M50b32 12:1

[st.petebiodiesel]

Those JE pistons can't be worse than the stock cast pistons.
Back to the build,
While I waited for my machine shop to bore my block and resurface my head I tinkered around with the oil pump.

As many of you know the oil pump shaft and nut is the weak link in the oil pump. I purchased the Achilles Motorsport oil pump shaft. Swapping the rotor was easy using a vice, just make sure you measure exactly the position of the rotor on the shaft. You will need to press the new shaft into the rotor and you want your chain alignment to be spot on.

Left is the upgraded shaft, Right is OEM

No the safety wire isn't backwards, the nut is L/H thread.
One other thing important to mention that I totally forgot about is using a torque plate.
Anytime you bore or even hone an engine block it's very important to use a torque plate to simulate the stresses of having a head bolted to the block. This stress distorts the bore and causes the cylinders to become egg shaped.

I rented this torque plate from VAC Motorsport. Yes it was expensive, but worth it. It's also important to use whatever head gasket you will be using under the torque plate. So I had to buy a new head gasket just to throw away after the boring was complete. I also had to provide my ARP head studs, thankfully they are reusable.
My machinists measured the bore before and after installing the torque plate and reported a average distortion of .0015".


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[st.petebiodiesel]

M50b32 12:1

So the day finally came when I received everything back from the machine shop.

It only cost $400 to have my block tanked, decked, and bored from 84mm to 86.4mm.
I also had my head resurfaced since I used a cut ring head gasket on my last build.


You can see all the deposits from my crazy blow by issue from before.
First thing to do was set my ring gap. The general rule for the top ring is .005" for every 1" in diameter of bore. 86.4mm = 3.4" x .005 = .017" top ring gap.

The second ring is set at .004"-.008" greater than the top ring gap as per the piston manufacturers instructions.

My next step was to check all the bearing clearances. I bought a new set of Kobelschmidt standard size bearings. The specified factory bearing clearance is .0007" to .002". I was at the higher end of this tolerance at .0016" but still within the factory new limit.


All my clearance looked the same.
Now with my ring gap set and all bearing clearances checked it was time for assembly!!

First insert all the piston cooler nozzles in the bearing bosses and insert the bearings. I'm using Clevite bearing guard as an assembly lubricant. Next drop in the crank, install the caps, and torque to spec 20Nm then 50 degrees. Use all new hardware with the crank and connecting rod fasteners. I couldn't find a published tightening sequence for the bottom end so I just used common sense and gradually increased the torque in a criss cross pattern.
Next the pistons and rods were ready to be installed. I always set my piston ring gaps 180 degrees from each other before piston install. Piston rings do migrate slightly during engine operation so it's not that important, just don't line them all up on the same side of the piston.

Installing the pistons does take a decent amount of force. Sometimes the piston rings will catch on the deck if you do not have your piston ring compressor tight enough. The chances of damaging your rings is very high if you aren't using the proper equipment or don't have experience doing this before. Make sure you have the crank at BDC when installing each piston to avoid scoring the crankshaft journals.

All pistons/rods installed!

Now you can really appreciate the compression of these pistons. They sit .048" above the deck.




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[ForcedFirebird]

You will need to shave the timing cover to match the block.

.048" is a lot. With a stock thickness gasket, this is only going to leave you with .022" between the head and pistons - not nearly enough. Your rod bearings will be destroyed in no time.

[Jaker]

The general rule that I've been taught and applied over the years for ring gap clocking is that you want the gaps to be away from any thrust surfaces and - as you already mentioned - not overlapping. Using the clock with 12 o'clock at the intake side of the engine right between the 2 intake valves, the top ring gap is placed at about 1:30, middle ring gap at about 10:30 and the oil ring spacer at about 7:30 with the top oil scrapper slightly to one side and the bottom one slightly to the other side of the spacer gap.

[st.petebiodiesel]

You will need to shave the timing cover to match the block.

.048" is a lot. With a stock thickness gasket, this is only going to leave you with .022" between the head and pistons - not nearly enough. Your rod bearings will be destroyed in no time.

The piston specs were created by VAC Motorsport, I trust these guys knew what they were doing when designing them. My machine shop decked my front timing cover at the same time as my block.
I understand higher compression engines have to deal with greater stress, but so do forced induction engines.
This engine will likely never see an output over 100hp/liter so I'm sure my bearings will last as long as any other modified M50.


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[digger]

Yeah don't trust VAC in general.

I think he means the bearings will get damaged because the piston will start to tap the head as rpm gets to a certain point due to insufficient clearance between the piston and head. There are different opinions on how close you can go something around 0.040" is good. This would require 0.088" gasket or nearest thickness

[ForcedFirebird]

Yeah don't trust VAC in general.

I think he means the bearings will get damaged because the piston will start to tap the head as rpm gets to a certain point due to insufficient clearance between the piston and head. There are different opinions on how close you can go something around 0.040" is good. This would require 0.088" gasket or nearest thickness

Correct. I have experience with this and can say for sure, .022" is not enough.

[st.petebiodiesel]

Correct. I have experience with this and can say for sure, .022" is not enough.

It may have been an erroneous measurement on my behalf.
I checked my piston spec sheet and my compression height is only .008" higher than a stock S52, which a quick google search came up with 3.7848mm compression height. I know my machine shop wouldn't remove more than .002" resurfacing the block.

I have over 4000 miles on this engine already and beat on it pretty regularly with a 7000 rpm redline. No problems as of yet.


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[ForcedFirebird]

It may have been an erroneous measurement on my behalf.
I checked my piston spec sheet and my compression height is only .008" higher than a stock S52, which a quick google search came up with 3.7848mm compression height. I know my machine shop wouldn't remove more than .002" resurfacing the block.

Depends, but generally don't need more than .002". I have had to go as much as .004"

I have over 4000 miles on this engine already and beat on it pretty regularly with a 7000 rpm redline. No problems as of yet.


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I was mistaken and thinking you are posting as you are building it. I learned about too little quench the hard way, and would hate to see someone ruin an engine in the same manner. I always check it now, the time saved by not measuring cost me a race weekend plus the engine rebuild.

[st.petebiodiesel]

Depends, but generally don't need more than .002". I have had to go as much as .004"



I was mistaken and thinking you are posting as you are building it. I learned about too little quench the hard way, and would hate to see someone ruin an engine in the same manner. I always check it now, the time saved by not measuring cost me a race weekend plus the engine rebuild.

How long did your engine last? Did you find out the quench dimension after the engine failure?
The only part I can see hitting is where the combustion chamber is completely flat. It may be worth borrowing a borescope from work to see if there are any signs of interference.



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[ForcedFirebird]

It lasted ~4 or 5 20-30min practice/test sessions then 3hr of hard racing. Oil pressure was lost and a bearing spun. I did not measure the damaged engine, but it was an m20 and the head was shaved right to the dimples (domed pistons hit the head when shaved too much). I have gone as close as .035" on BMW engines.

Thinking about your measurement comment, perhaps .48mm (.019")?

[st.petebiodiesel]

[QUOTE=
Thinking about your measurement comment, perhaps .48mm (.019")?[/QUOTE]


This seems probable, however I have no way of verifying. I've heard that stock S52 pistons sit about .015" above the block.

Calculating the specs

M50 deck height is 210mm
89.6mm stoke divided by 2 is 44.8mm
Rod length is 135mm
Piston compression height is 30.988mm
44.8+135+30.988=210.788
So theoretically my pistons should be .030" above the deck. This does not take account for how much was removed from the block from resurfacing. So ideally I would have a quench gap of .040", but realistically probably around .038 with the block resurfacing.
I did take this picture before I installed the head. Cylinders 1 and 6 are at TDC.



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[ForcedFirebird]

I have gone as close as .035" on BMW engines.

This seems probable, however I have no way of verifying. I've heard that stock S52 pistons sit about .015" above the block.

Calculating the specs

M50 deck height is 210mm
89.6mm stoke divided by 2 is 44.8mm
Rod length is 135mm
Piston compression height is 30.988mm
44.8+135+30.988=210.788
So theoretically my pistons should be .030" above the deck. This does not take account for how much was removed from the block from resurfacing. So ideally I would have a quench gap of .040", but realistically probably around .038 with the block resurfacing.
I did take this picture before I installed the head. Cylinders 1 and 6 are at TDC.

Sounds perfect then. There is a "1" and "0" press-stamped into the block if you look close (so far, all i6's I broke have them). When the "0" is gone, the block is supposed to be discarded.

Leaving with that thought, I bet a few more points of compression are available with a quick lathe job on the piston crowns and a few more thou off the block deck.

[drew_step]

Have you made any progress on the build? I'm curious to see what sort of power it makes when it's finished.

[Jaker]

Sounds perfect then. There is a "1" and "0" press-stamped into the block if you look close (so far, all i6's I broke have them). When the "0" is gone, the block is supposed to be discarded.

I know this isn't apples to apples, but I took .090" off an aluminum Z3 single Vanos block (unicorn) to clean up some extreme "headgasket failed" erosion and so far (25,000 miles) I've had no issues. I'm running the .140 Cometic gasket and my pistons are designed with this configuration in mind (rings are moved down a bit).