Engine rattle at WOT - Found a Bolt

[Mike Orth]

I am running a 1996 125 Carb on my Nitro 176 and I heard a short rattle when I got up to WOT on my way back to the ramp. When I heard the rattle I backed of the trottle, crusied at about 4,500 rpm for a few seconds, then throttled back up to WOT. The rattle came back. I got a bit nervous,:unsure: so I slowed and trimmed down. Rattle went away. I then made a large turn and put the hammer back down bringing the engine back up to WOT. Never heard the sound again. I ran back to the ramp at WOT for about 60 seconds and all seemed ok.



My prop is not loose, it spins with out wobble, and the sound seemed to be comming from unber the cowling. No rattle at low and mid range rpm.



Any thoughts on what that rattle may have been. Rev limitter?



Worried I might be loosing a cylindar!



Mike



Nothin' Beats a Black N' Blue Jig!!

 

[Bob Bourget2]

Rattle or squeal? Just curious.....

 

[Mike Orth]

Hey Bob, It is a rattle. Like a really fast clicking.



Mike



Nothing Beats a Black N' Blue Jig

 

[Todd Bennett]

My guess is you are getting a little detonation or pinging! You might have gotten some bad gas, fill her up with premium I bet the rattle goes away.

 

[Bob Bourget2]

Pull the cowl off next time your out using it, and have someone drive the boat while you "observe". Watch the starter drive closely and see if it is "jumping around". They tend to rattle significantly when "aged".....especially as "harmonics" tend to come together...... Check all fasteners and cowling attachments.

 

[Mike Orth]

I always burn Non-Oxy so I do no think it is fuel related. Bob, I will pull the cowling next time and give her a listen thanks for the tips and I will post with my leanings.



Thanks guys for your responses.

 

[Mike Orth]

Bob B. and members,



I was able to run around the lake this morning with the cowling off and did not hear anything other than a well tuned 125!! However, I did find the source of the rattle. A bolt in laying loose in the base/pan of the power head.



This could be a bolt that got dropped prior to me owning it (I have owned it for 1-year), or could it be something that vibrated loose? I can not find an open threaded hole that seems to be its home.



The bolt in question is photoed below. It is either and 8mm or 5/16 - 1 1/4 inch. Tried to get the thread, but do not have a gauge. I know that it did not thread on to a 10-24 nut...



Any ideas on where this may be from? Hoping Bob B. has a resource to ID this bolt size and it possible uses on my engine.



1996 Merc/Tracker 125

Serial #OG387689



Mike