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Piston/ring combination
- Thread starter nhmort
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Riken rings are Pro-X, they don't make Pro-X boxed rings.
Now, an an entire different tangent you really shouldn't use aftermarket pistons (WSM. PRO-X) on a DI.
The reason is that the DI is a really lean burn engine with much higher piston crown temperatures than a standard 2-stroke. The factory pistons have an actual proprietary hard coating on them to deal with these high temperatures.
One of the old time Seadoo Gurus Bill O'neil actually did testing back when the DI came out and kept having pistons melt down on rebuilt DI's, this is when he realized the special factory coating that the aftermarket pistons don't have.
I can't say how long the pro-x or other aftermarket pistons will last but I wouldn't trust them in mine.
Now, an an entire different tangent you really shouldn't use aftermarket pistons (WSM. PRO-X) on a DI.
The reason is that the DI is a really lean burn engine with much higher piston crown temperatures than a standard 2-stroke. The factory pistons have an actual proprietary hard coating on them to deal with these high temperatures.
One of the old time Seadoo Gurus Bill O'neil actually did testing back when the DI came out and kept having pistons melt down on rebuilt DI's, this is when he realized the special factory coating that the aftermarket pistons don't have.
I can't say how long the pro-x or other aftermarket pistons will last but I wouldn't trust them in mine.
Here is is from Mr. Bill, it's long but a good read.
"
As for what piston is the very best for a DI 947, which is much different than a std. carbureated 947 engine, is far and away a better choice to use the oem pistons.
Having fought through the broken ring lands of a variety of brand new DI pistons from several aftermarket companies within the first hour or two of use in a few rebuilt DI motors , I was motivated to do some reasearch as to what is the best piston to use, and how to prevent the ring lands from snapping off directly in front of the exhaust port in the DI clyinder, as even oem pistons can suffer that syndrome before and after boring out a DI clyinder.
The DI was designed to lower emmissions and use much less fuel than is the carbureated engine, which has long been a dinosour to modern day engine designers who were forced by mandates and the list of facts that there is only so much oil in the world that at the rate it is being used up, and the projected growth for the need for natural resourses such as oil in the future, plus the emmissions problems that are choking our atmosphere, governments around the world are joining together to attempt to put a cap on emmissions and the use of petroulem based fuels to power future forms of personal transportation. In the meantime, engine designers were looking for ways to use new, at the time, technology in their previously designed two stroke engines. The two stroke was popular for such vechicles that needed a compact, light, but powerfull engine, like pwc's, atv's, smaller motorcycles, scooters, and other forms of small motorized items like tools such as the chainsaws and garden equipt. Until very recently, there were few choices for a lightweight, small packaged but powerfull four stroke engine to replace the two stroke.
Enter the Orbital designed direct fuel injection, i.e. DI fuel injection, plus electronic engine management systems.
Now back to the pistons for the DI engines. Although they look similiar to the pistons you find in a carbureated engine, they are different in many ways.
The direct fuel injection brought on a boat load of problems for the engineers to overcome when designing a piston that would last in a DI two stroke motor to the standards of Rotax, a renowned Austrian engine building company who subcontracts and builds parts and pieces for Porsche, Mercedes, BMW, Audi and many other of the finest engines ever built.
The government low emmissions mandates required a lean burn engine, which is a polar opposite of the carbureated two stroke engines that most all of us have set our standards to when rebuilding pwc engines. Myself, like so many others, thought we could just build up a DI the same as we could any other 947 engine, and we would have the same result when we finished.
What is called a "lean burn engine" is an engine with a very high rate of detonation that takes place in the clyinders when the engine is tuned properly. Detonation is something that happens in every engine as it is running, but it is controlled detonation and limited by the ignition timing curves, compression ratio, engine running temps, and the octane of the fuel that is being injected into it.
Because a carbureated engine will perform well with a very much richer air/fuel mixture, as back then emmissions were allowed to be higher when carbureated engines were the only form of engines we knew and used, and still do use, the piston technology dating back decades was still being used in our engines right up to the point that such companies as BRP started using DI technogoly exclusively, and phased out the carbureated engines completely. A by product of a rich air/fuel mixture is piston crown and combustion chamber cooling, and the resulting overall cooler running engines. All pluses for controlling detonation in an engine, and having success using lower quality pistons in engines.
My guess is that the aftermarket piston companies did not spend the money to re-design the complete piston, but instead, just followed what they could see on the oem DI pistons, and that was the fact they were coated pistons. In fact, not only coated, but both friction and therminal coated. None of those aftermarket companies really know the forumlas used by Rotax to create those coatings, so the ones that do offer coated pistons are coating them with the standard coatings that are available to anyone.
That is one difference between an oem and an aftermarket piston. There are others too. When designing a product to withstand the rigors and the destruction that is caused by detonation, they needed a piston that could run at much higher tempetures, that would expand in a controlled manner, and that would not pull the wrist pin bosses out of the piston, nor beat the wrist pin roller bearings to death, or allow them to get so hot that the lubrication would break down that lubricates the wrist bearings and the piston skirts.
What I found, was that rebuilding the DI per the oem manual specs for bore size and piston clearances, and using the oem oversized piston, We could rebuild the DI without problems.
Now, here is where the aftermarket pistons come in.
Because very few of the DI clyinders could be cleaned up with a .010 oversized piston ( the largest oversize that the oem sells ), We were forced to go to aftermarket pistons or the only other recourse was to resleeve and go back to the oem orginal bore size.
Because resleeving is expensive for anyone not in that business and capable of making their own sleeves or buying sleeves in huge quanities, our only option was using the aftermarket pistons. The problem was, after trying pretty much all brands available, and different clearances, plus cutting out materials from the combustion chambers, thicker head gaskets, we still had problems breaking off the piston's ring land in front of the exhaust port. Now, if it were only one motor having that problem, I would suspect that the fuel injection system, cooling system or the ignition system was at fault, which is exactly what I did suspect on the first couple of rebuilds that failed prematuerly. But, guess what ? That got me nowhere.
Now, I was scratching my head and at a complete loss for an answer. So, I started asking around with folks that I know in the business as to just how they were handling this problem. Most came back saying " I wish I knew" or something to that effect. But, the more I asked the more bits I was able to put together, and the best answer was "buy a new clyinder" or "resleeve to std ", but that was not what I needed to hear, so I kept asking.
So far, we have been able to overbore and use aftermarket pistons successfully by making a minor change in the initial ignition timing, retarding 1 to 2 degrees, Keeping the compression ratio no higher than the orginal oem compression ratio, and allowing for an extra thousanths in. of piston clearance. Along with that, I drill into the customers head that he needs to keep a close eye on his fuel to be sure he allways buys his fuel from a very busy name brand station and he never pumps anything but the best gasoline that the station has and allways 91 octane or better. Also, that he only uses synthetic oil that meets or exceeds the oem specifications. I tell them that their fuel injection system has to be kept clean and debris free, and that normal service intervals are mandatory. The last thing I tell them is to get their use out of it and then sell the DI before it breaks down again.
Besides that, The machinist who bores our clyinders is capable of boing a perfectly round hole through the sleeves, and he has a two ton floor mounted precision honing machine, filtered cutting oils, with the same 4 sets of stones ( 3 for cutting and 1 for break-in honing ) that would be used by an oem speciality division for a high quality, high rpm engine such as those produced by TRD ( Toyota racing engines or Honda racing engines ).
He understands how to properly build racing engines and he has the best measuring equiptment and the skill and knowledge to use his equiptment properly and with accuracy. For this, I pay him well for doing our machine work.
Our last few DI's have held up well using SBT DI coated pistons, the same pistons they use in their remanufactured engines.
I would never trust a motorcycle shop or a dealership for this type of precision machine work, which IMO, is mandatory to properly rebuild a DI engine in a small shop like ours.
That is my three cents on the subject, but I am open to any comments that may help us build an even better engine for the DI, but, I also look forward to not seeing many more coming into the shop.
Bill O'Neal
WCM "
"
As for what piston is the very best for a DI 947, which is much different than a std. carbureated 947 engine, is far and away a better choice to use the oem pistons.
Having fought through the broken ring lands of a variety of brand new DI pistons from several aftermarket companies within the first hour or two of use in a few rebuilt DI motors , I was motivated to do some reasearch as to what is the best piston to use, and how to prevent the ring lands from snapping off directly in front of the exhaust port in the DI clyinder, as even oem pistons can suffer that syndrome before and after boring out a DI clyinder.
The DI was designed to lower emmissions and use much less fuel than is the carbureated engine, which has long been a dinosour to modern day engine designers who were forced by mandates and the list of facts that there is only so much oil in the world that at the rate it is being used up, and the projected growth for the need for natural resourses such as oil in the future, plus the emmissions problems that are choking our atmosphere, governments around the world are joining together to attempt to put a cap on emmissions and the use of petroulem based fuels to power future forms of personal transportation. In the meantime, engine designers were looking for ways to use new, at the time, technology in their previously designed two stroke engines. The two stroke was popular for such vechicles that needed a compact, light, but powerfull engine, like pwc's, atv's, smaller motorcycles, scooters, and other forms of small motorized items like tools such as the chainsaws and garden equipt. Until very recently, there were few choices for a lightweight, small packaged but powerfull four stroke engine to replace the two stroke.
Enter the Orbital designed direct fuel injection, i.e. DI fuel injection, plus electronic engine management systems.
Now back to the pistons for the DI engines. Although they look similiar to the pistons you find in a carbureated engine, they are different in many ways.
The direct fuel injection brought on a boat load of problems for the engineers to overcome when designing a piston that would last in a DI two stroke motor to the standards of Rotax, a renowned Austrian engine building company who subcontracts and builds parts and pieces for Porsche, Mercedes, BMW, Audi and many other of the finest engines ever built.
The government low emmissions mandates required a lean burn engine, which is a polar opposite of the carbureated two stroke engines that most all of us have set our standards to when rebuilding pwc engines. Myself, like so many others, thought we could just build up a DI the same as we could any other 947 engine, and we would have the same result when we finished.
What is called a "lean burn engine" is an engine with a very high rate of detonation that takes place in the clyinders when the engine is tuned properly. Detonation is something that happens in every engine as it is running, but it is controlled detonation and limited by the ignition timing curves, compression ratio, engine running temps, and the octane of the fuel that is being injected into it.
Because a carbureated engine will perform well with a very much richer air/fuel mixture, as back then emmissions were allowed to be higher when carbureated engines were the only form of engines we knew and used, and still do use, the piston technology dating back decades was still being used in our engines right up to the point that such companies as BRP started using DI technogoly exclusively, and phased out the carbureated engines completely. A by product of a rich air/fuel mixture is piston crown and combustion chamber cooling, and the resulting overall cooler running engines. All pluses for controlling detonation in an engine, and having success using lower quality pistons in engines.
My guess is that the aftermarket piston companies did not spend the money to re-design the complete piston, but instead, just followed what they could see on the oem DI pistons, and that was the fact they were coated pistons. In fact, not only coated, but both friction and therminal coated. None of those aftermarket companies really know the forumlas used by Rotax to create those coatings, so the ones that do offer coated pistons are coating them with the standard coatings that are available to anyone.
That is one difference between an oem and an aftermarket piston. There are others too. When designing a product to withstand the rigors and the destruction that is caused by detonation, they needed a piston that could run at much higher tempetures, that would expand in a controlled manner, and that would not pull the wrist pin bosses out of the piston, nor beat the wrist pin roller bearings to death, or allow them to get so hot that the lubrication would break down that lubricates the wrist bearings and the piston skirts.
What I found, was that rebuilding the DI per the oem manual specs for bore size and piston clearances, and using the oem oversized piston, We could rebuild the DI without problems.
Now, here is where the aftermarket pistons come in.
Because very few of the DI clyinders could be cleaned up with a .010 oversized piston ( the largest oversize that the oem sells ), We were forced to go to aftermarket pistons or the only other recourse was to resleeve and go back to the oem orginal bore size.
Because resleeving is expensive for anyone not in that business and capable of making their own sleeves or buying sleeves in huge quanities, our only option was using the aftermarket pistons. The problem was, after trying pretty much all brands available, and different clearances, plus cutting out materials from the combustion chambers, thicker head gaskets, we still had problems breaking off the piston's ring land in front of the exhaust port. Now, if it were only one motor having that problem, I would suspect that the fuel injection system, cooling system or the ignition system was at fault, which is exactly what I did suspect on the first couple of rebuilds that failed prematuerly. But, guess what ? That got me nowhere.
Now, I was scratching my head and at a complete loss for an answer. So, I started asking around with folks that I know in the business as to just how they were handling this problem. Most came back saying " I wish I knew" or something to that effect. But, the more I asked the more bits I was able to put together, and the best answer was "buy a new clyinder" or "resleeve to std ", but that was not what I needed to hear, so I kept asking.
So far, we have been able to overbore and use aftermarket pistons successfully by making a minor change in the initial ignition timing, retarding 1 to 2 degrees, Keeping the compression ratio no higher than the orginal oem compression ratio, and allowing for an extra thousanths in. of piston clearance. Along with that, I drill into the customers head that he needs to keep a close eye on his fuel to be sure he allways buys his fuel from a very busy name brand station and he never pumps anything but the best gasoline that the station has and allways 91 octane or better. Also, that he only uses synthetic oil that meets or exceeds the oem specifications. I tell them that their fuel injection system has to be kept clean and debris free, and that normal service intervals are mandatory. The last thing I tell them is to get their use out of it and then sell the DI before it breaks down again.
Besides that, The machinist who bores our clyinders is capable of boing a perfectly round hole through the sleeves, and he has a two ton floor mounted precision honing machine, filtered cutting oils, with the same 4 sets of stones ( 3 for cutting and 1 for break-in honing ) that would be used by an oem speciality division for a high quality, high rpm engine such as those produced by TRD ( Toyota racing engines or Honda racing engines ).
He understands how to properly build racing engines and he has the best measuring equiptment and the skill and knowledge to use his equiptment properly and with accuracy. For this, I pay him well for doing our machine work.
Our last few DI's have held up well using SBT DI coated pistons, the same pistons they use in their remanufactured engines.
I would never trust a motorcycle shop or a dealership for this type of precision machine work, which IMO, is mandatory to properly rebuild a DI engine in a small shop like ours.
That is my three cents on the subject, but I am open to any comments that may help us build an even better engine for the DI, but, I also look forward to not seeing many more coming into the shop.
Bill O'Neal
WCM "
Sportster-2001-951C-Stock
Well-Known Member
Make sure you have the correct cylinders as well, the there are at least two port window configurations which prompted MPEM fuel mapping changes.
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