Good info on running without Balance shafts with some pics
06-05-2011, 03:30 PM
#1
Burning Brakes
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Good info on running without Balance shafts with some pics
Ok so it is possible to very cheaply remove the balance shafts and run without them on the 944 engine.
To do so, I remove the balance shafts, but keep the housings in place along with the front bearing housings.
I machine the front bearing housings flat. You can do this with an angle grinder and a nice big single cut file and be flat enough if you are very careful, otherwise have it milled flat.
Make a gasket, and a metal plate in the shape of the front bearing cover. Use the original M8 bolts and bolt your gasket and plate down on the front. You could even use some Permatex Ultra-Grey here if you are worried.
To seal the oil ports in the block that originally supplied oil to the balance shafts you'll need to use an NPT plug. That means drilling, which means metal contaminants which means you should probably do this when you have the motor out of the car and upside down on a stand, where the metal shavings will fall back out at you rather than down into your oil pan.
A 1/8" NPT plug very nearly is a perfect size for this oil port. I used this one:
http://www.mcmaster.com/#brass-pipe-...d-pipe/=cm94uu
And the proper drill bit (very little material will be removed from the hole because it is almost already the right size.) The proper size is a Q or R drill bit. Q will give a tighter fit. Oh, and a 1/8" NPT quality hand tap.
Insert the plug, and use loctite 272 (red) or equivalent strong threadlocker that is oil and heat resistant. Tighten in as hard as you feel safe.
VIOLA!! You're done. Much cheaper than any conversion kit.
Running without the balance shafts HAS CREATED vibrational problems. At certain RPM's vibrations now develop distinctly and strongly over about a 3-500 RPM range and then dissipate just as suddenly. These 'out of balance' RPM points can be felt by placing my hand firmly on the shifter and running the engine through the RPM's. The vibrational patches at low RPM's aren't very strong, but at cruising speed the amplitude of the harmonic becomes SEVERE. My tach is currently not yet working from the engine transplant, but this harmonic comes on suddenly at 70mph in my car with 245/40/17 wheels and a 924S transmission in 5th gear. It won't go away until I'm doing about 85.
If I can pilfer some accelerometers from my lab at school and fix my tach, I can get some more precise data. But until then, I would recommend using the hand on shifter technique to feel for the bad vibration RPM bands and STAY OUT of them. Aircraft engines mark the tachometers with yellow tics throughout the range indicating that you can pass the engine through that RPM band but never cruise in it for prolonged periods. This is for the same problem as I now have in my 944 motor. Vibration.
In conclusion, this is a clever mod, that comes at a cost. Those vibrations are definitely strong enough to break something, and I'm feeling them from near center on the crankshaft. They would be worse at the oil-pan/ fuel rail. When I'm not in a bad RPM patch, then engine is smooth as it ever was. This mod won't decrease your ride quality and it gets rid of that annoying whine, and makes services easier. Fine mod for a track car as you are never at one RPM for long. Highway cruising is another story!! Stay out of the bad spots if you want to not crack your oil-pickup or fatigue some random critical part.
Hope this was helpful to everyone!!
To do so, I remove the balance shafts, but keep the housings in place along with the front bearing housings.
I machine the front bearing housings flat. You can do this with an angle grinder and a nice big single cut file and be flat enough if you are very careful, otherwise have it milled flat.
Make a gasket, and a metal plate in the shape of the front bearing cover. Use the original M8 bolts and bolt your gasket and plate down on the front. You could even use some Permatex Ultra-Grey here if you are worried.
To seal the oil ports in the block that originally supplied oil to the balance shafts you'll need to use an NPT plug. That means drilling, which means metal contaminants which means you should probably do this when you have the motor out of the car and upside down on a stand, where the metal shavings will fall back out at you rather than down into your oil pan.
A 1/8" NPT plug very nearly is a perfect size for this oil port. I used this one:
http://www.mcmaster.com/#brass-pipe-...d-pipe/=cm94uu
And the proper drill bit (very little material will be removed from the hole because it is almost already the right size.) The proper size is a Q or R drill bit. Q will give a tighter fit. Oh, and a 1/8" NPT quality hand tap.
Insert the plug, and use loctite 272 (red) or equivalent strong threadlocker that is oil and heat resistant. Tighten in as hard as you feel safe.
VIOLA!! You're done. Much cheaper than any conversion kit.
Running without the balance shafts HAS CREATED vibrational problems. At certain RPM's vibrations now develop distinctly and strongly over about a 3-500 RPM range and then dissipate just as suddenly. These 'out of balance' RPM points can be felt by placing my hand firmly on the shifter and running the engine through the RPM's. The vibrational patches at low RPM's aren't very strong, but at cruising speed the amplitude of the harmonic becomes SEVERE. My tach is currently not yet working from the engine transplant, but this harmonic comes on suddenly at 70mph in my car with 245/40/17 wheels and a 924S transmission in 5th gear. It won't go away until I'm doing about 85.
If I can pilfer some accelerometers from my lab at school and fix my tach, I can get some more precise data. But until then, I would recommend using the hand on shifter technique to feel for the bad vibration RPM bands and STAY OUT of them. Aircraft engines mark the tachometers with yellow tics throughout the range indicating that you can pass the engine through that RPM band but never cruise in it for prolonged periods. This is for the same problem as I now have in my 944 motor. Vibration.
In conclusion, this is a clever mod, that comes at a cost. Those vibrations are definitely strong enough to break something, and I'm feeling them from near center on the crankshaft. They would be worse at the oil-pan/ fuel rail. When I'm not in a bad RPM patch, then engine is smooth as it ever was. This mod won't decrease your ride quality and it gets rid of that annoying whine, and makes services easier. Fine mod for a track car as you are never at one RPM for long. Highway cruising is another story!! Stay out of the bad spots if you want to not crack your oil-pickup or fatigue some random critical part.
Hope this was helpful to everyone!!
06-05-2011, 04:36 PM
#2
Rainman
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if i had the engine apart and had some wonky way to deal with the vibrations, i'd just weld the oil holes closed on the block and ditch the covers entirely...
why does your 944S have fuel lines on the driver side?
why does your 944S have fuel lines on the driver side?
06-05-2011, 06:17 PM
#4
Lazer Beam Shooter
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06-05-2011, 09:59 PM
#6
Burning Brakes
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Yes earlier chassis - swapped motor hence the fuel lines from the drivers side.
You do not want to get rid of the covers too. They structurally support the block. You could weld the aluminum ports for the oil shut. Some people don't have their welders set up to do aluminum.
I could make a video - but you wouldn't notice the vibration in it. The car hides it pretty well. Put your hand on the shifter - which is rigidly bolted to the engine and then you'll feel it!
You do not want to get rid of the covers too. They structurally support the block. You could weld the aluminum ports for the oil shut. Some people don't have their welders set up to do aluminum.
I could make a video - but you wouldn't notice the vibration in it. The car hides it pretty well. Put your hand on the shifter - which is rigidly bolted to the engine and then you'll feel it!
