Slight knock where should I start?

[Sheetsfa]

I have a 1974 Chrysler 55hp outboard that has a slight knock in it especially when it decelerates. The guy I had bought it from overheated the motor, I took it home put a new impeller and water pump body in it, ran new gas lines, and fresh gas mix and it started right up. Now the problem I have is a knock in the motor the knock is bad enough that you can feel it if you put your hand on the power head. I have good compression at 120psi cold and I have removed the cylinder head and the pistons and cylinder head look great. I have no problem pulling the rest of the motor apart, but what should I be looking for. Any opinions are greatly appreciated.

 

[tater76]

Re: Slight knock where should I start?

Sorry sheetsfa, I didn't see your reply on the last post till today. I can talk you through the teardown if you are still interested. I still think you are looking at rod caps being loose, but when you say knock what exactly do you mean? My 73 55hp does the typical 2 stroke ring ding ding upon decel when in the barrel. I can see that being confused for knock, could you elaborate a little more?

 

[Sheetsfa]

Re: Slight knock where should I start?

It's ok, yeah I did find on the last start up that it knocks on acceleration and even louder on deceleration, when it knocks on deceleration something must be binding because the complete outboard twists a bit, but it does not twist on acceleration. I have removed the cylinder cover and what I van see the pistons and cylinder walls are in great shape other than som carbon build up on the top of the pistons. I don't know if it's true or not but I read on here that rod bearings wont make a knock bit instead a screeching sound since they are roller bearings. So far the only tear down I have done is removed starter, flywheel, carburetor, and the box that all the wires run to.

 

[Sheetsfa]

Re: Slight knock where should I start?

When it knocks on decal it only does it 2 to 3 knocks, not really a constant knock, but like I said it seems like something in the motor is binding.

 

[tater76]

Re: Slight knock where should I start?

Sheetsfa, My motor does this too. When I decel it will do the typical 2 stroke ding ding, and jerk side to side a little "twisting" the motor then settle into idle. Mine has always done this. You are right about the bearings screeching though. How familiar are you with 2 stroke motors? Every outboard I have ever owned has had this same sound and reaction. However, if you feel that something is definitely wrong internally there is no harm in pulling the case apart to check. I will post some pics of the internals in just a few, give you an idea of what you are looking at.

 

[tater76]

Re: Slight knock where should I start?

Here are some pics of the case split. All the internals are gutted, pay close attention to the damaged areas and the hole in the main block. This is from a thrown rod. I found the cap jammed into a crevice in the case, I had to pry it out with vise grips and a long bar. So... replacing the orange seal and torquing the cap bolts is relativelt cheap and easy compared to a hole in the block.

 

[Sheetsfa]

Re: Slight knock where should I start?

You know I'm not real familiar to 2 strokes. I might be more paranoid than I need to be, I'm just on of those people who want everything to be perfect and I don't want to do anything that is going to cost me more in the long run. It eases me a bit to know that your motor does the same. I think I will go ahead and pull the rest of the motor apart especially since what I can see so far the gaskets look original and in bad shape. Are you able to feel the knocking sound in your motor? Another question is what spark plugs are you using, mine are I think ngk I know they are 18v and don't have an electrode on them.

 

[tater76]

Re: Slight knock where should I start?

I am running ngk's now, can't remember the exact # maybe 68..something. However, I have run L82c champions in it with no issues. You will likely get debate over that. Oh, and running with or without the electrode is also a debated topic, I have tried both on mine and felt no difference. Back to your teardown, if you do in fact want to replace all of the powerhead seals the kit is available here on Iboats. It does not contain the lower crank seal though. I ended up reusing mine because I got ahead of myself wanting to get it out on the water asap. Take LOTS of pictures before and during teardown, this saved me big time. Also, the allen head bolts that hold the case halves together (there are six of them) are different lengths. Use a peice of cardboard to shove them into in the correct pattern, it will make life easier upon install. Get a manual, if you don't have one let me know I can email it to you. Just a thought, if you have it that torn down you might think about new rings and a light hone job? Its not alot more money at that point, and you can borrow the hone from your local auto part place.

 

[Sheetsfa]

Re: Slight knock where should I start?

Yes I will go with new rings, and I will take your advice on the honing. I do have a manual for the motor it's a seloc, what I don't like is that it's meant for so many motors and jumps around alot. I will figure it out though. Thanks for the advice again and I'll keep you informed of the progress.

 

[tater76]

Re: Slight knock where should I start?

Its not a real difficult process, just alot of parts and peices to remember where they go back. The worst part is cleaning the whole dang thing LOL. Oh, very important! when you unscrew the rod cap bolts be careful. There are (I think if I remember right) 16 roller bearings per rod, if you gently pull the cap off they may not fall everywhere. I tilted the motor so I could cup my hand under the cap, then removed it slowly. Main point being don't lose these bearings, remove the cage, bag them together. Rod caps must be put back exactly as they came off, as well as the bolts. your manual will outline this. When you reasemble the rod bearings use heavy grease to hold the bearings in the cage. I used white lithium, but I am sure there are better assembly greases out there but its what I had handy. Then I oiled everything before I put the cases together. I used 10w30 on all of the bearings and moving surfaces, not a ton, but enough to lube it for initial start up. Let me know if you need help

 

[tater76]

Re: Slight knock where should I start?

Just had a thought sheetsfa, you said you felt the "knock" upon acceleration? was it like a hesitation/stutter? that could be other things, ie carb adjustments, timing, etc... However, I think the decel "knock" is normal. Remember, your and my motors are not worth more than $500-$600 in running condition. Don't put any more $ into it than absolutely necessary. I am a glutton for getting these old buggars going again, but we must be reasonable. Start cheap

 

[Sheetsfa]

Re: Slight knock where should I start?

I agree, yes on acceleration the knock is not as loud. I had planned to check the timing. I got a really good deal on this boat, it's a 1964 Glaspar in good shape other than needing a paint, the trailer and motor for $200 the guy was moving and couldn't take it with him. So far between buying the boat and replacing the water pump body and impeller, new gear oil, and safety equipment I only have about $400 in it now. I don't think I will pull the rest of the motor apart but I am glad I pulled the piston cover and exhaust cover because the gaskets are worn especially the head gasket it was actually brittle in places and it probably would have blown out. And after removing the fuel pump cover I found that the fuel pump diaphragm had some tiny holes in it, I'm surprised it was even pumping fuel. From looking at the prices of individual gaskets I might as well buy the complete set now. I will replace these gaskets and the diaphragm and put it back together and check the timing and carb now. If worse comes to worse I'll just have to take it apart again but it only took me about 2 hrs to take disassemble as far as I did and if there is a next time it should be even faster. I'm going to order my parts today so hopefully I'll have them early next week.

 

[Sheetsfa]

Re: Slight knock where should I start?

Hey tater76, well I got my gasket set and head gasket in today. The head gasket is the wrong one, I called Mallory to get the part number from them before ordering from iboats but it is definitely not right. Do you know what the part number is to yours and the manufacturer so hopefully I can track one down? The part number to the one they sent me is 9-63804 and it says it replaces part number 18-3854. Thanks.

 

[carholme]

Re: Slight knock where should I start?

Sheefsta;

Do you have the model number of your engine as the 74 Chrysler 55 head gasket comes up as a p/n F201529-1, which cross refers to a 18-3856. The OEM is still available for about $35.

Do you have a parts listing?

Gerry

 

[tater76]

Re: Slight knock where should I start?

Yes 18-3856 will fit this motor, This is the gasket I used on my 73. It is also the head gasket for 84-(I think to) 87 Force 50hp.

 

[Sheetsfa]

Re: Slight knock where should I start?

Yes the 3856 is the right one it looks like, unfortunately iboats couldn't find me a part number so Mallory told it was the 3854 they were wrong though.

 

[Sheetsfa]

Re: Slight knock where should I start?

Hey tater76, hope your doing ok. I have a question for you, when you have your throttle in the wide open position is your throttle plate at a wide open position?

 

[tater76]

Re: Slight knock where should I start?

I'm great thanks for wondering hows the build coming? When you say throttle plate are you referring to the stator plate under the flywheel that rotates as the throttle is opened or closed? If this is what you are wondering about, then I will just say that I have the timing set at 30 degrees btdc. Let me know

 

[Sheetsfa]

Re: Slight knock where should I start?

No I'm talking about the the butterfly plate inside the carburetor the first on is the choke but it has another inside and if I'm understanding the manual correctly it should be wide open in the horizontal position when the throttle is wide open.

 

[Sheetsfa]

Re: Slight knock where should I start?

Now I must say I dont feel confident on setting the timing correctly, did you have a hard times getting it set correctly I know you have the electronic ignition on yours now but I still have the old magneto type would you suggest I just pay someone to set it correctly?