Mower locked up - final results

[GreeCguy]

Good morning fellow oilers:
Stayed up late last night taking apart my mower. I knew there was internal damage when I took the motor off the mower deck and could hear parts rattling around inside the motor. Sure enough, when I disassembled the motor, the plastic, (yep - plastic), oil slinger inside was broken into three pieces. This slinger is driven by riding a gear on the cam shaft. The gear teeth on the plastic oil slinger were very worn. It's my guess that the teeth finally wore down to the point they would not ride on the cam teeth and probably jammed into the metal teeth on the cam gear causing the slinger to break. With no slinger, no oil being slung. No slung oil, no cylinder/piston lubrication. The cylinder and piston have very deep scouring, (way past the point of being able to bore it out and rebuild it). However, the connecting rod and crankshaft seem to be in good shape. So if I ever need a rod or crankshaft for a Briggs and Straton 5.5 h.p. motor, I've got one - boy, just what I needed.

 

[doitmyself]

Internal plastic engine parts - go figure. My workplace has a John Deere 725 mower ($9,000) with the time honored Kawasaki liquid cooled engine. When the water pump went out, the JD mechanic asked if I wanted to have the camshaft replaced while he had the engine apart. I asked why? He said that JD speced a plastic camshaft to help quiet the engine. I had the mechnic install a new metal camshaft - at our expense for JD's engineering experiment.

 

[Neever]

Wow, how can one tell if their engine has plastic parts? Does anyone know of a website that lists engine drawings/parts?

 

[1 FMF]

had the exhaust valve seat let go in a 3.75hp b&s engine last summer. pulled all apart, real simple crankcase design. Plastic oil slinger like you said. Did you also notice the plastic cam lobes?
Remembering how the oil slinger fit in mine, I can sort of see how they can wear out. I suppose using a tough (polyimide?) plastic for the cam isn't a bad idea- a lot less weight with easier manufacture and less vibration is a good thing I guess. They had no visible wear in them from the flats of the valve pushrods. And that engine was rigged to run 4k rpms + instead of the governed 1700 or 2000.

 

[1 FMF]

forgot to mention, you can download briggs and straton manuals from their website and get part #'s. Should be able to view pics of the internals.
But you need the engine model # or serial # to access the manual, otherwise you're guessing and sifting through hundreds of different manuals.

http://www.briggsandstratton.com/display/router.asp?docid=78484

 

[Tremo]

They've been using plastic oil slingers in those small vertical shaft motors since at least the 70s.

I think my Tecumseh has a piston type oil pump, but it's probably plastic as well.

 

[Stoney57]

When I learned that the newer 3.5 hp briggs engines had plastic cams, I emailed briggs and asked how long it would last. Here is their response.

Response (MATTHEW) - 06/19/2002 03:19 PM
Thank you for contacting Briggs & Stratton E-Customer Support!

Your 3.5 hp engine has a plastic composite cam. With proper maintenance, the cam will outlast the engine. Our plastic composite parts have a higher tensile strength than steel, and have proven to be very reliable.

Customer (Jon Krull) - 06/18/2002 11:43 AM
Hey, I just bought a standard push mower with a briggs 3.5 hp motor. Date code says it was built in March of 2002. Does it have a plastic cam? How long can a plastic cam last anyways?


Question Reference #020618-000021

 

[Shannow]

quote:

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Originally posted by Stoney57:
Our plastic composite parts have a higher tensile strength than steel, and have proven to be very reliable.

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higher tensile strength than steeel ?

and besides, what does tensile strength have to do with the loads on cams ?

Even assuming the first statement was correct.