Motor Tear Down

In the fall of 2010 I pulled the complete drive train out of my GMC Motorhome and replaced it with a remanufactured engine and transmission. The final drive was replaced in 2001 with a 3.42 from Cinnabar so I didn't replace that component of the drive train.

I decided to do a preemptive replacement for the following reasons:

In the November of 2009, while on my way to a camping trip, the engine started to make a "clicking/knocking sound".

	The sound didn't go away when I pulled the plug wires one at a time with the engine running.
	The motor seemed OK, except for the "clicking/knocking sound"

For the past couple thousand miles or so, the motor was consuming coolant. About a quart every five hundred miles. Nothing showed on the dip stick and oil levels seemed to be consistent with normal (for this motor) oil consumption. .

There were over 175,000 miles on the engine. As far as I knew, it had never had the valves done and I thought I had fairly complete records of all maintenance from the original owner.

However there was a receipt that showed that on 8-Aug-95 114,704 miles "Cylinder Head and Left exhaust Manifold resurfaced" Don's Quality Service, Flint, MI $602.37.

I don't think the valves were ground during that since it was described as "resurfaced".

I bought the coach 3 years and 8,000 miles later.

The records and my experience show extensive exhaust manifold work over the previous 35 years of service of that particular 455.

I had never replaced the transmission fluid since I bought the coach in 1998.

Oil pressure seemed low, but it always seemed low. When warmed up, at 60 miles an hour, it would run around 25-30 PSI at about 2500 RPM.

Sure I could have done a compression test, pulled the heads for a valve job and possibly replaced a bent or collapsed lifter. Rather than doing that, I decided that the time I spent doing that work, only to find out I had bigger problems, would be better spent replacing everything.

Here's a link to an album of pictures I took of a partial tear down of the old Oldsmobile 455 engine.

Motor Tear Down Photo Album

After posting these photos, I received an email from someone that knows a more about engines than I do:

If you want to feel real good about your decision to pull the engine, take just a few minutes to look at the pictures you took:

DSCN9289 - That corrosion on the top of the bore only happens went coolant leaks into the combustion camber after shutdown. The liquid coolant corrodes the piston rings - too. That both increases blow-by and allows more coolant into the crankcase and lube oil. At the very top of the frame, you can see where the combustion seal of the gasket has been breached. There are ring travel marks that should not be visible and the hone structure (required to carry lube oil for the piston rings) is gone from the top inch of the bore.

DSCN9299 & 9310 - The combustion seal of the aftermarket gasket has been leaking here too.

Yes, a valve job would have been a waste of money and everything else.

It only takes about 0.5% glycol in coolant to screw up the lubricity of the lube oil, and just a little above that it starts to attack the bearing materials. (I would bet money you were there.) The water in the coolant also loads up the oil drying capability of the system - hence the large amount of oil water condensate (brown goo) in the valve gear covers. This will also cause condensate to foul the intake air filter.

I can't give you an honest estimate of how long this motor had to live, but my guess would be less than 50 hours to a critical failure.

By the by, something had to cause that lash adjuster (lifter) to fail.

The upper piston (the thing that is cocked) is supposed to be a very close fit to the inside bore of the lash adjuster. If the lube oil is broken down, things like that fail real fast.

Matt

It would appear that I made the right choice to replace the motor in my GMC Motorhome.

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Page was last modified: 03/16/2011 10:20:30 AM