Oil or Grease--needle roller brg. lube

[Brian Rupnow]

On the fall engine project I am building, I wanted very badly to go to a grease filled needle roller bearing on the big end of the con rod, with no inner race but with a hardened rod journal, and grease seals on the bearing. This would have let me run a dry crankcase. Unfortunately, no one sells 3/8" needle roller bearings with seals now. This means I will probably have to run some lubrication in the crankcase. I'm rather torn about what exactly to do now. The engine will be a slow revving display engine, not run frequently and not run under load. It was designed primarily to see if I could design and build a side valve (flathead) engine from barstock with no castings. My gut instinct is to give the needle bearing a good coat of grease and run it that way. Of course the problem is that with a sealed crankcase there is no way to check and see IF the bearing required more grease at some point in the future. The other option is to put a filler tube on the crankcase and run a very small amount of lube in it for the big end bearing. The small end bearing is also a needle roller bearing, but it is pre greased and does have seals, so I'm not worried about it (It doesn't ever make a full revolution anyways, just rocks back and forth). The wrist pin is hardened. I run a small percentage of oil in my fuel to keep the Viton o-ring on the piston lubricated, so the only real issue is lubricating the big end bearing. I am thinking of running a small amount of really "clingy" oil in the crankcase, something like chainsaw chain oil. Again though, since the crankcase is essentially closed, and I will be running only a small amount of oil in it, it becomes very difficult to monitor the oil level. I am open for suggestions that do not include remaking any parts.---Brian

 

[Scott_M]

Hi Brian

If you are talking about these ( see pic below ) I would recommend grease. I have used a lot of these types of bearings in many different applications. Although They have all spun concentrically, never wacking around like the big end on a con rod. Centrifugal force will keep the lube in the bearing cup . The bigger problem is when it is sitting. Oil would run to the bottom and overfill the cup and run out. Grease will stay put.

Scott

 

[Cogsy]

Brian - I don't recall if your bearing fills the entire big end of the rod. If it does I can't help (unless you're open to buying a thinner bearing). If there is room each side of the bearing, you may be able to buy a 'G' seal for your size. G seals are very thin seals with very narrow cross sections and are specifically made to seal needle roller bearings, so there should be one the right size for your application. You could fit one each end and have no concern about your grease escaping.

 

[Hopper]

I have an old Harley that uses an unsealed needle roller bearing of about 3/8" diameter on the commutator end of the generator armature shaft. You just put a small dab of grease on the bearing on assembly and it seems to last forever. Mine has been running since 1977 with the grease being changed just once in all that time, at about 50,000 miles.

So I would say give grease a try. Even though it is a big end bearing, flathead power, compression and revs are all low enough to not need oil for "cooling" effect and lube.

 

[lohring]

This is a little off topic, but grease lubrication works very well under a more demanding application than you are talking about. We were developing a 36 cc engine to set model boat speed records. We found that the crankshaft, supported by two ball bearings was flexing enough to cause flywheel strikes on the magneto. We added another ball bearing on the output end of the crankshaft. We also replaced the magneto with a lighter electronic ignition. This bearing, unlike some other parts of the engine, had no problems during tests to 25,000 rpm and almost 12 hp.

Lohring Miller

 

[gmac]

Brian;
I think this is what Cogsy is talking about;

http://www.schaeffler.com/remotemed...schaeffler_2/tpi/downloads_8/tpi128_de_en.pdf

Page 147 here;

http://www.nskamericas.com/cps/rde/xbcr/na_fr/Needle_Roller_Bearings.pdf


Think I'm going to give them a try, thanks Cogsy!

Cheers Garry

 

[Brian Rupnow]

Something is wrong with the notification of new posts in threads which I have started or posted in---I don't get them for this site anymore. I have no room to add seals. I am going to grease the bearing with some molycote grease and also add a bit of chainsaw chain oil to the crankcase before I seal it up. Cogsy and Gmac--That is quite remarkable--I never knew that one could buy seals as a separate item for needle roller bearings.

 

[OrangeAlpine]

Brian, no expert, but it seems to me if you add oil to the crankcase, might as well forget greasing the bearing. The oil will thin the grease, which will then run out with the oil and you are dependant upon a continuous supply of oil for the bearing.

I think you would be better of with a seal less bearing as the cupped ends will contain the grease. Ford uses unsealed needle pilot bearings on the input shaft of transmissions and they last forever.

Bill

 

[Rustkolector]

Brian,
An engine builder friend of mine has built a couple multi-cylinder 4 stroke engines using only dry sumps and a 60:1 mix of camp fuel and Marvel Mystery oil. His engines have great compression yet blow by enough of the unburnt MMO to keep the entire lower end lubricated. He uses bronze bushings for the main bearings, 7075 or 2024 aluminum for the large rod ends, and bronze for the rod small ends. His engines have many many hours on them with no bearing issues, and his engines are usually quite wet with oil when he inspects the bottom ends. If this isn't enough lube to set your mind at ease, you could also provide and access port in the crankcase to put a good shot of aerosol lube oil into the crankcase when first starting. Slow speed engines actually need surprisingly very little lube oil if they are not working.

Jeff