I had to tear down my TT .61 Pro due to the front bearing going out. When I removed the head, the liner was stuck to the head with both the dome and the piston having a lot of carbon build-up. I put all of it in a crockpot anti-freeze bath on high for a couple of days - the liner finally came off the head and everything cleaned up nice and clean, which lead to the problem.

When I was removing everything from the crockpot my wire marker on the piston/rod noting which direction was forward snagged on another engine block and came off. The best way I found to align it to what I think is the correct position was to look for the round wear marks that should be on the front side of the rod where it would brush against the crank, but they are so faint it's hard to tell. But when I do this I notice the last bit of carbon that wouldn't come off the piston is towards the exhaust, but on the head it's away from the exhaust.

So my question is, not being able to determine which way was forward on the piston/rod assembly, will this cause a wear issues on the rod bottom end (which appeared to have a very even wear on the bearing) and/or piston/liner wear? Or should I pull the piston out and turn it 180 deg. so the carbon stains match the stains on the head? This engine has great compression and pulls very hard (tached 13,800 with an APC 12 X 6 on 10% fuel with bad bearings) and I don't want to tear it up.

Hogflyer

Typically the piston has a darker area to wards the ehaust port.

The big end of the rod has a chamfer or taper to the bushing on the side that goes towards the crankshaft. On the opposite side the are generally swirl marks on the rod from where it has rubbed the back plate?

That's where my thinking was the carbon build-up would be heaviest towards the exhaust. There aren't any discernible wear marks on the backplate, so I went with the small circular wear area around the rod bushing where it would contact the crank which also puts the carbon remains towards the exhaust.

Hogflyer

Sounds good to me

One thing I have noticed has to do with the wrist pin in the piston. Sometimes the con rod will slide further towards one side of the piston than the other. The side that is slides most to is the rear. The reasoning is that this is to assemble and disassemble the engine! Attempting to put it in backwards sometimes won't work because of not enough play to get the con rod on the crank pin.
I don't remember if this is the case with the Pro 61 or not but I thought I'd mention it. I've looked for the swirl marks too!

Does the big-end of the conrod not have an oil-hole? The .46Pro does and this gives you the clues as to orientation.

Why didn't you just scratch an X into the back of the conrod -- that's what I do, that won't come off :=)

XJet,
The original poster lost his mark and didn't know the correct orientation.
Marking the con rod IS the easiest way to determine orientation! But without the mark...
How does a hole in the 'big end' of the con rod help with front or back - just curious?

The side of the hole in the big end of the rod that goes towards the crankshaft has a bevel in the beginning of the hole. The other side, the hole is straight with no bevel.

The oil hole is centered on the bottom of the rod.

Its never a good idea scratch a mark into a connecting rod. Your setting up a stress point that eventually can lead to a fatigue point and rod failure. I had a brass wire around the rod marking the forward location, but when I went to remove the piston/rod assy from the anti-freeze bath it hooked on the case for an OS .10 FSR and that was all it needed to pull the brass wire off [>:].

Hogflyer

I'll have to pull it apart again, but it might be worth it to look for this. I used a magnafying glass to verify the wear marks on the rod where it appeared the front of the rod rubbed against the crank throw. Never thought about a bevel on the bushing to aid in getting it on the crank pin.

Since there was no forward/aft rocking of the rod on the crank pin I'm not as concerned about it wearing as I am piston/sleeve wear if the piston is rotated 180 deg from where is used to be.

Hogflyer

I don't know about any beveling on an oil/lubrication hole but the bronze bushing that is inside the conrod that fits over the crank pin should have a bevel on the side facing the crank. Just like w8ye said. (I'm guessing that is what Xjet was trying to say - sorry man.)

Hogflyer, if you are worried or think a little scratch or nick in the connecting rod will eventually lead to failure why did you take it apart? If you let it touch anything but silk a mark will be left on it!
That is a good one![sm=lol.gif] I have gouges in one of mine from a pair of Klein Needlenose plyers! (Don't ask![&:])
Shoot, some people drill lightening holes in their con rods!

Basically, look for the bevel in the bronze bushing, wear/swirl marks from the crank or backplate, carbon residue on the piston from the exhaust gases, wear marks on both piston and liner which match, and the extra play on one side of the wrist pin. Finding one or more of these (providing one suports the other!) will put you right on course!

The bevel in the bushing is not primarily for getting the rod onto the crank pin.

The bevel's primary function is to clear the fillet (Radius) between the crank pin and the counter weight on the crankshaft.

Here's what they're talking about. If you take off the backplate then the bush should look like the one on the right.

I believe it was GMS (?), who used (?) a crankshaft with the crank-pin pressed into the crank-web...

Such an arrangement tends to fall apart, but it does not have the radius where the crank-pin 'sprouts', so a symmetrical rod bottom-end is used...

I tore the engine down after work to look at the bottom end bushing. It does have the bevel on the bushing like picture from downunder shows, and it appears I did have it installed correctly. Since I never took the rod off the piston I'm now certain I have it with the correct orientation.

Thanks for the help everybody - this is what makes RCU such a valuable resource.

Hogflyer