Triumphrat

KitNYC

I would like to know why my motor seized, but I would like much more than that to have a running bike. Money is tight & I don't want to spend $200 for another month in the garage, so I'm trying to piece together what went wrong with the engine still on the bike. I have a few clues so far, & will post more as I find them....

1- 500 miles after I replaced the head gasket due to coolant leaking into the sump, the motor seized up tight. I was attempting to chase down what appeared to be high-RPM fuel starvation at the time. I redlined it for 2 or 3 miles, then as I was pulling off the highway it started making a funny noise around 3 or 4k. Another block & the oil light came on. 2 more blocks w/ the light on before I could get out of traffic. I let it rest & cool down, checked fluid levels (good), & got it started again. It idled with the oil light off, so I set out to limp down 6 miles of back roads to get home. Within 2 or 3 blocks, the motor stopped spinning.

2- The cam chain is still in place & under tension. When I pulled the motor apart, the arrows on the cam sprockets were both pointing a few degrees downward from directly at each other. I put it back the same way, after noting that that was as close as possible to having the arrows point at each other.

3- The motor is stuck with the timing rotor on the T2 mark.

4- I put Shell Rotella oil in for the first 100 miles, to sort of rinse out whatever was left of the oil/coolant mix from before. It came out looking just as dirty as my last 6k oil. I then put in my usual Mobil-1 15W50. When I drained that after the lockup, it was also filthy. Black as night with bits of black stuff in it. There were no metal bits in the oil, but there were a fair number of what I can only describe as carbon flakes.

Is that enough info for anyone to make an educated guess as to what happened?

Thanks,
-Kit

Major Kong

Hi Kit,
I didn't know about you draining the crank and finding debris in the oil. Maybe some of the RTV or gasket agent came off at high rpm and either fell on the cylinder wall or broke off at the base and cloged an oil journal, wiping the crank?

You probably need to pull the head and, or oil pan off to know for sure.

Zip

__________________
"Only by challenging and questioning our beliefs can we come to the point of ownership of those beliefs."

KitNYC

Yeah, I only drained the oil a few days ago & this was my first chance to post about it. I wonder where gasket agent would have come from? I guess I will start pulling it apart as time allows; not like I'm worried about street grit getting into the motor anymore...

Cheers,
-Kit

alfacliff

bits of black stuff sounds like possibly your chain tensioner came apart. had trouble with them on the old xs650's, first plastic bits then a lot of aluminum powder.
cliff

__________________
2006 Bonnie Black
1980 Yamaha xs650 sold 4-30-2011

kludge

I think that is the most telling statement in your whole series of events. You were running the motor at high revs. Then there was noise. Then the oil light came on. Basically, if the oil light is on at any time other during cranking, you have done damage.
My guess is that while running at high revs you might have pulled some crud from the previous blown gasket incident into the oil pump. Maybe it blocked an oil way or damaged the pump. You say the oil was filthy and black, so perhaps that crud had opened the oil filter bypass valve. You either seized or spun a rod bearing or a main bearing.
As long as there is even a little oil splashing around in the motor the pistons will not seize. Plain metal bearings die a quick and horrible death as soon as pressure drops too low to maintain that hydrodynamic wedge.

__________________
My other ride is 28m2 of nylon

KitNYC

Alfacliff: I don't think it was the tensioner; I did not see any evidence of debris around the cam chain tunnel. Here's a pic inside the timing cover after the incident:



Kludge: I think yours is the most plausible theory yet. Hopefully, I'll be able to take the motor apart & figure it out.

Thanks,
-Kit

Pablo

Typically if a four stroke engine looses oil pressure after a hard run it is a spun bearing. If it locked up solid like that I would guess a main bearing. Looks like you need to pull the bottom end apart.

KitNYC

Thanks, Pablo. Love your STSS, BTW.

Cheers,
-Kit