Piston guided rods -opinions
Thread Starter
Joined: Nov 2001
Posts: 2,486
Likes: 4
From: Orlando, FL
Piston guided rods -opinions Im doing an engine build for my E55 to build something different for a change, and this one poses some interesting challenges.
The factory block has no sleeves, it's got treated bare aluminum bores called "alusil" that requires the piston be coated in a dissimilar material to prevent galling. This limits the flexibility in piston choices, so that combined with the open deck design leaned me in the direction of Steve @ RED and a set of MID Darton sleeves.
Now that the piston will be residing in a more traditional medium, I've got a few options since there is practically nothing available for this platform yet in regards to internals. It's a very popular engine to modify , coming in about a half dozen different cars but most everyone sticks to bolt ons for a multitude of reasons.
The rotating assembly is a piston guided rod design, but since I'm needing both rods and pistons I can do away with it if there's a benefit to doing so. The rods aren't available from the aftermarket, and with the stock ones being forged and surviving in repeated mid ten second cars with 4400+lb race weights there's not a huge demand for them until now.
The crank shares a pin diameter with the popular Honda and circle track racers(1.888) so I'm going to end up running a rod made for something else, and design the pistons to fit instead of waiting for custom orders on both. I can get a set with a BE width very close to the stock AMG rods and just shim the aftermarket pistons up top to remain top guided, or I can leave the extra side clearance in the piston pin and machine the sides of a set of GM BE width rods to have the .020ish I'd want for a traditional crank guided rod.
Can anyone think of a benefit either way? It'll be easier to leave it top guided since I won't have to true the sides of the crank journals where the rods will be- there's not a ton of material to work with but it's doable
The only thing I can think of in regards to the top guided design is that the factory Mercedes PE clearance is pretty tight, in the .0005 range, but it has a trick bushing and piston oilers that help it live with that clearance (plus the added force of the OE supercharger) The new rods not only won't have that bushing, but will be run with twice that clearance, which will increase the available play in the rod if I leave it top guided. I doubt the NASCAR boys run less than a thou of pin clearance however, and the design works for them at much more RPM (but less power ) then this car will run.
Opinions?
The factory block has no sleeves, it's got treated bare aluminum bores called "alusil" that requires the piston be coated in a dissimilar material to prevent galling. This limits the flexibility in piston choices, so that combined with the open deck design leaned me in the direction of Steve @ RED and a set of MID Darton sleeves.
Now that the piston will be residing in a more traditional medium, I've got a few options since there is practically nothing available for this platform yet in regards to internals. It's a very popular engine to modify , coming in about a half dozen different cars but most everyone sticks to bolt ons for a multitude of reasons.
The rotating assembly is a piston guided rod design, but since I'm needing both rods and pistons I can do away with it if there's a benefit to doing so. The rods aren't available from the aftermarket, and with the stock ones being forged and surviving in repeated mid ten second cars with 4400+lb race weights there's not a huge demand for them until now.
The crank shares a pin diameter with the popular Honda and circle track racers(1.888) so I'm going to end up running a rod made for something else, and design the pistons to fit instead of waiting for custom orders on both. I can get a set with a BE width very close to the stock AMG rods and just shim the aftermarket pistons up top to remain top guided, or I can leave the extra side clearance in the piston pin and machine the sides of a set of GM BE width rods to have the .020ish I'd want for a traditional crank guided rod.
Can anyone think of a benefit either way? It'll be easier to leave it top guided since I won't have to true the sides of the crank journals where the rods will be- there's not a ton of material to work with but it's doable
The only thing I can think of in regards to the top guided design is that the factory Mercedes PE clearance is pretty tight, in the .0005 range, but it has a trick bushing and piston oilers that help it live with that clearance (plus the added force of the OE supercharger) The new rods not only won't have that bushing, but will be run with twice that clearance, which will increase the available play in the rod if I leave it top guided. I doubt the NASCAR boys run less than a thou of pin clearance however, and the design works for them at much more RPM (but less power ) then this car will run.
Opinions?
Last edited by Whistler; Apr 2, 2013 at 07:55 AM.
