V-Twin Forum banner

1 - 11 of 11 Posts

·
Registered
Joined
·
1 Posts
Discussion Starter #1
Yesterday a customer brings us a 2001 Deuce. It's an 88 that's been 95'ed about 7000 miles ago. He says it has ran perfect until the other day. He had been out riding, brings it home and parks it in his garage. A few days later he gets on it, starts it and immediately it starts knocking. We start it up and yep, it's knocking and I mean loud. It almost sounds as if there is a gremlin in the crankcase banging on it with a big hammer. Immediately we say "rod". We start tearing it down and the first thing we find we have never seen before (and we have been in a whole bunch of engines during the past 25 years). Both pistons and cylinder walls have galling but only on one side of the piston. The other side of each piston and cylinder wall looks brand new. OK, I know this isn't causing the horrendous knock but this was the first odd thing we saw. As to the knock... we assume wrist pin or rod bearing but both seem to be working perfectly.
First question, any ideas what would have caused the galling just on one side of each piston and cylinder wall? Second, what's your ideas on the knock?
263775
263776
263777
263778
 

·
Make me use my bullet?
Joined
·
12,768 Posts
Were the galled sides both on the "inside" or "outside" of the cylinders relative to the crank? It has the appearance of a mismatched piston/rod combination.
 

·
Registered
Joined
·
8,446 Posts
there are little chunks of piston missing I'm the oil ring bottom land,,,
was the falling on the exhaust valve side, intake valve sides or?
 

·
Super Moderator
Joined
·
19,565 Posts
The galling is a heat issue.

In this case it looks to be from friction. What kind of oil pressure readings did you get before you tore it down? Past that plate the jugs up and see what sort of shape they are in. Make sure they didn't go out of round and pinch the piston skirts.

If I was a betting man, I'd put my money on something in the oil pump/cam chest. Perhaps even the oil pan gasket since its been worked on before.
 

·
Registered
Joined
·
5,089 Posts
This is a common failure, albeit not good. Sometimes the progression of events is that the tensioners fail and that crud gets into the oil stream. The tensioners get fixed and the bike is put back in service. Piston jets get clogged but there are also other items that can be affected.

The pistons did not seize. Seizing would present with bad skirts on both sides. The first event was likely sticking rods causing high thrust on the piston skirt and metal removal. The rings no longer turn and become microwelded in place. When they are affected only on the thrust side, which is likely how this presented, there are usually bad rod bearing(s). I replace them flywheels with an S&S replacement and for the same cost the motor can become a 103".

To fix this properly takes a full overhaul and cleaning of all the oil system including the oil tank. Once repaired it should be properly tuned. Measure the thickness of the piston skirts with a mike or caliper and report back please.
 

Attachments

·
Registered
Joined
·
5,089 Posts
Don,

I'm having a failure to comprehend moment based on the picture you attached. Can you walk me through why the thrust is indicated on the rearward face and not the frontward face? I'm just not getting how the forces are applied this morning.
Greg
It is a little hard for me to articulate but due to the rotation all rear sides, away from the direction of rotation, are the major thrust sides in IC engines. This is not unique to the Vtwin. If there are offset pins they are also moved toward the major thrust side. When a rod sticks these sides get hammered. I have some other thoughts about this issue regarding thin low tension rings but I don't want to add noise to the discussion. We can discuss this elsewhere if interested. Rings are the conduit for heat release, so that is a start.
 

·
Registered
Joined
·
5,089 Posts
That's probably enough for me to look it up now.
Think of the rod only supporting the piston evenly at TDC. After that pressure from combustion evenly on the dome push down but also cause the piston to rock because the rod is no longer directly under supporting the pivoting axes.
 
1 - 11 of 11 Posts
Top