motor thumps

[noah4009]

I have a 1971 55HP Chrysler. Model 557HC serial 3188. Thanks to you guys I have the LU on sealed and with a new impeller. My new problem is. I just started it and the water cirulates fine. But while running about every 4 seconds or so the motor will knock. I sounds like a metal knock. The motor will rock each time it knocks. run smooth then thump then smooth then thump,over and over and over again. Its a single thump every 4, 5 seconds. Seems during these thumps something is going to give and break.

 

[Frank Acampora]

Re: motor thumps

Noah, if this is happening on the water in gear, it is an indication that it is jumping out of gear. Possible causes are worn drive dogs--which should not be, since you have just rebuilt the lower and should have seen them, or incorrectly adjusted shift linkage. Insufficient travel in to forward will allow the dogs to periodically disengage at speed. The engine will thump and lurch on the transom. Try pushing down hard on the linkage inside the engine cowl while someone else drives. If this lessens or stops the problem, adjust the connecting hex to lengthen the linkage a bit. Do it a little at a time -- if you go too far, the engine will not engage reverse. Equal throw in both directions is best, but if you still have problems, you can bias a bit toward forward since reverse typically gets way less loads on it.

 

[noah4009]

Re: motor thumps

Noah, if this is happening on the water in gear, it is an indication that it is jumping out of gear. Possible causes are worn drive dogs--which should not be, since you have just rebuilt the lower and should have seen them, or incorrectly adjusted shift linkage. Insufficient travel in to forward will allow the dogs to periodically disengage at speed. The engine will thump and lurch on the transom. Try pushing down hard on the linkage inside the engine cowl while someone else drives. If this lessens or stops the problem, adjust the connecting hex to lengthen the linkage a bit. Do it a little at a time -- if you go too far, the engine will not engage reverse. Equal throw in both directions is best, but if you still have problems, you can bias a bit toward forward since reverse typically gets way less loads on it.

Hi
I have the motor in a garbage can filled with water. This is happenning in neutral. When I start the motor in neutral it happens like I said every 4, 5 seconds. Now I do ned to make adjustments cause I had a hard time putting it in reverse, but not hard at all to put in forward. Again in neutral it makes this thump. When I got it in forward it did not make that thump. It was smooth. Frank if you read this read my post on water coming from top spark plug, please.

 

[Matthew A.]

Re: motor thumps

Considering the L.U. was just rebuilt, perhaps the spacer washer that goes between the clutch dog and the forward gear on the prop shaft is not the right thickness. Could also be an incorrectly shimmed drive shaft bearing.