Force 120 reed valve plate broken, where does it go?

[lucida]

Hi, need some advises please.
I have a 1996 sportjet 120 (Force 120 engine). Engine turn over but not start. Change spark plug, check the ignition, clean the carbs, check the fuel pump, check the compression....all no help. Engine just don't start. Decide to take further parts out and found this:

upper reed plate:

lower reed plate:

Can not find where the broken reed plates go??
Question:
Do those broken reed plate inside the engine will make more damage?
Any idea how to take them out?

Thanks.

Joe

 

[Frank Acampora]

Re: Force 120 reed valve plate broken, where does it go?

Those are called reed petals and they usually pass right through the engine when they break. Sometimes they will damage the top of the piston and the head, sometimes they will not, but that will usually not affect running.

You need to either go to your local Mercury dealer and buy replacement reeds--UGH! Very expensive--, Buy a used set on ebay, Buy Boyeson reeds or other high performance reeds, or sustitute in a set of Vee blocks and reeds form an older Chrysler engine--they last longer.

Boyeson reeds are plastic and if they fail, absolutely no damage will be done to the engine, buty they do cost around 125 bucks.

 

[jason32038]

Re: Force 120 reed valve plate broken, where does it go?

http://outboardparts.com/chrysler/mall/reeds.htm

 

[lucida]

Re: Force 120 reed valve plate broken, where does it go?

Thanks for replying.
A quick update. I bought 2 old complete reeds assembly, not sure what year is that, but it has 5 patels instead of 4. Put them on, no need to modify, even the gasket is the same.
Test it in the lake today, engine ran better than before. RPM easily reach to 6000 (rpm limit, the yellow/black wire, has been disconnected), stable idel, throuttle response very fast.
Ran for 1 hours without any problem. Still don't get it where does the broken petals go?

 

[Frank Acampora]

Re: Force 120 reed valve plate broken, where does it go?

Reeds are one way valves to allow alternate suction and compression inside the engine crankcase. They stop the fuel/air mixture from blowing back out the carb when the piston travels down, compressing the air inside the crankcase.

Stock reed petals are very hard spring steel. When one breaks, the petal or its parts travel directly into the engine crankcase with the fuel/air mix where it is mashed around by the crankshaft, connecting rod, and piston. It may break some more or may not. It then blows through the bypass ports into the combustion chamber where it may hit the top of the piston and cylinder head leaving some sharp dents, before it blows out the exhaust ports and down the leg into the water. So, it is rare to actually find a broken reed petal inside the engine.

Because the total reed area when all are open at speed is much greater than the area of the broken petal, if only one reed petal breaks, the engine will have some crankcase compression and will continue to run, but at reduced power. It may even restart after being stopped, but with much difficulty because at low cranking speeds, the reeds don't open very much and the broken area is greater in relation to the total opening, allowing escape of most of the air/fuel mix.

 

[mrdibs1]

Re: Force 120 reed valve plate broken, where does it go?

Will compression be normal with a broken reed plate? I have symptoms that appear similar, but mechanic blaming carbs. They were very clean so I'm skeptical.

 

[RRitt]

Re: Force 120 reed valve plate broken, where does it go?

Will compression be normal with a broken reed plate? I have symptoms that appear similar, but mechanic blaming carbs. They were very clean so I'm skeptical.

When mercury took over production they upgraded Force engines with some nifty self-destruct mechanisms including the reed valves, fly-apart stators, and crumbly trim seals. The generous half of me says that it is because they were trying to improve performance or some other reason. The cynic in me says that they wanted to make sure Force engines did not outlast Mercury or Mariner labels. In reality I think they were just being cheap and did not care what happened after warranty ran out.

At any rate, broken reeds aren't very common before serial # 0E009500 (1992ish). Those engines were still mostly Chrysler.