Compression test diagnosis (was provent disaster)
07-11-2010, 02:01 PM
#16
Nordschleife Master
Your cam timing is not easy to adjust on that car.
With your numbers they aren't too bad and could even be getting lower with a weakening battery. I would recommend that you perform a leakdown test as this will tell you how the rings etc really are.
I have seen perfect compression numbers and not too bad of plugs yet a leakdown clearly shows that the oil control ring was absolutely shot. Cheb (alex popov) had this same issue with his motor recently.
I had one bore in one of my motors get some damage as it appeared the coating on the piston failed. Compression numbers were a little low on that cylinder ( which is suprising once the head came off) but a leakdown clearly showed that cylinder was bad. The plug looked fine too. But I experienced a lot of oil ejection on that motor. I made an air oil seperator with a 5/8" return line to the sump and managed to get straight clean air out of it. But there was a lot of oil going through there and I would need to top it up all the time too.
With your numbers they aren't too bad and could even be getting lower with a weakening battery. I would recommend that you perform a leakdown test as this will tell you how the rings etc really are.
I have seen perfect compression numbers and not too bad of plugs yet a leakdown clearly shows that the oil control ring was absolutely shot. Cheb (alex popov) had this same issue with his motor recently.
I had one bore in one of my motors get some damage as it appeared the coating on the piston failed. Compression numbers were a little low on that cylinder ( which is suprising once the head came off) but a leakdown clearly showed that cylinder was bad. The plug looked fine too. But I experienced a lot of oil ejection on that motor. I made an air oil seperator with a 5/8" return line to the sump and managed to get straight clean air out of it. But there was a lot of oil going through there and I would need to top it up all the time too.
07-11-2010, 02:02 PM
#17
Team Owner
Glen that correct the early cam housing had steel lifter bores and thus the little gaskets fitted to them . If the figure 8s get put on then the newer style cam gaskets then they can lever the tower and thus create a leaking edge these figure 8 gaskets are paper thin so look carefully to sii if they have been fitted, In my case the tower was leaking along both top edges of the tower as there are less bolts to anchor it,
once the figure 8s were removed the leaks went away
once the figure 8s were removed the leaks went away
07-11-2010, 02:12 PM
#18
Racer
Thread Starter
Thanks Jim I'll look into that.
No Problem Merlin - my fault - My head is not where it should be at the moment with all of this.
So much so I have just realised, like an idiot, I have transposed the compression figures in my spreadsheet, so in the pic on the first post the numbers for bank 1-4 should be bank 5-8. It does still indicate one bank lower than the other so I will look into the timing again.
I have added the correct table here.
Once again thanks for the help - I know it doesn't help any when you are given false info in the first instance. I'll try not to be so dull in future!!
No Problem Merlin - my fault - My head is not where it should be at the moment with all of this.
So much so I have just realised, like an idiot, I have transposed the compression figures in my spreadsheet, so in the pic on the first post the numbers for bank 1-4 should be bank 5-8. It does still indicate one bank lower than the other so I will look into the timing again.
I have added the correct table here.
Once again thanks for the help - I know it doesn't help any when you are given false info in the first instance. I'll try not to be so dull in future!!
Last edited by heliflyer; 03-20-2012 at 07:20 AM.
07-11-2010, 02:13 PM
#19
Nordschleife Master
With regards to the leak(s).
The stock gaskets are paper thin for the cam housings as you well know.
I have found that if you have ANY junk in the threads of the bolts it CAN tear the gasket and cause a leak.
There was 1 fellow with a 944 I did a headgasket for him. Bolted it all up and everything was fine.
He went back in there later and removed a couple of the bolts (didnt remove the housing), and that was enough to cause a leak. He took it to a shop that specialises in these cars. They did it twice and it leaked both times. I told him whe he took it back to them that I said to make sure that the bolts threads were 100% clean. They thought this was strange, but did it anyway and the problem has NEVER returned. If Porsche had made the gaskets with the holes being 1-2mm larger in diameter this would not be a problem.
But as was said make sure those figure 8 gaskets are not the problem either.
The stock gaskets are paper thin for the cam housings as you well know.
I have found that if you have ANY junk in the threads of the bolts it CAN tear the gasket and cause a leak.
There was 1 fellow with a 944 I did a headgasket for him. Bolted it all up and everything was fine.
He went back in there later and removed a couple of the bolts (didnt remove the housing), and that was enough to cause a leak. He took it to a shop that specialises in these cars. They did it twice and it leaked both times. I told him whe he took it back to them that I said to make sure that the bolts threads were 100% clean. They thought this was strange, but did it anyway and the problem has NEVER returned. If Porsche had made the gaskets with the holes being 1-2mm larger in diameter this would not be a problem.
But as was said make sure those figure 8 gaskets are not the problem either.
07-11-2010, 02:19 PM
#20
Racer
Thread Starter
No figure of 8 gaskets fitted as my towers have the integral sleeves.
Lizard - thanks for that. I will plan on doing a leakdown test regardless, and will then set about removing and resealing the camtowers using new gaskets (again !) and hondabond or equivalent.
Lizard - thanks for that. I will plan on doing a leakdown test regardless, and will then set about removing and resealing the camtowers using new gaskets (again !) and hondabond or equivalent.
07-11-2010, 04:55 PM
#21
Team Owner
you should not need any hondabond for the 16 valve cam tower .
that info was for a 32V engine
that info was for a 32V engine
07-11-2010, 05:26 PM
#22
Rennlist Member
Rennlist Site Sponsor
As a matter of interest, a faulty oil ring will often cause HIGHER compression in that cylinder. The faulty ring will leave more oil on the cylinder walls, which will basically change a dry test to a wet test for that cylinder.
I rebuilt a Corvair engine with all new GM cylinder units - cylinders, pistons, rings, etc., all factory-set and ready to install. Twenty thousand miles later, oil consumption went from a quart every ten thousand miles to a quart every hundred miles virtually overnight. I was running a use test for a new synthetic oil, so the oil manufacturer and I were both anxious to find the cause. (They were sponsoring my SCCA rally activities.)
A compression test showed that I no longer had the normal 145 psig readings - the lowest cylinder was 195 psig, the highest 225 psig! A teardown revealed that the oil control rings in all six cylinders were totally worn out, while the compression rings were barely broken in. Faulty from the factory...
I rebuilt a Corvair engine with all new GM cylinder units - cylinders, pistons, rings, etc., all factory-set and ready to install. Twenty thousand miles later, oil consumption went from a quart every ten thousand miles to a quart every hundred miles virtually overnight. I was running a use test for a new synthetic oil, so the oil manufacturer and I were both anxious to find the cause. (They were sponsoring my SCCA rally activities.)
A compression test showed that I no longer had the normal 145 psig readings - the lowest cylinder was 195 psig, the highest 225 psig! A teardown revealed that the oil control rings in all six cylinders were totally worn out, while the compression rings were barely broken in. Faulty from the factory...
07-11-2010, 07:19 PM
#23
Racer
Thread Starter
Hmmm... do you think a leakdown test would have shown you the problem before tearing down the engine?
My concern is cylinder 5 that shows very little change between dry or wet although as you pointed out earlier, this is more likely to be a valve issue.
My concern is cylinder 5 that shows very little change between dry or wet although as you pointed out earlier, this is more likely to be a valve issue.
07-11-2010, 08:46 PM
#24
Rennlist Member
Rennlist Site Sponsor
OK, a recap of what I understand - but remember, I have given this minimal attention (my apologies for that).
Car ran fine, no excessive oil consumption, moderate blue (oil) smoke. Problem was coolant loss, etc., so head gaskets were changed. No change in running, oil consumption or smoke.
Added ProVent system, probably not to best design. Car runs fine, moderate oil smoke. Massive blow-by, massive oil loss. No internal indication of a problem (plugs are all very good to excellent with one possible good plug), good compression, no noises, etc.
My first try would be to return the oil ventilation to stock and run it for a few miles. If the massive blow-by continues, something has happened. If all is normal again (moderate smoke, minor blow-by), the problem is with the ProVent plumbing.
The cam cover leakage may or may not be related to the blow-by. If the blow-by stops and so does the cam cover leakage, the problem is plumbing. If the cam cover leakage continues, the gaskets may have been blown out by high crankcase pressure.
Make sense?
Car ran fine, no excessive oil consumption, moderate blue (oil) smoke. Problem was coolant loss, etc., so head gaskets were changed. No change in running, oil consumption or smoke.
Added ProVent system, probably not to best design. Car runs fine, moderate oil smoke. Massive blow-by, massive oil loss. No internal indication of a problem (plugs are all very good to excellent with one possible good plug), good compression, no noises, etc.
My first try would be to return the oil ventilation to stock and run it for a few miles. If the massive blow-by continues, something has happened. If all is normal again (moderate smoke, minor blow-by), the problem is with the ProVent plumbing.
The cam cover leakage may or may not be related to the blow-by. If the blow-by stops and so does the cam cover leakage, the problem is plumbing. If the cam cover leakage continues, the gaskets may have been blown out by high crankcase pressure.
Make sense?
07-11-2010, 08:51 PM
#25
Former Vendor
I never understood what those were for. I've spent a good deal of time looking and pondering, and just couldn't get it.
I believe they were required at the beginning and were left out of later 16V 928s. Possibly tied to that change from lifter sleeves to integral sleeves in the towers.
I believe they were required at the beginning and were left out of later 16V 928s. Possibly tied to that change from lifter sleeves to integral sleeves in the towers.
07-11-2010, 09:48 PM
#26
Nordschleife Master
What do you think they were for? They don't make the bores sealed. The oil will just run out the top or bottom. Holds the sleeves up 0.02"? (or whatever)
I've left them off my rebuilds. I found that they were missing, or partially missing, when I took it apart like they weren't actually clamped in place anyways.
I've left them off my rebuilds. I found that they were missing, or partially missing, when I took it apart like they weren't actually clamped in place anyways.
07-12-2010, 02:06 PM
#29
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
Member
I've "recovered" engines in the 1970's US cars where owners had plugged up oil vent hoses, thinking that it would somehow cure the sucky engine running typical to those first EGR systems. The running problems were unaffected but there was oil all over the place.
Fast-forward to your car, where you have very similar symptoms, tied to mods to the crankcase vent system. Somehow you've managed to block some of the normal vapor paths from the crankcase to the intake or atmosphere. From the top of the cam covers, the vent hoses must be open to relieve crankcase pressure. From the oil filler area, again there must be a working vent. Blocking the filler vent means all blowby gasses (and there are ALWAYS some) must go up the oil return passages to the cam cover vents. That means the gasses are counterflowing with the oil, so more oil stays in the heads and gets pushed through the vent hoses on the cam covers. If the cam cover vents on one side are blocked, velocity at the filler vent and the other cam cover similarly increase. The filler area is splashed by oil thrown by the crank, so less other venting means more gasses venting at the filler, and more oil is carried out.
My first suggestion is to find out where the hoses from the engine to the vent can are pinched or blocked, even partially. The factory vent system reintroduces the blowby gasses (relatively inert as far as combustion is concerned) along with any entrained oil, back into the engine intake between the MAF and the throttle plate. That area is normally at or near atmospheric pressure, so no serious scavenging goes on there. If you have a vent on your catch can to atmosphere, be sure it isn't wet with oil. Even a small amount of oil on a vent 'filter' will severely restrict airflow, and from there it's a slippery slope to no ventilation, and oil leaking from places that don't expect pressure in the crankcase like cam cover gaskets, and often crankshaft and camshaft seals.
Search for restrictions, partially pinched hoses, pieces of paper towel that you accidentally left plugging the vent ports, things like that. Hopefully something in your vent can install is to blame, something that doesn't require a tear-down to fix.
Fast-forward to your car, where you have very similar symptoms, tied to mods to the crankcase vent system. Somehow you've managed to block some of the normal vapor paths from the crankcase to the intake or atmosphere. From the top of the cam covers, the vent hoses must be open to relieve crankcase pressure. From the oil filler area, again there must be a working vent. Blocking the filler vent means all blowby gasses (and there are ALWAYS some) must go up the oil return passages to the cam cover vents. That means the gasses are counterflowing with the oil, so more oil stays in the heads and gets pushed through the vent hoses on the cam covers. If the cam cover vents on one side are blocked, velocity at the filler vent and the other cam cover similarly increase. The filler area is splashed by oil thrown by the crank, so less other venting means more gasses venting at the filler, and more oil is carried out.
My first suggestion is to find out where the hoses from the engine to the vent can are pinched or blocked, even partially. The factory vent system reintroduces the blowby gasses (relatively inert as far as combustion is concerned) along with any entrained oil, back into the engine intake between the MAF and the throttle plate. That area is normally at or near atmospheric pressure, so no serious scavenging goes on there. If you have a vent on your catch can to atmosphere, be sure it isn't wet with oil. Even a small amount of oil on a vent 'filter' will severely restrict airflow, and from there it's a slippery slope to no ventilation, and oil leaking from places that don't expect pressure in the crankcase like cam cover gaskets, and often crankshaft and camshaft seals.
Search for restrictions, partially pinched hoses, pieces of paper towel that you accidentally left plugging the vent ports, things like that. Hopefully something in your vent can install is to blame, something that doesn't require a tear-down to fix.
07-12-2010, 02:17 PM
#30
Racer
Thread Starter
Thanks for all the advice and suggestions.
I'll get the leakdown test done in the next few days and I'll double check all the vent lines.
I don't believe that there has been any restriction on the vent lines (either on the stock set up or the provent setup) as in the stock set up all the hoses were either new or carefully cleaned prior to installation, and on the provent set up all the hoses were new and the plumbing was exactly as per the system Dave uses on his sharkvent systems - minus the return to the sump.
Having said that, your point is well taken Dr Bob, so I will double check all of the vent hoses again.
I'll get the leakdown test done in the next few days and I'll double check all the vent lines.
I don't believe that there has been any restriction on the vent lines (either on the stock set up or the provent setup) as in the stock set up all the hoses were either new or carefully cleaned prior to installation, and on the provent set up all the hoses were new and the plumbing was exactly as per the system Dave uses on his sharkvent systems - minus the return to the sump.
Having said that, your point is well taken Dr Bob, so I will double check all of the vent hoses again.
