| [GMCnet] More water pump thoughts/observations [message #179838] |
Sat, 11 August 2012 11:46  |
Jim Miller
Messages: 501
Registered: March 2008
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A couple thoughts and observations related to water pump / temperature control issues.
1) Not too long ago Dick Paterson related to me a story about an engine he worked on that had overheating problems under certain operating regimens. After checking all the usual causes of overheating - timing, thermostat, radiator condition, fan clutch, coolant flow, etc. he could not find the problem. Finally, he decided to change the water pump - and found that the old water pump's impeller was not firmly attached to the driving shaft. It would work properly at low RPM and flows but it would slip on the shaft under load.
2) I fought overheating problems for two years in my 455 with 50000 miles. Checked all the usual and not-so-usual stuff but could not find the problem. This year I started the coach for the first time of the season and discovered raw coolant coming out of the left-bank exhaust. Turns out that the left head had a crack between the valves in cyl #1. The walls of #7 also had evidence of coolant incursion from an unknown source.
Here's the water pump tie in.... while reassembling the engine I was installing Mondello's valve-lifter cover. In the process I managed to drop one of the 1/4-20x3/8" bolts down beside the cam and into the oil pan. I could not fish it out with a magnet so I decided to take the timing cover off and fish from the front. In order to save reassembly time I removed the cover with the water pump still attached to it. Once I had the assembly off the engine I discovered that the hole in the driver's side of the timing cover did not properly line up with the matching passage in the water pump. This misalignment caused perhaps 20-30% of the path to be blocked. I resolved the issue by using a carbide burr to port the water pump casting.
Those of you who have your timing cover off the engine for whatever reason might want to check the water pump / timing-cover fit-up.
--Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] More water pump thoughts/observations [message #179858 is a reply to message #179854] |
Sat, 11 August 2012 13:57  |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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On Aug 11, 2012, at 2:41 PM, Ken Burton wrote:
> That is not something one would normally think to check.
Hi Ken,
No kidding. If it hadn't been for that dropped bolt I never would have found it.
I suspect my engine may not the only one with the coolant passage fit-up problem. I say this because in the process of repairing my engine I bought two sets of "J" heads - one set from Ebay and one set off of Craigslist. Both sets were from non-RV 455 engines. When I cleaned them up and dye checked them I found that one head out of each set had cracks identical to mine!
Out of a sample set of three pairs of heads acquired essentially at random, all three of them having identical failures seems like something more than coincidence.
73, Jim N8ECI
--
1977 Eleganza II
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] More water pump thoughts/observations [message #179946 is a reply to message #179838] |
Sun, 12 August 2012 10:53 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
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Jim,
Thanks, I wrote down a mental note to check this.
Regards,
Rob M.
-----Original Message-----
From: Jim Miller
Those of you who have your timing cover off the engine for whatever reason might want to check the water pump / timing-cover fit-up.
--Jim
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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