at the back of the valley leaked from day one but improved after I installed the PCV valve.
When I installed the new EFI inlet I started by applying a bridge of sealant along the valley edge then a layer of cling film before fitting the inlet. Once the sealant had set I removed the inlet so I could see if the bridge was well formed and secure. This technique was vindicated because the bridge was not as good as I had hoped so additional sealant was used where required then the final bead before the inlet was installed fully.
Steve
On this advice I opened out all the return passages and smoothed out all the casting roughness. I then painted all the inner surfaces of the block.
The seal at the back of the valley leaked from day one but improved after I installed the PCV valve.
When I installed the new EFI inlet I started by applying a bridge of sealant along the valley edge then a layer of cling film before fitting the inlet. Once the sealant had set I removed the inlet so I could see if the bridge was well formed and secure. This technique was vindicated because the bridge was not as good as I had hoped so additional sealant was used where required then the final bead before the inlet was installed fully.
Steve
The valley certainly fills up when the engine is revved hard continuously, but adding a third scavenge to the oilpan, as suggested, doesn't solve the problem. A third scavenge stage actually needs to pull oil from under the manifold itself, so your magnesium Kinsler inlet manifold would need a #16 hose adaptor fitting. This would mean some judicious skill with a milling machine and 2-pack adhesive plus an Aeroquip hose fitting installed. Access is a problem with this set up. The distributor (yes its an antique engine) is right in the way, preventing the obvious and easy route from the back, which only leaves a small gap under the front (just above the water pump).
If you want perfection, you can still get a pair of 6mm or 8mm thick shaped aluminium filler plates supplied by Kinsler which saves you having to construct a "bridge" as Steve D described having to do on his own engine. You will still need plenty of black silicon sealer to finish things off though...
Normally you should not have to go resort to these mods unless you really are working the engine hard - but the fact you have installed Kinsler EFI certainly suggests you intend to!
Turning to your problem rear seal and working under the car - a couple of tips
You don't say which actual engine block you are running. If you are stuck having to replace the rear main seal with the engine remaining in the car, then you are limited to the 2-piece, but I would strongly recommend that you buy a one piece oil pan gasket. Summit Racing supply both types either for a "standard" type road engine block (these with a casting which has a small "notch" for a dipstick), or alternatively a race-block (without the "notch" in the base of the casting).
Under the car, this job is particularly awkward, and "stressy", as most of the time you are working you are acutely conscious that if you don't get the sump gasket spot on perfect then the bally thing will leak and you will need to do it again. Patience and a nice cup of Yorkshire tea is definitely needed.
The one piece gasket is rubberised with steel inserts, and much easier to use, and I install it dry. To keep the gasket up against the underside of the sump (it will drive you mad by constantly drooping just as you are trying to get the pan in place), I spot it in place in 6-7 places with glue. Goes on a treat then.
Put a straight edge on the facing edges of your dry sump pan before you re-install. Most are steel fabricated pans and see very heavy use. The boltholes stretch and the faces warp and twist easily under engine stresses. Make sure the facing edges are absolutely flat and straight and "adjust" with a hammer as necessary until they are bang on. You can often create your own leaks and oil weepage just by removing and re-installing your own sump!
Good luck with the work. Don't forget the gasket only ever goes straight back on with no messing if you use Yorkshire Tea.
Andrew
If you want perfection, you can still get a pair of 6mm or 8mm thick shaped aluminium filler plates supplied by Kinsler which saves you having to construct a "bridge" as Steve D described having to do on his own engine. You will still need plenty of black silicon sealer to finish things off though...
Normally you should not have to go resort to these mods unless you really are working the engine hard - but the fact you have installed Kinsler EFI certainly suggests you intend to!
Turning to your problem rear seal and working under the car - a couple of tips
You don't say which actual engine block you are running. If you are stuck having to replace the rear main seal with the engine remaining in the car, then you are limited to the 2-piece, but I would strongly recommend that you buy a one piece oil pan gasket. Summit Racing supply both types either for a "standard" type road engine block (these with a casting which has a small "notch" for a dipstick), or alternatively a race-block (without the "notch" in the base of the casting).
Under the car, this job is particularly awkward, and "stressy", as most of the time you are working you are acutely conscious that if you don't get the sump gasket spot on perfect then the bally thing will leak and you will need to do it again. Patience and a nice cup of Yorkshire tea is definitely needed.
The one piece gasket is rubberised with steel inserts, and much easier to use, and I install it dry. To keep the gasket up against the underside of the sump (it will drive you mad by constantly drooping just as you are trying to get the pan in place), I spot it in place in 6-7 places with glue. Goes on a treat then.
Put a straight edge on the facing edges of your dry sump pan before you re-install. Most are steel fabricated pans and see very heavy use. The boltholes stretch and the faces warp and twist easily under engine stresses. Make sure the facing edges are absolutely flat and straight and "adjust" with a hammer as necessary until they are bang on. You can often create your own leaks and oil weepage just by removing and re-installing your own sump!
Good luck with the work. Don't forget the gasket only ever goes straight back on with no messing if you use Yorkshire Tea.
Andrew
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