Bad engine knock

[musselman]

I recently developed a bad knock in the engine. It's at the point now where I can almost hear it over the exhaust. Here is a video of it running, do you think it may be the lower rod bearing? It has the original crank in it still and the top end only has about 10 hrs on it.

 

[Braaaptor]

Yup, sounds like a crank (rod) bearing to me. Piston slap 'knocking' comes and goes as the engine is revved and decelerates. A rod bearing will knock more consistently, and seeing as how loud your engine has gotten...

I'd pull the top end and check it out. Any up-and-down play in the bottom end of rod, where it rides on the crankshaft, is a sign of a bad bearing. The rod should only slide side-to-side on the crankpin a few thousandths of an inch. Any more play, and its time for a new or rebuilt crank. Don't ignore this problem too long, or you risk the bearing failing and a possible broken rod. $$$$

 

[sicivicdude]

oh my... :-( that sounds horrible.

You're going to need to take that apart and find out what's causing that before it blows apart and takes out other parts.

 

[musselman]

Yah it's pretty bad, it all started after my engine took a gulp of water and mud thanks to my k&n filter.

 

[Braaaptor]

Yah it's pretty bad, it all started after my engine took a gulp of water and mud thanks to my k&n filter.

Did the engine hydro-lock while running? Ugh, if this happened, you may actually have a bent rod. Even if the rod is OK, your running engine having come to a sudden stop is more than enough to damage a Big End bearing.

 

[sicivicdude]

ouch. It sounds like it's time for crank/crank bearings. Either way the engine has to come apart.

 

[Whitty21]

Yah it's pretty bad, it all started after my engine took a gulp of water and mud thanks to my k&n filter.

ouch, water + engine = death, dont be surprised if ehat u find is ugly, that is a terrible noise though

 

[musselman]

It didn't hydrolock, there wasn't that much water but the problem was the mud along with it.

 

[musselman]

Thanks guys, I just wanted to have an idea of what might be wrong be I start tearing it down.

 

[Braaaptor]

No problem! Just start with removing the top end and piston from the rod, and go from there...

 

[musselman]

This should be interesting I think, it's the first time i'm going deeper than the top end.

 

[roadkill]

before you do that see if the head is sealing good cuz thats exactly what mine sounded like when it came wicked loose and didnt seal right

 

[Blasterdude27]

Well the good news is now its time for a stroker to go with that big bore

 

[musselman]

before you do that see if the head is sealing good cuz thats exactly what mine sounded like when it came wicked loose and didnt seal right

I'll definitely check that out but I think it may be a rod bearing just because it still has good compression and power.

Well the good news is now its time for a stroker to go with that big bore

Now that's what i'm thinkingI:I

 

[blasterfreek30]

damn man that sounds real bad...let us know what u find

 

[musselman]

Well it's been a while since I tore my engine down but I found that the crank bearings and both rod bearings were in great shape and within tolerance. I purchased a micrometer and measured the piston and got an average reading of 2.8305" but just have a cheap inside caliper so I don't know if the cylinder measurement is correct. I got the cylinder to be 2.8359".

These numbers indicate way too much piston to cylinder clearance I believe but I'm not sure which item is worn more, piston or cylinder. There are no scratches or anything on the piston or cylinder so why would there be so much play after only 10 hours of riding? Would the slight amount of muddy water passing through cause this?

 

[sicivicdude]

"average" reading is unacceptable for piston diameter.

You have to measure the piston diameter 10mm up from the bottom of the skirt from front to back to get the proper size reading. 2.830" is 71.88mm which is obviously not correct considering the vito's kit starts off at 72mm unless the piston skirt is damaged (which I have seen before but it's very unlikely).

Inside caliper is fine as long as you are careful and take your time... Just measure the cylinder bore size in all of the different areas the service manual says and record the different readings. If your cylinder to piston clearance is more than about .0035" you need to bore it oversize. With the extra amount of heat that a BBK has to deal with, you don't need tolerances being loose in there...

 

[musselman]

Ok here are some more precise measurements:

Cylinder:
Inline with pin
Top : 2.8374
Mid : 2.8334
Bottom: 2.8377

90 to pin
Top : 2.8363
Mid : 2.8369
Bottom: 2.8372

Piston 10 mm from bottom of skirt

2.8311"

 

[sicivicdude]

2.831 is 71.90mm which is slightly undersized for the piston and the cylinder is worn beyond the proper cylinder to piston clearance.

If you've got .006" clearance it'll sound like the video while it's running.

It's time for an overbore!

 

[musselman]

I can't believe this, only 10 hours on this top end and it's done already. I only have 1 bore left after this time :S. Would ingesting a bit of water/mud cause the cylinder to wear that much?

I guess i'm going to put my stock jug back on for now.