YAMAHA F25 F30 F40 F50 colour bearings

[almetelo]

Next week must receive parts for the F40 that a buddy brought me from US.

Yesterday had the crankshaft polished e checked/measured at the machine shop.

Chankshaft have some wear and some main bearing marks (the guy at the machine shop said is common these 3 cyl cranks have more wear as motor doesn´t work so balanced as Ex: 4 cyl) but journals are within specifications 42.984 mm - 43.000mm (less one is 42.97*)

The guys at the machine shop are the best around and said thats not a problem.

Crank pins diameter are within spec 32.984mm - 33.000mm

If after plastigauge the bearings aren't within spec I will need a larger diameter bearings. I ordered black "B" main bearings as are the specified for that block/crankcase,

Since yamaha and most if not all outboard manufacturers don´t offer oversized bearings I tried to look for an answer googling for the diference in coulour bearings thickness (which is almost none) but had no luck, than tried to have a look on my data and got the answer on a F45A, F50A, F50B, T50 (U) and F50 (U) 1996 service manual.


This bearings are used on F25, F30, F40, (F45), F50 and maybe others but check yourself.

Have a look:






I hope this can help someone in the future.

Good luck

[boscoe99]

To me, Yamaha is wierd, wierd, wierd when it comes to bearings.

The service manual first shows checking the bearing clearance using plastigage. The manual then details how to select the appropriate bearing. Seems that the bearing would be selected first and then that bearing would be checked to ensure that it is proper. Oh well.

Although not stated as being an "over size" bearing, the three bearing colours represent bearings of different thicknesses; therefore, one of the bearings is thicker than the other two. In your case, the main bearings are blue, black and brown. Black is in the middle which indicates to me that either blue or brown are thicker than black. Let's presume that brown is the thicker bearing.

You say that one of the main journals is slightly below specification. You check the clearance using a black bearing as specified in the service manual. If the clearance is too great the manual would have you reject and replace the crankshaft. However, it might just be the situation that the use of the brown bearing would give you the correct clearance. But Yamaha does not make mention of this at all. Why?????? Who the hell knows?

I won't ever get into the situation where Yamaha species a bearing of one thickness on one side and a bearing of a different thickness on the other side.

[99yam40]

I won't ever get into the situation where Yamaha species a bearing of one thickness on one side and a bearing of a different thickness on the other side.

Do they do that?
I would not think mixing the half's would be a good idea

[almetelo]

Yam, In case of change the bearings from one journal would be the set (2) and not 1 half (IMO)

Yes, Boscoe is strange and on this YAMAHA isn´t a costumer friendly as they seem´s just want to sell parts...

I just found this on 1996 SM (1995 was the 1st year of production of the F50)

I have not all years SM but maybe this data /info was omitted in the following years

[boscoe99]

Yam, In case of change the bearings from one journal would be the set (2) and not 1 half (IMO)Not always. See diagram below.

Yes, Boscoe is strange and on this YAMAHA isn´t a costumer friendly as they seem´s just want to sell parts...

I just found this on 1996 SM (1995 was the 1st year of production of the F50)

I have not all years SM but maybe this data /info was omitted in the following years

Here is the bearing selector chart from an F150 service manual. If the different bearing colours indicate different bearing thicknesses (what else could they be) then this chart shows the use of a bearing of one thickness/colour on one side and the use of a different bearing of a different thickness/colour on the other side.

Strange but true. Does not make sense to me but apparently it works.

[boscoe99]

Do they do that?
I would not think mixing the half's would be a good idea

Yes. See above. I don't make this shit up.

[99yam40]

I guess it is called fine tuning the oil passage/ clearance

[Yamahataos]

A lot of Japanese car manufactures use on there engines different size bearings on diferent locations on there crankshaft and conecting rods I know honda does and Suzuki, usually the darker colors are thicker .

Don

[almetelo]

Hi!

What is the socket for the piston connecting rod screws, 12 point #8 socket, right?

[rodbolt17]

typically its 12pt 8mm or 12pt 5/16ths.

the trick is to not only match the bearing ID to the crank journal but you also have to math the bearing shell OD to the crankcase bore.

can be a pain.
I have only done two little motors and a handful of F250's.

the f250 in triples or twins have an occasional backing down issue where you can force water up the ex and bend a rod.
typically when the operator is backing hard with one (or two) engines and allowing one to remain at idle.

[boscoe99]

Rodbolt, have you ever heard of someone taking a slightly undersized crankshaft (which Yamaha would say should be scrapped) and using any of the available Yamaha bearings to try and get the clearances within specification?

Or, have you ever heard of someone having a machine shop build up a the crank journals and grind them back to within specifications?

On a twenty plus year old motor that is not worth squat I might try something like this before buying a new crankshaft or scrapping the whole motor.

[rodbolt17]

nope, usually here in the salt pond we scrap them.

years back machine shops would weld up and regrind journals.
I actually did it once.
now the labor cost may make it prohibitive.

I also ran a piston knurling machine back when I had blonde hair .

[99yam40]

That would be a good question to the machine shops that work on the cranks.
And if they do what the cost would be

[boscoe99]

I was thinking with the advent of all of the high technology tooling and machinery available to an engine shop that the labor required would have gone way down. In other words, the machinery is now doing most of the work as opposed to a machinist doing it. To a higher degree of accuracy byt the way. Yes, the cost of the machinery is way up but hopefully its cquisition cost would be spread over many a crankshaft.

Price of a Yam F225TXR crankshaft is about $900.00. Here is a shop that offers to regrind a crankshaft for $65.00. Seems abnormally low. Double that to build up the surface before the regrind and it is still less than $150.00.

Cylinder Head Services, Crankshaft And Grinding Services, Cylinder Block Services, Internal Engine Parts, Precision Crankshaft Service, Inc, Jacksonville, FL