TRX250R.ORG
Workshop => Engine and Bottom End => Topic started by: bonedoc on June 06, 2024, 10:40:09 AM
-
Okay, have my center cases prepped. Have all the bearings and seals installed and was going to start assembling my center cases. I have a brand new Hot Rods crank but it doesn't fit my crank bearings. I know it is an interference fit. The new crank matches my old crank at 28.03mm in diameter. The crank bearings are SKF 63/28 but the inner diameter of the inner race is approx 24.5mm. Wayyyyyy to small for an interference fit.
Has anyone ever run into this? I have a Crank puller/installer tool but this appears beyond tight. Unfortunately I don't have any of the old bearings still.
-
So alittle searching and it looks like I was given the wrong bearings, whether they were mis marked or what I don't know. Essentially I was given 63/25 bearings. So now to order a new set.
-
Interesting that the bearing ID doesn’t match the bearing number. I wonder what the SKF “explorer” bearing is. I believe the bearing I’ve ordered is 63/28 C3
Joe
-
Sorry to see this happen. Get all set to put it together and now you have to wait. I have been there many times on various projects. I would suggest Koyo bearings
Also, if you are sweating the bearings, I would suggest leaving the seals out until you get the crank installed.
Best regards
-Jason
-
the 2RS on those bearings means 2 rubber seals.....they removed them.....and I bet they are not a C3 clearance fit - Which all crank bearings must be. Like Jason stated.....I'd source out some KOYO 63/28C3 bearings and do it right.
Honda Part# 91008-KAE-000 or 91008-KAE-731 <- these are the 8 ball version (stronger bearing)
:)
-
I purchased non OEM koyo 8 ball crank bearings off ebay when I did my first R bottom end & had an issue with them. After assembling the bottom end twice & having the crank rotate with slight resistance I ended up removing the koyo crank bearings I got off ebay & got the actual Honda OEM koyo 8 ball crank bearings (91008-KAE-731), after the third time assembling the crank rotated easily like it's supposed to.
-
the 2RS on those bearings means 2 rubber seals.....they removed them.....and I bet they are not a C3 clearance fit - Which all crank bearings must be. Like Jason stated.....I'd source out some KOYO 63/28C3 bearings and do it right.
Honda Part# 91008-KAE-000 or 91008-KAE-731 <- these are the 8 ball version (stronger bearing)
:)
All two stroke crankshaft main bearings are not C3 clearance. C3 clearance is the most common bearing used in electric motors but not in two stroke engines. When the engine manufactures have Koyo or any other bearing manufacture make a large production run of bearings, the engine manufacturer that will be using the bearings will usually request the clearance not be printed on the bearing. Some engine manufacturers use different interference fits on the OD and ID of the bearing. The engineers seldom request clearances tighter than C3 but often request clearances looser than C4 or C5.
There are a lot of general specifications for bearings that are intended to be sold over the counter for small projects or to engineers that are building and testing proto types. The markings on these bearings are accurate and are what they are said to be. If there are clearance, finish, and tolerance, markings on the bearings that were installed when the engines were produced, they are usually not accurate. The inner and outer races for all ball bearing of the same OD and ID, are the same. The internal bearing clearance is determined by the size of the balls.
You are probably asking why the markings for clearance on the OEM bearings in a new engine or the bearing sold through the engine manufacturer dealer network, may not be accurate? Bearing manufacturers often produce large runs of C3 bearings since this is the most common clearance, so they mark the outer race of the bearing C3. Then one of the two stroke engine manufacturers calls a bearing manufacturers and needs a rush order of 10,000 bearings that need a C4.5 clearance. The bearing manufacturer tells the engine manufacturer that we have 100,000 inner and outer races already made but they have the C3 label and it will be two months until we can make your bearings without clearance marking. The engine manufacturer does not care what is printed on the bearing as long as it has the balls installed that gives the bearing the C4.5 clearance, like testing has indicated is absolutely necessary. The engine manufacturer through it's dealer network, is supplying the customer with a bearing that has all of the dimensions that was supplied when the engine was new, even though the clearance marked on the OEM bearing was wrong.
If you buy your parts from Honda or any other OEM part, it will have the correct dimensions that engineers found to be optimal through extensive testing. Guys that are attempting to save money by taking their old bearing to a local bearing supplier or ordering bearings online using the numbers that were on their OEM bearing will often experience problems because the new cheaper bearing does not have the correct dimensions for the application.
The moral of the story: Buy OEM parts unless you have the experience and tools to accurately measure and determine what clearance a new OEM Honda bearing had. Most often it was not a standard mass produced C3,C4 or C5 bearing. If the OEM bearing had a C4.5 clearance, it is going to cost you a lot more than having custom bearings made to Honda's specifications than paying retail cost at a Honda dealer.
-
Thanks for the great info Jerry :D I learned something new.....I was always told to use OEM Crank bearings.....and now I know why! ;)
-
So alittle searching and it looks like I was given the wrong bearings, whether they were mis marked or what I don't know. Essentially I was given 63/25 bearings. So now to order a new set.
Who did you order the bearings from BP Racing? I recommend OEM main bearings.
-
One thing that we in the industrial maintenance world have noticed is an infestation of counterfeit bearings. A rep for skf came by my work and told us about it. He even pointed out some of the bearings we had on the shelf in our store room were in fact not really skf bearings. I’m not saying that happened here, just saying that it happens. I typically only order bearings from a reputable supplier and if I am ordering bearings for my 250R they are oem or from the local bearing supplier.
Loren.
-
I ran into the same bearing issues as Loren when I in maintenance. The machines I worked on were in such a extreme environment that even the "correct" bearing didn't last. I was happy that the China $1 bearings were living for at least 3 months. The boss was happy I wasn't paying $20 per bearing anymore with the same lifespan.
For my personal stuff of course I'll pay the price for quality
-
I personally would not buy any bearings other than OEM unless I absolutely had to.