Is this Rod Knock on my Yamaha F100?

[Slab]

Sure don't sound right?



Anyone else have an older four stroke yami, does it sound like this?

You may know that I bought this engine locked up, and I took it apart, put new crankshaft bearing in it and put it together. It had all sorts of problems including carburetor issues. But now I have it running on all four cyls, but sounds "not so good".

[gunwhatgun]

I haven't messed with a ton of four stroke outboards. I am still running 2 strokes on everything I have. That being said, something doesn't sound right. How did the pistons and rings look when you had the case split? If you don't split the case to do a bearing on a Yam 4 stroke then please forgive my ignorance, again, never worked on one lol.

[Kevin22]

Why was it locked up? Did you check cyl walls and piston rings? Whats the compression look like? I hear it and it sounds rough. Knowing why it was locked up could narrow it down without having to tear it all apart.

It does sound top endy though

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[Slab]

Well, it's kinda a long story. The previous owner said it was locked up, but when I got it, it was not. Here's some more history from the previous owner. He said the engine was rebuilt by a shop. The head was replaced, the block was replaced, and the oil pump too (I did see paper work). He ran it for 3 months (only on weekends), then it overheated, and locked up. The shop did not stand by their work (and subsequently went out of business), so he sold it to me. Supposably no-one opened it up till I got it.


I opened it up, found a blown head gasket. I also found a ton of junk in the oil pan, and I mean a ton. It was obvious to me that when it was rebuilt they never opened up the midsection to clean out the debris in the oil pan and the oil pickup.


I am a garage mechanic, and although I have done a lot of stuff, I have not dealt with any bottom ends. When I inspected the main bearings it looked like a lot of debris was run through them. The rod bearings looked OK, and the cyl walls looked OK too. Not great, but OK. I ball honed the cyls, replaced the main bearings, polished the crank, and put it all together again. That's it. But once back together it ran like garbage. I found that the carbs were filthy. I cleaned them, replaced a few parts on them, and finally got it to run on all four cyls (I think). I prolly missed some stuff, but this is kinda where we are at right now.

Oh, I have run compression tests and they are OK too. Long story behind that, but they are OK, anywhere from 120 to 150 (I should really redo the tests). I guess just to complete the story on the compression, I eventually found that my compression guage was not screwing in and sealing good, so I thought that was the issue. But I used a press on compression guage and it's fine. The screw in type don't work great on yamaha's, at least not mine. Yamaha has a deep spark plug hole that is like counter sunk. Threads don't go all the way out. Very weird if you ask me.

[Rojo]

Have you connected a Yamaha 4 stroke tach yet? if low or no oil pressure you get it on the tach.

[Kevin22]

Do you have oil pressure gauge you can hook up? Not enough (or any) oil getting to the lifters is a possibility. Valve clearance look okay? I really think it sounds top end.

Maybe some junk made it past the pump and is in the passages still. Id check filter for nuggets now that you ran it again as well

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[DockShootinJack]

Has the wrong sound to be a rod to me. I am like above sounds like something on the cam shaft

[Slab]

I do have good oil pressure. I had a guage on it forever, I removed it right before this video.

And yep, I have checked the filter too. I found maybe one sparkle and that it. I bought a bunch of filters and plan to check it often. lol

I really did not check the lifters, I did not touch the valves other than to make sure they sealed. Yep they held wd40 overnight so I think they are good.

"Yamaha 4 stroke tach" hmm, I'll have to look that one up, dono, is that a simple tachometer?

[Kevin22]

Id check valve clearance especially if the motor ran hot and locked up.. who knows what backed off or warped.

Intake 0.20, exhaust 0.34

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[Slab]

I just did a rod bearing test thing I seen on youtuby, where you try to push on the piston through the sparky hole, when it's "going down" in the cylinder. And I found no play. Hmmm

So maybe some of yous is right, could be top end. I did not do anythin with the the head, but I guess I should somehow check for clearance, Clarence!

And who knows, maybe it's all just fine, and I'm crazy over thinking it. I should just put it on a boat and run it, and then check the oil filter for piston parts, right!