Noise in lower unit

[Cuz]

Has anyone ever encountered this problem? I recently purchased a remanufactured lower unit for my '91 Yamaha 150 TXRP engine. It has a clatter, something like a knocking noise at low RPM that goes away around 900 RPM. There is no vibration or noise at high speed and otherwise seems to run fine. I drained and checked the oil and other than normal break in type minute particles of metal and dirty, there is no evidence of damage or water. I'm almost certain it's related to backlash, but seems to be about the normal amount. I was going to return the unit to the vendor, but am fairly confident this well be a waste of time as they will tell me nothing is wrong with the unit, and probably can't duplicate if it's not on the boat running in water. A reputable mechanic told me he knows exactly what the problem is. Said it needs a shim/collar or something under the H2O pump housing, but I can't find this on the parts view and don't remember ever seeing anything like this on my other motor or when replacing water pumps. Any ideas or helpful advice greatly appreciated. Oh, it only make noise when in gear, F or R.

[Cuz]

Here's an update and twist on this problem I've been trying to diagnose. Looking through the parts breakdown on boats.net it appears that the lower unit for a '91 Yamaha 150 TXRP will fit many models from '84 up, but here's the kicker and the rebuilders don't tell you. Beginning in '92 they take a different H2O pump hsg., insert (cup) and some other parts that are not applicable to '91 and earlier models. So, if the rebuilder hooks you up with a unit from a later model engine and doesn't supply the water pump and accessories and you go back with the same stuff used in the original motor you will not have these parts. Unit will run and pump water, but may cause this knocking noise. At least this is my theory. I'll test it this week when I can get parts.

[Ken]

Cuz,
Your motor is one of those twin counter rotating prop models, right ?
Your problem sounds unique - let us know what you find out [img]smile.gif[/img] ,
Ken K

[Cuz]

Ken,

This is my standard rotating unit and I suspect if something weird can happen, it's gonna happen to me. I figure you either gotta be pretty mechanically inclined or rich to own a boat and I ain't rich. I'll keep you and the rest posted with progress. Hopefully, I'll cure my problem and help someone else.

Doug

[jb123]

just the way the gears mesh in lower units will cause the grinding if you engage slowly. i always hit them swiftly..do yearly fluid changes and replace upper driveshaft seals as general maint is about all you can do.

[slim]

it sounds like you need the stainless cup,plastic bushing and three washers under the water pump housing. did you have a stainless prop before? switching to a stainless prop, you will notice a knocking sound coming from the lower unit caused by the heavier weight of the prop verses the alum. prop. try this

[Cuz]

Slim,

Going to try the stainless cup, washers and bushings as soon as I get my hands on them. Seems that's the direction I keep getting. Yes, I still have the same stainless prop as before, I am hoping that the change from '91 to '92 and later when these parts were included will cure the problem. Thanks, I'll post the results once I have a chance to make the repair and put 'er back in the water.

[Cuz]

Put the lower unit back together and ran the boat this weekend. No more knocking noise! Turns out that the washers, wave washer, split collar and stainless collar eliminate the excessive end play in the input shaft. Yamaha apparently changed something from '91 - '92 and later model lower units which requires the later model lower units to take these parts. So if anyone runs into a similar problem or replaces a lower unit from a '91 or earlier model 150/175/200 with a new or reman lower unit, be sure to check this. You'll also have to replace the water pump housing and the stainless cup that goes in the housing to accommodate the additional parts. Too bad the remanufacturer didn't disclose this information. Would have saved me a lot of aggravation; but hey, at least Yamaha still makes parts for 15 year old motors!
Doug

[Ken]

Doug,
Thanks for the feedback [img]smile.gif[/img] .
Are you saying there was excessive end play on the drive shaft without the extra parts for the water pump?
Ken K

[Cuz]

Hey Ken,
You've been quite helpful in the past and I hope I can share some useful info. here. The excessive end play is on the input shaft (long shaft that mates to bottom of crankshaft) and you actually have to "lift" it up while simultaneously driving the water pump impeller down to remove all the end play then install all these "extra" pieces. I don't know what Yamaha did or changed from '91 to '92, but there is a definite difference. If you get a chance, take a look at the parts break down at boats.net. My original model is a 150 TXRP, all the subsequent models, TXRQ, TXRR, TXRS, etc. take the washers, waver washer, split collar, stainless collar and a different impeller housing and water pump. housing. Without these the unit will run fine and pump water, and only make noise at low RPM...but drive you crazy! Sorry to be so long winded, just hope to keep anyone else from going through it.

cuz

[Ken]

Doug,
Thanks again - very useful info [img]smile.gif[/img] .
Ken K

[slim]

the earlier models have a spring setup inside the lower unit under the upper drive shaft bearing housing and didnt need the washers and cup and bushing.

[Cuz]

Wonder why they changed a good design and went with this set up? Seems like they should have left a good thing alone.