THUD sound when cruising

Author Message   larry bryce Member Username: larrybr45 Post Number: 6 Registered: 07-2007 Posted on Thursday, May 15, 2008 - 08:34 am:    I have 1978 35HP outboard When I cruise, regardless of speed, I heard a thud sound from the engine periodically, and the boat shakes a little. I dont loose any speed. Any thoughts on what this could be? What risks are there of not fixing? Is there rough idea of cost to repair/time involved? Thanks for help.   Morten Ringvold Senior Member Username: haffiman37 Post Number: 2731 Registered: 04-2006 Posted on Thursday, May 15, 2008 - 08:47 am:    Gear and clutch dog not properly engaged and 'slipping. Best case: adjust shift cable. Worst case: change clutch dog and forward gear.   larry bryce Member Username: larrybr45 Post Number: 7 Registered: 07-2007 Posted on Thursday, May 15, 2008 - 12:09 pm:    I am somewhat mechanically inclinded - Is there directions somewhere on how to adjust the shift cable? thanks!   Joe Reeves Senior Member Username: joereeves Post Number: 6021 Registered: 02-2001 Posted on Thursday, May 15, 2008 - 12:24 pm:    (Centering Shift Cable) (J. Reeves) When all is as it should be, the proper method to adjust the shift cable is to disconnect the cable from the engine. Move the shift linkage on the engine to find the center of the play in neutral, and when found, leave it centered. Now, grab the end of the shift cable sleeve, push and pull it to find the center of the play there, and center that play. Adjust the trunion on the threaded portion of the shift cable so that the centered play of the cable lines up with the centered play of the engine's shift linkage. Install and lock the shift cable with the retaining clamp in that position. That's it. When time permits, visit my store at: http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store (Jumping Out Of Gear - Manual Type) (J. Reeves) This pertains to lower units on all OMC manual shift outboard engines, or any OMC engine with lower units defined as a Shift Assist or a Hydro Electric Shift unit which incorporates a "Shifter Clutch Dog". Within the lower unit, splined to the prop shaft is what is most often referred to as a clutch dog, hereafter simply called dog. The dog has at least two lobes protruding from it on both ends, facing both forward and reverse gear. The forward and reverse gears also have lobes built into them near their center area. When the engine is running, in neutral, the gears are spinning constantly via the driveshaft being connected directly to the powerhead crankshaft, but the propeller does not turn due to the fact that the dog is centered between the two gears, and the dog lobes are not touching either of the gear lobes. When the unit is put into either gear, shift linkages force the dog (and its lobes of course) to engage the lobes of the gear. The lobes of the spinning gear grab the lobes of the dog, and since the dog is splined to the prop shaft, the propeller turns. The lobes of the dog and gears are precisely machined, most with right angled edges that could be installed in either direction, and some with angles slightly varied that must be installed in one direction only (one end only must face the propeller). Dogs that can be installed in one direction only, if reversed, even if the dog and both gears were new.... would jump out of gear almost immediately. Keep in mind that the lobes are precisely machined with sharp angles! Due to improper adjustment or worn shift linkages, but usually due to improper slow shifting, those precisely machined sharp edges of the lobes become slightly rounded. Now, with those lobes rounded, as the rpms increase, the pressure of the gear lobes upon the dog lobes increases to a point whereas they are forced apart (jumping out of gear), and due (usually) to the shift cable keeping tension on the engines shift linkages..... the unit is forced back into gear giving one the sensation that the engine has hit something, and the cycle continues. Some boaters have the mistaken belief that shifting slowly is taking ixt easy on all of the shifting components..... Wrong! Shifting slowly allows those precisely machined sharp edges of the dog and gears to click, clank, bang, slam against each other many times before they are finally forced into alignment with each other..... and this is what rounds those edges off! The proper way to shift is to snap the unit into gear as quickly as possible. When time permits, visit my store (copy/paste) at: http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store

Administration Log Out   Previous Page Next Page

Home / Directory | Engine Manuals | Engine Parts | Discussion Board | Free Classifieds | Orders / Shipping | Contact Us | View Cart

About Us | Terms of Use | Privacy Policy MarineEngine.com, 184 Jones Dr., Brandon, VT 05733 USA Phone: 802-247-4700 FAX: 802-301-1034 info@marineengine.com Copyright © 2000 - 2007 by MarineEngine.com, Inc. All rights reserved

Traduca Traduisez Traduza Traduca Ubersetzen