jeffswav

I just installed a fresh engine in by boat. After about 2 hours of run time I hear what sounds like a rod knocking. After disassembly we found the top rod bearing caps on all cylnders to be down to the copper. My machinist speculates the cause to be "Bad Gas" or to much timing advance. I do not believe it to be the timing. Does anyone know how to get the octain checked I still have 40 gallons left the the tank? I filled the tank in November with 93 octain fuel with Stabilizer. I have done this every year and never had any problems. Since this happened I have done a lot of research on this and everthing I have read says it is only good for 30 days weather you use stabilizer or not. What is the real deal?
Engine specs:
489 stroker 9.3 to 1 compresion
Large Oval Cast Iron Heads
All forged parts

Thanks,
Jeff

Jerry B

I cant imagin bad fuel causing bearing failure. If the clearance was correct and you had proper oil pressure my guess is the block or something internal was not cleaned properly. We have had bearing failure after using the 3m scotch wheels on a grinder to clean surfaces. If any of the dust comes off and enters the oil it's curtains for bearings.
I know this doesnt answer your question on haveing fuel tested. I will ask one of the drivability techs in our shop about that. I know they have a test kit to check specific gravity but I dont know enough about it to say what it does. I think it may just check for alcohol but not octain.
One more thought. If the octain was way low and the engine was detonating badly it can and will cause a porblem but I think it would damage pistons first and you dont have much time on that rebuild.

Sorry to hear about your engine.

Jerry.

jeffswav

Thanks for the reply!
The pistons and cylnder walls were fine, the problem was with the upper half of the rod bearings. The page in the book showed a picture with a similar problem, with the top bearing (bearing closer to the piston), worn more than the bottom. The cause in the book was either bad fuel, to much timing advance. I monitored the O2 readings on my laptop and it never went lean.
In any case I have been doing business with this place for a long time and he is going to cover most everything under warranty. I just don't want to go through this again. Pulling engines takes away from boating.
Thanks,
Jeff

BillK

Jeff,
Detonation from any source will cause the bearing wear that you have. You mentioned that you have o2 sensors and a laptop. Is this an EFI system ? Any way to add a knock sensor to it that can be monitored ? That may tell you more than the o2 sensor. You can have detonation and not be lean.

jeffswav

Thanks for the reply:
I have a Holley MPI setup. There is an option for a knock sensor but I do not have one. I do not think you can monitor it but I do believe it would retard the timing. Do you think this would help?

Thanks,
Jeff

stevesxm

if it was bad gas/detonation enough to damage the bearings ( a 10,000 to 1 chance) you would be able to check simply by looking down thru the holes in all the pistons. they would give up LONG before you would see any shock load damage in the bearings.

jeffswav

Steve
That's what I thought. I have been working on engines for 20 years (as a hobby) and I did not hear any sign of spark knock. When I heard the noise I thought it was a rod bearing. But the damage was very strange, with the tops of the rod bearings being more damaged than the bottoms. And the mains had less wear than the rod bearings. Any thoughts from anyone would be appreciated.
If I had the timing advaced to far (which I don't think I did) would'nt this damage the pistons also?

Thanks,
Jeff

Griff

Stabil does nothing to retain octane. Octane depletes at about 1/2 a point per month. If you put 93 in in NOV, then its probably close to 87 now.

I still don't think this would have caused your problem though, unless you other obvious signs of detonation.

stevesxm

absolutely. detonation from any source sufficient to do any damage at all will show up on the plugs and pistons long before the shock loads are sufficient enough to damage the bearings...

based solely on what you describe , it really sounds like an oiling/ clearence issue to me... especially the fact that it was all the bearings... that smacks of some significant oiling issue...

as simple (as noted in these threads) as getting the oil lines backwards on the adapter to badly machined hard parts with the resulting tight ( or loose) clearences... only a careful forensic disassembly will tell you the answer

but i think it a zero chance it was fuel related unless you were fuel diluting the oil by being wildly rich somehow...

NJgr8ful

I just finished having 2 motors built, new heads, cams ... builder(s) told me to dump 200 gals of 93 octane (plus stabil) from last Oct 30 $600+ and 3-4hrs later after draining, dumping, and RE-fueling I'm running with the new motors on Sunoco 93 and keeping fingers crossed My builder said he will not warranty anything becasue of bad fuel from the winter/fall.