Wiseco Pistons / Bore Wear / Oil Consumption
Discussion
Just wondering if anyone has any opinions on the following issue with a freshly built race/track engine. The head has been removed to investigate an excessive oil consumption problem under wide throttle openings/heavy load. This is seen as blue smoke out of the exhaust as you load up the engine. There is no smoke on overrun. The engine has only been used for approximately 15-20 hours.
The engine is a BMW M50, cast iron block, originally 84mm bore. It has Wiseco 84.5mm pistons installed. The machine shop asked for the pistons and Wiseco specification sheet before machining. Piston to bore clearance is specified by Wiseco as 0.0035" (0.0889mm). Block was bored and finish honed.
Once the block had been machined, I gapped the rings to spec for my application (circuit use), and clocked them as per Wiseco documentation. Oil rail supports were also included with this specific piston, which were installed under the oil control ring pack.
The engine was ran in on the dyno with Millers Competition "Running In" Oil. The engine was then tuned and produced a healthy 315hp/285lbft. I had no reason to believe anything was wrong at this point.
Normal "super unleaded" pump fuel is used, no race fuel or additives. The engine is ran on standalone management. I data log all aspects of this engine including EGTs and wideband O2. I run dual knock sensors and record actual engine noise at all times. The engine has never been ran excessively rich, I target 12.5:1 wide open throttle, and over the course of the above 15-20 hours running have seen nothing out of the ordinary in the logs. This engine is always between 4000-7500rpm and oil pressure is good.
There is no PCV/CCV system in place, the engine uses ITB and the crankcase breather/vent is piped to a catch can, which in turn vents to atmosphere. The catch can remains empty with no actual liquid present, just a small amount of vapor on the walls. The intake tracts, ports and valves all appear dry and no evidence of oil entering there. Valve stem seals were new at rebuild (Supertech) and are all present with their tension rings still in place.
Over the 15-20 hours running the engine has consumed approximately 2L of oil per day on circuit. It has got no better, nor any worse. Actual engine performance was still as it was the first time it was used = good. Before removing the head, I compression tested the engine at 210-215psi evenly across all siz cylinders.
After removing the head, all six cylinders appear to have been polished to a mirror finish on both intake and exhaust side of the bore, some as far as there being no visible honing remaining. Here are a few pictures:
Could this be the cause of the oil consumption? As at the moment I have found nothing else "wrong". What could be the cause of this wear, considering the engine was performing well at the time? Incorrect boring to the block leaving too much piston to wall clearance? Incorrect oil control rings? Unfortunately my bore gauge does not measure above 75mm so I am unable to verify the bore dimension myself just yet, I trusted the machine shop to do this part correctly.
Any ideas would be appreciated.
The engine is a BMW M50, cast iron block, originally 84mm bore. It has Wiseco 84.5mm pistons installed. The machine shop asked for the pistons and Wiseco specification sheet before machining. Piston to bore clearance is specified by Wiseco as 0.0035" (0.0889mm). Block was bored and finish honed.
Once the block had been machined, I gapped the rings to spec for my application (circuit use), and clocked them as per Wiseco documentation. Oil rail supports were also included with this specific piston, which were installed under the oil control ring pack.
The engine was ran in on the dyno with Millers Competition "Running In" Oil. The engine was then tuned and produced a healthy 315hp/285lbft. I had no reason to believe anything was wrong at this point.
Normal "super unleaded" pump fuel is used, no race fuel or additives. The engine is ran on standalone management. I data log all aspects of this engine including EGTs and wideband O2. I run dual knock sensors and record actual engine noise at all times. The engine has never been ran excessively rich, I target 12.5:1 wide open throttle, and over the course of the above 15-20 hours running have seen nothing out of the ordinary in the logs. This engine is always between 4000-7500rpm and oil pressure is good.
There is no PCV/CCV system in place, the engine uses ITB and the crankcase breather/vent is piped to a catch can, which in turn vents to atmosphere. The catch can remains empty with no actual liquid present, just a small amount of vapor on the walls. The intake tracts, ports and valves all appear dry and no evidence of oil entering there. Valve stem seals were new at rebuild (Supertech) and are all present with their tension rings still in place.
Over the 15-20 hours running the engine has consumed approximately 2L of oil per day on circuit. It has got no better, nor any worse. Actual engine performance was still as it was the first time it was used = good. Before removing the head, I compression tested the engine at 210-215psi evenly across all siz cylinders.
After removing the head, all six cylinders appear to have been polished to a mirror finish on both intake and exhaust side of the bore, some as far as there being no visible honing remaining. Here are a few pictures:
Could this be the cause of the oil consumption? As at the moment I have found nothing else "wrong". What could be the cause of this wear, considering the engine was performing well at the time? Incorrect boring to the block leaving too much piston to wall clearance? Incorrect oil control rings? Unfortunately my bore gauge does not measure above 75mm so I am unable to verify the bore dimension myself just yet, I trusted the machine shop to do this part correctly.
Any ideas would be appreciated.
Krikkit said:
Was the finish hone and piston size thoroughly checked on assembly? What were the measurements?
Unfortunately not by myself at the time. My bore gauge does not go over 75mm. The machine shop asked for the pistons and paperwork with the block. I (maybe unfortunately) trusted them, and paid them to do that job correctly and size the bores accordingly. Pistons came back numbered to the bores.
Tye Green said:
buy a bigger bore gauge to start with....
Thanks. Easy to say now after I trusted the machine shop to do the job I paid for correctly.I don't see anything you've done wrong, but that bore wear shows something is badly wrong. The oil consumption also points to a scraper ring problem. I can't suggest what the problem is but a careful measurement of the pistons and bores might give a clue. Does this block distort much when the heads are fitted?
Although it doesn't seem to be getting any worse yet, if that rate of wear continues it will surely be knackered quite soon - and dumping metal into the oil the whole time. Have you had the oil analyzed?
Although it doesn't seem to be getting any worse yet, if that rate of wear continues it will surely be knackered quite soon - and dumping metal into the oil the whole time. Have you had the oil analyzed?
GreenV8S said:
I don't see anything you've done wrong, but that bore wear shows something is badly wrong. The oil consumption also points to a scraper ring problem. I can't suggest what the problem is but a careful measurement of the pistons and bores might give a clue. Does this block distort much when the heads are fitted?
Although it doesn't seem to be getting any worse yet, if that rate of wear continues it will surely be knackered quite soon - and dumping metal into the oil the whole time. Have you had the oil analyzed?
I have not inspected the oil/filter yet, I have yet to drain the sump. I wouldn't normally start stripping the engine down in-situ but I was basically looking for "the problem" and got this far.Although it doesn't seem to be getting any worse yet, if that rate of wear continues it will surely be knackered quite soon - and dumping metal into the oil the whole time. Have you had the oil analyzed?
With regards to distortion - from previous reading I think most generally regard the iron block (like this) to be the most tolerant against it. I do use ARP head studs. From what I have seen people are only using torque plates for boring when going up to larger bore sizes 86mm+. The M52 alloy blocks are a different matter and its generally agreed to always use a torque plate for these.
The back story of this block was it had been honed multiple times in the past without issue, running stock sized pistons (84mm), and stock rings, but we were near the end of the standard tolerances. When it was decided to rebuild the engine, the obvious choice was up the bore to the next available size, 84.5mm and bump the compression (it is now 12.5:1, vs 10.2:1 before) at the same time with forged pistons.
Bore finish can be hit or miss....often miss resulting in high oil consumption.
In some cases I've had more oil use than if I'd just hit it myself with a DIY hone....c'est la vie.
Probably not a fault of the piston, rings ( unless they were installed wrong )....just the bore finish supplied, assuming clearance is correct.
In some cases I've had more oil use than if I'd just hit it myself with a DIY hone....c'est la vie.
Probably not a fault of the piston, rings ( unless they were installed wrong )....just the bore finish supplied, assuming clearance is correct.
f0xy said:
Krikkit said:
Was the finish hone and piston size thoroughly checked on assembly? What were the measurements?
Unfortunately not by myself at the time. My bore gauge does not go over 75mm. The machine shop asked for the pistons and paperwork with the block. I (maybe unfortunately) trusted them, and paid them to do that job correctly and size the bores accordingly. Pistons came back numbered to the bores.
Tye Green said:
buy a bigger bore gauge to start with....
Thanks. Easy to say now after I trusted the machine shop to do the job I paid for correctly.
Legacywr said:
The narrative on the bore gauge suggested…?
Just a generic copy+paste description they use on all listings.A cheap tool like that may or may not be worth using, you'd have to validate it against a known-good one imho.
Or spend x2 and run the same loop https://www.amazon.co.uk/Draper-Expert-02753-50-16...
Krikkit said:
Just a generic copy+paste description they use on all listings.
A cheap tool like that may or may not be worth using, you'd have to validate it against a known-good one imho.
Or spend x2 and run the same loop https://www.amazon.co.uk/Draper-Expert-02753-50-16...
I actually thought the eBay link was a joke to be honest, considering the Chinese listing etc. A cheap tool like that may or may not be worth using, you'd have to validate it against a known-good one imho.
Or spend x2 and run the same loop https://www.amazon.co.uk/Draper-Expert-02753-50-16...
My current bore gauge is Mitutoyo, but just not large enough for cylinder bores. I only usually really use it for connecting rod and crankshaft journals. So in all honesty I'd just buy the next size up and have both - I've just never needed one this size until now.
I'm looking to borrow one short term to verify the bores, but no doubt I will buy one to confirm cylinder bores myself after machine work is done next time regardless.
AW111 said:
I had a similar issue with a professionally built engine once.
Teardown showed that one of the rings was installed upside down - on every piston!
Wonderful...! The top two rings on these pistons were marked for top side and I installed/double checked them, so know they are correct in this case. The oil control rings were instructed to be installed either way, no markings. Teardown showed that one of the rings was installed upside down - on every piston!
stevieturbo said:
Seen it done myself too....and think I did it once myself on a piston lol.
But bore finish is usually the culprit.
I need to pull the bottom end out now and strip it apart to see if anything obvious is wrong with the rings, as well as measure the bores which will be easier on a stand anyway.But bore finish is usually the culprit.
What types of bore "finish" are recommended for X Y Z? I can't say I've ever specified what finish I specifically wanted to said machine shop for work in the past...
stevieturbo said:
Bore finish can be hit or miss....often miss resulting in high oil consumption.
In some cases I've had more oil use than if I'd just hit it myself with a DIY hone....c'est la vie.
Probably not a fault of the piston, rings ( unless they were installed wrong )....just the bore finish supplied, assuming clearance is correct.
See it time and time again, honing is hard work and expensive so x machine shop leaves half a thou if they can bore it that accurately and then tickle the hone up and down to disguise the machine marks and make it smooth to touch… Or they genuinely don’t know what they are doing. Of course every machine shop will tell you they have never had a problem, doing it for years, diamond stones are different etc etc.In some cases I've had more oil use than if I'd just hit it myself with a DIY hone....c'est la vie.
Probably not a fault of the piston, rings ( unless they were installed wrong )....just the bore finish supplied, assuming clearance is correct.
Result is engine burns oil, wears out due to lack of oil retention or even knocks out a piston.
f0xy said:
What types of bore "finish" are recommended for X Y Z? I can't say I've ever specified what finish I specifically wanted to said machine shop for work in the past...
It's a complicated answer, of which I am not qualified to detail. However I know this, very few machine shops have the right equipment to do a great job....and none have what the OEM's have.And bore finish can depend on the type of rings you intend to use.
It isn't to say machine shops cannot do a good job, some can...but it just seems very difficult to find them. In most cases an average job is usually fine though. And as I've said, I've had times myself where a DIY drill/hone has sealed better than a machine shop hone.
Which is very disappointing and leaves you rather disillusioned. No doubt there are countless videos on youtube about it all.
https://www.youtube.com/watch?v=k_5LANVzWe8
https://www.youtube.com/watch?v=LIfbYd9cqcs
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