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Thread: Turbo Engine Re-Build
11-03-2019, 01:30 PM #16
I believe I would order pistons .004 over the largest cylinder diameter (3.5540) and hone all the bores to 3.5550. That would lead me to a .003 piston to bore tolerance. Does this sound doable?
11-03-2019, 08:59 PM #17
Wait for the pistons to arrive and then the order of battle will look like this;
● Weigh all pistons, pins etc,
● Measure all piston diameters,
build your bob weight map of components mixing and matching to equalize the bob weights of all piston / connecting rod sets,
● Size each bore to the piston you assigned to it in the bob weight calculation process,
● Clean everything and begin assembling.
Life will be happier (not to mention the engine build) and you won't have nasty looking grinding marks on rods you would prefer not to have done those barbaric things to.
Yesterday, 08:09 PM #18
Here we go! I’m taking my chances on a tube front from Rock Solid Motorsports as well.
Yesterday, 08:18 PM #19
Today, 12:11 AM #20
If your largest measured bore dimension is 3.554 (as you documented) you need to allow for the hone to clean up that largest bore also. That means about an additional 0.001" needs to be removed from the liner bringing it to a diameter of 3.555 inches. Because a standard bore is 3.552 inches the cleaned up bores are actually 0.003" over standard bore (3.552).
Piston manufactures actually cut piston to wall (PTW) clearance into the finished piston so you don't have to or want to do the mental gymnastics to add the PTW clearances to get a finished bore size. The manufacturer already did it for you. That said because of manufacturing variances even on premium CNC manufactured billet pistons like Gibtec's, you can still detect small differences of less than 0.001 inches. This is the reason you still want to fit each piston to its final bore exactly the same as we pin fit wrist pins to pistons.
This is the absolute correct way to manage piston fit on a performance build. It takes more effort but the finished product shows the benefits of the additional attention to detail. Wait for the pistons to arrive, figure out the assembly puzzle to normalize the bob weights across all crankpins without barbaric grinding on rods and other premium components. Tell your crank balancer what bob-weight you want your crank balanced to and then hone the cylinders to fit the pistons you have assigned to individual cylinders.
p.s. Remember when you are measuring anything with a micrometer your body heat will be added to what ever you hold in your hand whether it is a mic or a piston. I recommend using a fixture to hold the piston and then measuring it's size. It doesn't take much body heat to change the size of an aluminum piston by 0.001". Not only that but when you hold the mic, it is absorbing your body heat also and it is changing it size also.
Best practices will use a fixture to hold the piston and when you hold the mic you will hold it for the least amount of time possible with the fewest number of fingers possible. As soon as you have measured the piston, you should set the mic back down onto a heavy top, temperature stable table made of aluminum, steel or granite and not touch it until you are ready to measure the next piston.
Today, 04:29 AM #21
Thanks Ed! I’m taking it to a machine shop this week to verify the bores can be cleaned up with a hone, then will place the call to gibtec and let him know my final bore size. Glad he has to do the math instead of me!
I’ve been told to give a 4-6 week lead time for pistons, so I want to take my time pulling the old one apart, fix up a couple issues, and I’m really debating Kevin’s idea for a oil bypass regulator for feeding turbos.
Today, 10:56 AM #22
Sometimes Gibtec can give you an early delivery at this time of year so the anticipated 4 to 6 week delivery could get shortened up possibly to something less than 4 weeks.
Be careful about machine shops.
Many think in standard bore size increments of 10/20 or unbelievably 30 thousandths of overbore for these engines. If you find your shop thinks that way you will either have to help him find new religion (improbable) or you will need to find a new machine shop (much better choice) that will follow your direction and fit each piston to its final bore destination finishing the bores in 0.001" increments for uniform piston to wall (PTW) clearance. Also be cautious about shops that tell you to bore the block first and order the pistons second. These guys view you the way farmers view sheep. The farmer is after the sheep's wool and the machine shop is after your money. It will not be a good experience for either of you and more importantly you will get your engine's cylinder bores sized incorrectly.
When you encounter shops like these, the basic value for value exchange you entered into with the shop will have been breached by the shop but they will still demand payment because they are coming from a close enough is good enough mentality. If you have the slightest inkling that your shop behaves this way just politely leave and find a new shop. Arguing with them about how to do the job will have no effect on what they do and it will piss off both of you. It is a real world example of the old saying about, you can bring a horse to water but you can't make him drink.
Another one to be cautious of is, the use of torque plates. Make sure they use them and use your head studs torqued to the spec you will be using (ARP 2000 studs to either 85 or 90 ft/lbs) and importantly the torque plates need to have gaskets between the head and the block. Used gaskets are fine but the gaskets must be used to duplicate what the block will see at final assembly or else your bores are not going to be round. All these sorts of things represent extra steps for the shop in the completion of the work you are purchasing and for many shops steps they don't like to take because of the extra effort and time. Again if your machinist or shop is sitting in the wrong pew in the wrong church don't waste your time trying to change his religion — find another machinist with the right religion.
BTW if you have a first name I'll use it instead of your screen name,
Today, 11:24 AM #23
Thanks again Ed, I had a nice long talk with them and they have a well understanding on minimizing the enlargement of the bores beyond stock size. They are also well versed on aluminum blocks and sleeve wall thicknesses. Unfortunately, mod motors aren’t their cup of tea.
However, like our conversation, regardless of make, model, shape, or size, the same principals hold true. I’ll have the old gaskets ready to go by the anticipated time of arrival on pistons. All I wanted from this shop initially is to get a second professional opinion on what it’s going to take to get them nice and shiny!
Today, 12:16 PM #24
I understand, Matthew Stay close to them. While principles remain unchanged the idiosyncrasies of various manufactures engines can call for special attention during preparation and final machining / assembly. Those 'special' preps do not always translate across manufacturers. Sounds like you have a good handle on it though.
Today, 12:27 PM #25
I had a good mentor! I will check on torque plates, I wonder if I’ll have to supply them....
Today, 01:13 PM #26
If the shop is a credible shop they should understand the importance of them and already have them, Matt — sort of like stones for hone, it is a shop responsibility and investment in the business if they want to do these types of engines. You should not be required to get them or pay for the shop getting them. That is all part of and included in the price of the honing. If your shop assesses a fee for the use of the plates or does not have the plates it becomes yet another decision point where the question, is this the right service provider, needs to be addressed.