Iflyglow

My Feedback: (79)

I am just finishing my decarboning and bearing replacement on my "High Time" Tower .75, and and am wondering what type of bearing to put in it (shielded or sealed). I have a set of bearing here from RC-Bearing's that I purchased a few years ago, but the front is just a 608-2ZZ (sheilds) and Pauls new bearing set comes with a 608-2SS (sealed). The original bearing had one seal.
After the crock pot and Antifreeze all of the Burndt on Castor Carbon has come off, and it is time to put the baby back together. I measured the crank to crankcase clearance at .0025. The only concern I have is the little groove machined in the cse bore to lube the front bearing. Will it leak air of blow fuel with the sheilded 608, or should I toss it and order a 608-2SS (sealed for it). After the many many gallons of fuel that have been run through it, the engine shows no wear, and looks like new on the inside.

ArcticCatRider

My Feedback: (6)

I would put what was there before. I think the sealed is the way to go.

As far as oil pissing out the front, I've heard conflicting reports. Some have stated that the sealed bearing keeps the front from leaking, while others have said it's the clearance between the crankshaft and the crankcase.

How did you measure the inside diameter of the crankcase? With an inside mic or a snap gauge?

PS: THe rear bearing should be open...and only 1 side of the front bearing should be sealed. If the bearing comes with two seals, get a little scratch awl or a hook and take one out. Then face the seal towards the prop.

w8ye

My Feedback: (16)

Either bearing will work fine.

On the Tower 75, the sealing of the front of the engine is more a function of crankshaft tocrankcase fit than the style of the bearing

Iflyglow

My Feedback: (79)

I used an inside mic. I think the clearance is close enough, but was wondering about the groove machined in it for oiling the bearing causing the problem with a shielded bearing. I don't ever remember a model engine with that oiling groove machined in the Crankcase bore. The rear bearing is of course just an open bearing.
I guess I will have to order a Bearing from Paul, since the local Bearing shop has the 608-2SS in stock, but says that his bearing is not ABEC rated. Paul claims his are ABEC 3.

DarZeelon

David,


Paul McIntosh's advice on the use of a sealed front bearing is as follows:

If a front bearing comes with two contact seals; i.e. 2RS, it is filled with a high-quality grease, which is greatly superior; as far as its lubrication qualities, to any oil-fuel spray that can reach it, from the engine's crankcase.
Furthermore, the seals in that bearing, deprive nothing of lubrication.

So, with both seals in their place, the front bearing will last very long; possibly even outlasting the engine.

A contact sealed front bearing is more RPM limited than an open, or a shielded bearing. But for this bearing size, the contact sealed limit is 20,000 RPM, which is no limit at all.


Just leave both seals in place and install the bearing as received.

Iflyglow

My Feedback: (79)

Dar,
Please read the previous post. THE TOWER .75 SET I PURCHASED A YEAR AGO FROM PAUL DID NOT COME WITH A DOUBLE SEALED BEARING, BUT INSTEAD HAD A DOUBLE SHIELDED BEARING. THE SETS HE SELL NOW COME WITH A DOUBLE SEALED FRONT BEARING. SHOULD I USE THE BEARING SUPPLIED WITH THE SET I PURCHASED ORIGINALLY, OR BUY A NEW SEALED BEARING FOR IT. THE CRANKCASE HAS A SMALL OILING SLOT IN THE CRANKCASE, THAT I AM CONCERNED WOULD CAUSE A LEAK WITH A DOUBLE SHIELDED BEARING ORIGINALY SUPPLIED BY PAUL.

ArcticCatRider

My Feedback: (6)

Motorman I think a lot of motors are like that....I have seen them with both a straight shot like your pic, as well as a curved groove....similar to the rifling on the barrel of a gun.

Iflyglow

My Feedback: (79)

So this feature alone will not make it leak if I go ahead and install the Shielded bearing that Paul supplied me with a a year or so ago. I bought the bearing set by never got around to taking the engine apart to clena the carbon out. It was running awesome, so I did not bother with it.
The stock bearings did not have any rust on them at all, but I decided to swap them out when I cooked the engine in the crock pot. I just don't have a sealed one on hand currently. I did stop by the Bearing shop in town this morning, but his is not ABEC rated that he knows of.

I really like the Crock Pot method for cleaning, since as you can see it removed all of the Carbon from the Piston, and the piston had about 1/32" thick of Hard Carbon on the crown. The Bearings have no rust to speak of, and are very smooth yet, even though the engine has close to 20 gallons through it.

DarZeelon

David,


I understood what you were asking...

I meant that the double contact sealed bearing, is preferable to all other possibilities.
Paul sells it for the [link=http://www.rc-bearings.com/catalog/product_info.php?cPath=30_32&products_id=403]10 cents less than the double shielded ZZ[/link]. So cheaply that you cannot go wrong.

The oiling slot exists in virtually any engine. It will have virtually no effect on the way your engine runs, except lubricating between the crankshaft and the crankcase and making the front rotary valve seal better.


When making sets, Paul first goes the way the OEM did, but after experimenting, he sometimes upgrades his choice... Like for this engine.

Iflyglow

My Feedback: (79)

I installed a 608-2SS bearing from the bearing shop down the street. I pulled one seal off and will run it like the original. I prefer to have engine oil lube it (more lubrication), since I too have seen sealed bearings many times with next to no grease in them. When I purchased the new bearings for my .60NX from Paul, I had to pay an extra $5.00 to get the sealed front bearing since his combo for that engine did not include one either, even though Evolution ships them with a single rubber seal in them. Since the bearings are only a couple cents more, and he claims they are better, then why doesn't he ship them in his bearing sets.

I was just trying to find out if I could run the ones he sold me, or have to order another bearing. I fixed the problem.

blw

My Feedback: (3)

It wasn't clear to me either. I was wondering what came with the engine when NIB.

w8ye

My Feedback: (16)

The engine would not blow any more or less oil if you ran an open bearing up there.

Iflyglow

My Feedback: (79)

To avoid a problem, I just put a single sealed bearing in it, and hope to have the plane back together and flying in the next couple of days. I could have reused the OEM bearings, since they looked and felt like new yet.

w8ye

My Feedback: (16)

I think you will be happy

Iflyglow

My Feedback: (79)

Thanks everybody.

Hobbsy

My Feedback: (102)

David my Fox and MVVS engines do not have front seals in them, in fact the Fox engines have a labyrinth groove cut into the crankshaft that actually screws oil away from the front bearing.

DarZeelon

Quote:

ORIGINAL: MOTORMAN37

...I pulled one seal off and will run it like the original. I prefer to have engine oil lube it (more lubrication)...

David,


By doing that; in contrary to what Paul subscribed, you have in effect 'downgraded' the front bearing's performance and longevity.

Sealed bearings do leak-out some of their grease, but even a small amount of bearing grease will go a long way; and provide much better lubrication for the bearing, than would the rather marginal methanol-oil spray from the engine.


I believe you have erred in unsealing it.

w8ye

My Feedback: (16)

I've never seen any grease in these Chinese bearings. They only have a light oil coating. There's no free oil in them.

DarZeelon

Quote:

ORIGINAL: w8ye

I've never seen any grease in these Chinese bearings. They only have a light oil coating. There's no free oil in them.

Jim,


I believe the lube in these bearings, even if the amount seems small, was found to provide a sufficient lifespan...

I have seen Paul's sealed ceramic bearings ARE grease filled...


I will ask Paul to get into this thread...

Iflyglow

My Feedback: (79)

Dar,
Model engines have been made with open Bearing's for years. I have never ever worn a front Bearing out yet. Maybe if Paul would have sent a 608-2SS included in his bearing kit. I wanted to atleast put a single sealed (inside seal removed) bearing like Tower Hobbies supplies in it (OEM), not like the double shielded that Paul sent Me for the Tower .75 Bearing kit. The original from Tower Hobbies has nearly 20 gallons through it over a span of 7 years. I was tempted to put it back in, since it looked and felt like new yet.

DarZeelon

Quote:

ORIGINAL: MOTORMAN37

The original from Tower Hobbies has nearly 20 gallons through it over a span of 7 years. I was tempted to put it back in, since it looked and felt like new yet.

OK, David.


I wouldn't want to argue with you, for the sake of arguing...

I guess many OS engine owners would envy you, regarding the longevity of the bearings in your engine...[X(]

Bax

My Feedback: (11)

When you see a groove in the crankcase in the upper side of the crankshaft tunnel that goes between the front bearing and the carburetor hole in the case, it's not for getting lubrication to the front bearing, but for pulling oil AWAY from the front bearing. The pumping action of the piston in the lower-end of the crankcase provides sufficient pressure to push unburned fuel through the case to the front bearing. When the crank rotates to where the port in the crank is at the same place as that groove, you have a very low pressure in the case. This will draw excess fuel back into the lower-end. If that groove wasn't there, the engine would spray fuel all over the place through the front bearing. That also happens when the crank-to-case fit becomes worn and the clearance opens up.

[Edit for typos.]

Iflyglow

My Feedback: (79)

And my Liner did not peel either, so I guess they would be really jealous.

Broken Wings

My Feedback: (20)

[sm=thumbup.gif]

Hobbsy

My Feedback: (102)

This is the way does what Bax was saying, the labyrinth groove has a soft substance in it that maybe serves as a sweeper to keep oil from moving forward.