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1985 35HP Mercury need to change reed valves.

D

dolfan13

New member
I need to change the reed valves. The mechanic I took the boat to says it is too much cost in labor for him to do it. Trying ourselves. How do I get to the valves. Stuck at how to get to the crankshaft. The reed valves for this model are in the crankshaft

Thanks
 
What exactly is happening with your motor Reed valves seldom go bad. But if you do need to replace them you need to pull the powerhead off of the motor. Then split the crakcase and the valves will be there. Get a Good manual for your motor.
 
flyingscott said:
What exactly is happening with your motor Reed valves seldom go bad. But if you do need to replace them you need to pull the powerhead off of the motor. Then split the crakcase and the valves will be there. Get a Good manual for your motor.
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Engine will not idle or maintain power. The diagnosis came from the mechanic we took it to. How do you split the crankcase? I have downloaded 2 online manuals at $30 each and both are useless. Thanks for any help.
 
Stop--------Do some trouble shooting.-----The reed valves rarely are the cause of this.-----Post the results of a compression test.----Check spark on BOTH leads.----Does it jump a gap of 3/8" or more , yes or no.-----No insult but if you have to ask how to get to the reed valves this project will take a long time.----What other trouble shooting has been done ?
 
racerone said:
Stop--------Do some trouble shooting.-----The reed valves rarely are the cause of this.-----Post the results of a compression test.----Check spark on BOTH leads.----Does it jump a gap of 3/8" or more , yes or no.-----No insult but if you have to ask how to get to the reed valves this project will take a long time.----What other trouble shooting has been done ?
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Our mechanic is the one who told us it was the reed valves and it would cost to much in labor for him to to the repair.
 
To replace reed valves on that motor you have to completely take the powerhead off of the motor. You then have to take the whole powerhead apart same as for a rebuild. You may want to listen to racer and do the simple tests on it. I agree with racer I do not believe the reedvalves are the cause of that.
 
Find another mechanic!

Lots of reasons why it won't idle: bad compression (do a test and find out), bad crankcase seals, carb messed up, etc. Note I did not include bad reeds--they rarely go bad on Mercs.

Jeff
 
dolfan13 said:
I need to change the reed valves. The mechanic I took the boat to says it is too much cost in labor for him to do it. Trying ourselves. How do I get to the valves. Stuck at how to get to the crankshaft. The reed valves for this model are in the crankshaft

Thanks
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Your mechanic is half right. The issue is your reed valve block is bad. This is the machined center portion of the reed block that is called the labyrith seal. It is where the center portion of the crankshaft rides on this aluminum "bearing"and has excessive clearance from crankshaft wobble. It was a major problem on all 402 version Mercs. Many of them actually broke the crankshaft if the engine was lugged and not propped correctly. What happens is when this seal is worn, the fuel charge and intake scavenging becomes interrupted from pulse leakage between the cylinders and the engine will not idle correctly, stalls and lacks power. The standard clearance was around .003" enough for oil film in the seal. I have seen one with .020" from wear but ran terribly. The only fix is to replace the reed block with a new one which are now NLA but can be found on ebay. Also you need to have crankshaft measured for straightness and see it it's bent. This was a common problem on this engine.
 
Interesting comment. For many years now I've run the early Merc triples, and I've only seen one that idles worth a damn. (All of mine won't hold an idle below 1,000 rpm in neutral, and I'm talking about a dozen plus.)

After thrashing away on this problem for years, my conclusion mirrors your excellent response: lousy inter-cylinder sealing.

Merc triples are unique in having all roller bearing/ ball bearing mains. They're also INFAMOUS for having a lousy idle that defies carb adjustments to cure. I'm of the belief that those roller bearing mains of theirs are the reason why: they're leaky as hell! Gas/ oil drips right through them, and air leaks back and forth (actually up and down) like crazy.

I know what you're thinking: The big in-line sixes also use two of these roller bearing mains, and they idle like a Rolls Royce. True, but (in addition to having double the cylinders firing) they also have three labyrinth sealed reed blocks that make many of their cylinders run nice and clean.

Jeff
 
Your close Jeff......its the reed block itself, the flat reeds sucks. If it had reeds line a I6 it would idle. All I am going to say :cool: as and the OP's 35hp has reeds line the I6
 
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