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morisani
Italy
109 Posts |
 Posted - 28/05/2008 : 11:44:58
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After running up and down hills for many miles the engine of a PA started going on with only three cylinders (one - the third - not working). Spark-plugs, carburetters, water and oil all ok. Opened the cylinder head cover assembly I noticed one of the Crankshaft brass totally worn out; it is the rear one. One another is partially worn out. The oil pipes are perfectly clean.
Any advice about the orign of the brass worning out?
Thanks in advance, ciao
Francesco (Italia) |
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Gerhard Maier
Germany
873 Posts |
Posted - 28/05/2008 : 13:43:04
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Francesco,
do you speak about the white-metal in the camshaft bearings ? |
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kimber
United Kingdom
1529 Posts |
Posted - 28/05/2008 : 19:12:16
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| Or, do you mean rocker bush? If so, that sounds like an oil feed issue which can easily happen for various reasons which I will happily explain if, indeed, we are talking about the same thing! |
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morisani
Italy
109 Posts |
Posted - 29/05/2008 : 10:22:21
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Sorry for my English. The right definition of the worn out part must be camshaft bearing.
Thanks
Francesco |
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rbm
United Kingdom
141 Posts |
Posted - 29/05/2008 : 16:48:19
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Hi Francesco,
has the bearing worn out or has it melted?
I had the rear one on my M melt and whilst stripping the top end, found that the oilway drillings in the rear cam support were incorrectly machined from new one side feed was not drilled through at all, and the other blocked.
Richard |
Edited by - rbm on 29/05/2008 16:56:42 |
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Gerhard Maier
Germany
873 Posts |
Posted - 30/05/2008 : 19:17:15
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Francesco,
there are many reasons which can lead to a camshaft-bearing problem.
It is unusual that the camshaft bearings are ôbrassö and not white metal, but I have seen that before, and it should work when a bearing-bronze was used.
Did you care that the camshaft stands were in line ?
Was the camshaft straight, and the bearing shells the right size?
Was your engine oil pressure OK ? (always between 40 to 80 pounds)
Is your cyl.-head restrictor pin + the bore original size ?
Sometimes the oil ways in the camshaft stands are blocked by 70 year old deposit ?
Have your rocker-shafts the drillings in the right positions ?
And are they fitted each to the correct side + not turned 180? by mistake?
The intermediate and rear castings of the camshaft stands have 3 holes on the surface where the white metal bearing shells should be positioned.
The bigger hole in the center is a blind hole for the fixing pin of the bearing shell.
The small hole in same line, is the feed drilling where the oil, which is delivered from both the rocker shafts, should enter the bearing.
The 3rd hole, slightly offset, is another drilling all through the casting into the open.
(has somebody a idea for the existence of that 3rd hole? perhaps more oilflow for cooling?)
But caution, if the bottom half of the bearing shell is wrongly fitted front to rear, both those drillings could be blocked with expensive results.
In my opinion, assembling the MMM cyl.-head is quite a challenge!
Gerhard
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morisani
Italy
109 Posts |
Posted - 03/06/2008 : 14:54:12
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Thanks a lot. I've to study carefully the situation (and the answer) and need some time to do.
Ciao
Francesco |
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