Weird 454 rapping
04-06-2006, 09:56 PM
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Weird 454 rapping I'm a new user of this site, and hope that some members may give me the benefit of their experience. After years of mainly operating Cat and Detroit diesel powered machines, I now own two pieces with GM 454's.
The K-30 454 is a fine engine, except that once while towing a 42,000 Lbs trailer (38' navy surplus landing craft) up a long hill it overheated. Did fine coming down, though.
But then there's the Land Sloth, my motor home, a 1990 P-30 conversion, typical TBI unit.
Driving down the road, slow and easy, it started rapping. Sounds like a loud tappet, but isn't. Have removed both heads, and there's nothing loose in the combustion chambers. It's not the flex plate. I don't think it's the fan or balancer. What does that leave.
Engine has plenty of oil pressure at start, idle, and running temp. Plenty of power. It has an faintly audible tick at idle that increases to a rap under power.
I've dropped the pan, and opened up the #2 con rod. Worn (105,000 miles) but not hammered flat. Oil analysis shows pretty high copper, lead, and iron, which suggests bearing problems.
Now what? Replace the rod big end bearings?
Anyone know what a bearing shell number like this means? GM4 2643131
It's all a mystery to me.
Thanks in advance for any advice.
seo
The K-30 454 is a fine engine, except that once while towing a 42,000 Lbs trailer (38' navy surplus landing craft) up a long hill it overheated. Did fine coming down, though.
But then there's the Land Sloth, my motor home, a 1990 P-30 conversion, typical TBI unit.
Driving down the road, slow and easy, it started rapping. Sounds like a loud tappet, but isn't. Have removed both heads, and there's nothing loose in the combustion chambers. It's not the flex plate. I don't think it's the fan or balancer. What does that leave.
Engine has plenty of oil pressure at start, idle, and running temp. Plenty of power. It has an faintly audible tick at idle that increases to a rap under power.
I've dropped the pan, and opened up the #2 con rod. Worn (105,000 miles) but not hammered flat. Oil analysis shows pretty high copper, lead, and iron, which suggests bearing problems.
Now what? Replace the rod big end bearings?
Anyone know what a bearing shell number like this means? GM4 2643131
It's all a mystery to me.
Thanks in advance for any advice.
seo
04-07-2006, 06:34 AM
#2
Eh, I wouldn't worry as much about the bearing number as I would clearances. Bearing technology has come along way in the last 15 years. Obviously the motor is out of the RV. I'd tear it all down and have it checked. You can probiably get away with just honing it, putting in new rings, new cam bearings, timing chain, oil pump, have the crank polished, grind the valves, grind the seats, install new valve seals, new guides if needed, and springs and install new bearings all the way through. Might not even need half the stuff I mentioned or maybe will need alittle more you'd have to see when you got it apart. Being it hasn't self destructed you can probiably get out of this with a reasonably fresh motor for under 1k in parts. Sounds to me like you have a rod knock. I'd be willing to bet one of your bearings is trashed. Not sure what the main and rod journal sizes are but as a general rule of thumb, you should have about .001 of clearance per inch of journal diameter but obviously you have to check the manual.
