| Author |
Message |
    
Tom Hare
New member
Username: hareball
Post Number: 1
Registered: 04-2008
| | Posted on Tuesday, April 22, 2008 - 09:18 pm: | 
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I was given a 60 hp from my brother in law and the upper cylinder was ruined. I hunted and found a real good motor that had an excellent powerhead (150 psi compression) It did have a bad stator so I installed that power head with my stator and rebuilt carbs (upper one re-jetted according to manual .0785) After running it a couple different times the new upper cylinder started showing signs of detonatin (aluminum deposits shorting upper plug). Thankfully it hasn't destroyed the cylinder. I had a mercury mechanic set the timing and carbs but he seemed to feel thay I had to large a prop stating if I wasn't reaching the correct RPM's the detonation could happen. It did have a 14 pitch prop and though the 16' boat seemed to run great I didn't have a tach. I went to a 13 pitch and put a tach in so I could monitor and I'm still a little shy of the recommended 5300-5500. Boat runs great but the detonation continued and he told me once they start they jusy get worse no matter how perfect everything is set up. I've pulled the motor apart to put as new piston and some rings in but do not understand why only the top cylinder did this. Can anyone help? Also I have two great pistons from the other powerhead (all standard) and I'm wondering if I'll be safe using one instead of buying new. Basically there was three common denominators between the motors, the prop, the stator, and the carbs. I have 35 years as a truck and auto mechanic so I'm pretty sure the rebuilt carbs are good. |
'Bandit
Advanced Member
Username: timebandit
Post Number: 274
Registered: 09-2007
| | Posted on Tuesday, April 22, 2008 - 11:29 pm: |
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 Throw the switch box away. Once the stator hi-speed goes the box goes. Those get replaced as a set. Find a new merc mechanic. That is 101 on these. The box will advance one cylinder until it blows. The bias cap goes bad inside for that cylinder. Every dang one of these. Thay had a bad rep for it in those years. |
Tom Hare
New member
Username: hareball
Post Number: 2
Registered: 04-2008
| | Posted on Saturday, April 26, 2008 - 04:51 pm: |
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Thanks for the info, that makes good sense with jut one cylinder acting up. What does anyone think about re-using a piston? I think it should be fine but I just don't have the outboard experiences to know for sure. I'm going to put new rings and main bearings also. |
Graham Lamb
Senior Member
Username: galamb
Post Number: 3050
Registered: 05-2007
| | Posted on Saturday, April 26, 2008 - 05:17 pm: |
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Tom, if it's in good shape just clean it up and should work fine for you... |
Tom Hare
New member
Username: hareball
Post Number: 3
Registered: 04-2008
| | Posted on Saturday, May 10, 2008 - 10:47 pm: |
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Sorry it took so long to get back, Thanks for all the info, I'm waiting on parts and should have it back together in a couple weeks. I've decided to get rid of the stator, switch box and due to bare wires, the trigger switch. I will adjust timing according to the specs in my manual and it should be great. |
ikia
Visitor
| | Posted on Sunday, May 11, 2008 - 05:10 am: |
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You have done the waterpump and cooling system maintenance??? Poppit valve has been looked at?? Thermostat ???? |
'Bandit
Advanced Member
Username: timebandit
Post Number: 329
Registered: 09-2007
| | Posted on Tuesday, May 13, 2008 - 09:33 pm: |
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Over-propping does not help, but if you lost a piston in a a few hours, than the ign is bad. |
carl spillman
Advanced Member
Username: papyson
Post Number: 154
Registered: 09-2006
| | Posted on Wednesday, May 14, 2008 - 06:45 pm: |
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Tom..(my apology to Graham and Bandit for jumping in)...i would not spend a lot of money on an older 3 cylinder merc..to me they are among the worse motors ever foisted upon mankind..in my opinion you can get those motors in new condition and it just depends on how many hours you run per year as to when you are going to drop that top piston..respectfully...Carl |
carl spillman
Advanced Member
Username: papyson
Post Number: 155
Registered: 09-2006
| | Posted on Wednesday, May 14, 2008 - 06:53 pm: |
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http://www.streetrodstuff.com/Articles/Engine/Detonation/Page_2.php |
carl spillman
Advanced Member
Username: papyson
Post Number: 156
Registered: 09-2006
| | Posted on Wednesday, May 14, 2008 - 06:55 pm: |
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if anyone has a better writeup on 2 cycle i would appreciate posting site...ty...Carl |
