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Author Topic: M90 Loose Crank Shaft Bearings ?  (Read 675 times)

70Rcode

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M90 Loose Crank Shaft Bearings ?
« on: February 03, 2020, 11:40:53 am »
Hi all,..Anyone notice the very Loose main crank shaft bearings ??  Compared to usual Quiet running & feels just rite clearance bronze (Oilite) bushings, the crank is really wallowing around & making a roller type noise racket & has got to be dping a number on the crank journals ! ..Just don't feel or sound rite to me..Anyone else notice this on their new M90 ?

rodnoc

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #1 on: February 03, 2020, 04:40:26 pm »
..Anyone notice the very Loose main crank shaft bearings ??

Yes.  It's the norm with the needle bearings.  They do make a bit of noise.

Steamandoil (Tim)

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #2 on: February 03, 2020, 08:19:59 pm »
The crank does make some noise but it doesn't seem to hurt anything. My M90 has a lot of hours on it. I noticed the slop in the mains right away and it has never got any greater. Mine has split brass plain bearings. Take it apart and take a look. My split bushings show a trace of wear- just shiny. Be sure and note the position of the timing gear for the cam. The piston and rod comes out easily on the crank for ring service. If it starts really hammering, most likely ready for a new ring or rings.
If you play with fire, you're gonna get burned.

Nick

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #3 on: February 03, 2020, 08:46:54 pm »
I also noticed the slop out of the box, but I guess that explains the price compared to the alternative.
Nick

rodnoc

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #4 on: February 03, 2020, 11:31:27 pm »
When I get a chunk of free time, I plan to turn some brass bearings for my engine.

For those without a lathe, this vid shows a solid bearing mod.  Can anyone identify what he used? 
https://tinyurl.com/wbovwyb

70Rcode

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #5 on: February 04, 2020, 02:53:31 am »
Hi rodnoc (what a cool handle),..thanks for the very informative video link !  It looks like he's using bronze-aluminum bushing With self lubricating Graphite plug inserts. The gear-train "chatter" noise reduction  is noticeable & usually indicates more than a little bit of gear mesh issues going on. Also, loose fitting,hardened steel needles pounding directly on the crankshaft journals can't be good &
 definitely gonna leave some wear marks that won't "buff out" that a simple, less expensive plain bronze straight bushing (with or without self-lube features) will certainly eliminate. The usual spur gear mount spacing distance tolerance (> 0.001" for class 8 gears) seems needlessly exceeded & would really "bother" most owners of this really Cool almost flawlessly executed (for the most part) rare, affordably priced working masterpiece !!  ...Maybe these production execution issues aren't pricing budget (what's another $25) or accidential design issues but rather an intentional, added value,
 ownership mind stimulating, the gift that keeps on giving electro-mechanical challenges that keeps us busy in the workshop, correcting that "just one little thing" i can fix bonus !!

RedRyder

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #6 on: February 04, 2020, 06:10:27 am »
The old blue engines had a crank shaft diameter of .316" while the new ones using the same needle bearing have a .315" leaving a .001" giving us a bit of slop. Still it doesn't seem to hurt. I have no idea why they began using crank shafts .001 undersize. My old blue M90 has many many hours on it and still has no slop.


The correct solid bearing material if anyone wants to try it is Oilite bronze.

Oilite is a porous bronze or iron alloy impregnated with oil.

70Rcode

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #7 on: February 04, 2020, 10:27:42 am »
Thanks for all the good info guys & a relief i don't have defective bearing issue !  ..Tim, that would be big end con rod split bearing shells ? ..Without any oiling holes or grease
 fittings, consistant assurance of critical bearing lubrication seems "hit or miss", drip it down the mostly hidden bearing sides & hope nothing ever runs dry !! ... Initial running frequent bearing wear teardown checks might be a good idea to verify your particular lubricant type & application method is settled on. ..Yep, Gil..despite the bearing & gear backlash noise, it runs good ! ..Think i'll lower the fuel tank a bit to keep all tank levels running on mixer benturi suction to eliminate any possible full tank gravity flow fuel mixture variation effects. What a cool engine  platform to try out various "improvement" H&M setup ideas  !..Thx again, tom.

catman

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #8 on: February 04, 2020, 06:18:39 pm »
I just got my silver M90 about a week ago, and i also have a bit of slop. It does appear to run fine however. With that said I do plan to replace the bearings as I am unsure of the quality. China has thousands of bearing manufactures, some very, very good and some not so good. I will probably go with Boca ceramic bearings., as they are a known quality.

Of all the roller and needle bearings that I have replaced over the years, I have never seen one that used oil for a lubricant. They have all been packed with grease. I see where many have added oil cups to the mains and as 70Rcode  stated you might or might not get any oil to the needles.  I plan to pack the Bocas with "Superlube" synthectic grease as that has worked well over the years on my trailer wheel bearings. I get thousands, if not tens of thousands of miles on well packed bearings,I would think one could go a long time with these small engines with grease packed mains.

Am I missing something about using oil on the mains?

70Rcode

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #9 on: February 04, 2020, 08:49:33 pm »
Hi catman,...thx for the ceramic bearing & grease lube info..my issue is with the crankshaft radial twisting distance control between the 2 main bearings between the 2 flywheels. It seems to more related to the multi-piece needle bearing cage on-axis twisting movement control which a simple 1 piece bearing or bushing doesnt allow. Any needle roller or Ball bearing type which allows bearing cage pivoting twist movement might not effect any desired improvement. I don't know if a pair of ball bearings will significantly improve that or not but it is almost totally eliminated by a pair of simple, 1 piece bushing or bearing type.

yozhek

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #10 on: February 05, 2020, 05:18:53 pm »
Needle roller bearings always seem to have a lot of clearance, in most of the applications i have seen, so i would consider this normal. The needle rollers provide less friction and require much less lubrication than bush bearings so i guess this is why they are used on these engines.  However metric oilite bushes are available from bearing suppliers that are a direct replacement and do make the engine sound much sweeter.
Kind regards
Ade

70Rcode

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #11 on: February 06, 2020, 10:04:08 pm »
Hi Ade, i've fixed the wobbling loose crank issue using Oilite type porusppl bronze bushing with vertical oil hole feed thru mains cap drip sight tube oilers, ensuring adequate boundary layer lubricant type (i like ptfe additive package) & feed rate control with all wobble eliminated (0.0015" clearance). I also added oil hole lube feed to factory con rod big end  brass bearing shells. All cranks should run so smooth & quiet !! Next,  last lube issue is to add a piston drip oiler hole to cylinder liner. Thanks again for helpful info,. tom.



yozhek

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #12 on: February 07, 2020, 04:07:44 am »
Hi Tom,
That is the exact same thing i did to mine, it does make for a very quiet running engine, if a little messy. 
I'm running mine on regular petrol with a bit of castrol R mixed. Castro R is a bit (ok a lot) overkill but i had a bottle laying around and it does smell nice :-)
Kind regards
Ade

RedRyder

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #13 on: February 07, 2020, 04:31:54 am »
Needle roller bearings always seem to have a lot of clearance, in most of the applications i have seen, so i would consider this normal. The needle rollers provide less friction and require much less lubrication than bush bearings so i guess this is why they are used on these engines.  However metric oilite bushes are available from bearing suppliers that are a direct replacement and do make the engine sound much sweeter.
Kind regards
Ade


Hi Ade, Do you have a name, part number, and supplier name for the correct direct replacement oilite bearings?

yozhek

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Re: M90 Loose Crank Shaft Bearings ?
« Reply #14 on: February 07, 2020, 11:51:26 am »
Hi Gil,

I am in the UK so used UK supplier Simply Bearings   https://simplybearings.co.uk/shop/Bearings-Oil-Filled-Bronze-Bushes-Oil-Filled-Bronze-Plain-Bushes/c3_4511_4770/index.html
I used these AM0812-8 Oil Filled Bronze Plain Bush 8x12x8mm or SKF PSM081208A51 Plain Sintered Bronze Bush Bearing 8x12x8mm for direct replacement or these AI0508-06 Oil Filled Bronze Plain Bush 5/16x1/2x3/8 inch if you want to ream the bush and bearing housing to a really snug fit.
The bearing housings will accept 12x10 but i could only get 12x8 but the needles are about 8mm wide inside the cage so pretty much the same.

Kind regards
Ade