ET: Engine (Twin) main bearings

[Cyborg]

No Loctite on the mains for my Comet. Near as I could figure, the cases I used still had the original bearing races and just the factory stake marks. The races were a bit of a pain to remove even with the appropriate oven time. The cases were in remarkable condition.

 

[greg brillus]

The factory stake marks were only there to stop the races falling out when the case was flipped over to install the spindles and so on, not to add any extra holding force to retain the bearings. If you have any races that are loose or not enough interference to hold the bearing, you should sleeve the housing, I prefer to do it in steel although others do it in alloy or bronze. It is less effort than you think to do it, and the results tend to work out well. Recently on one engine the customer insisted on plating the bearing oversize and ground to the correct fit. This actually worked extremely well and they ground the OD to the figures I quoted them exactly. Upon heating the case to 180 degrees Celsius the bearing dropped in nicely, as did the other new bearings.The only down side was the plating company seem to have lost the inner race of the new bearing.................Which means I now have to sacrifice another new bearing. The factory specify 200 Degrees Celsius to heat the cases, but this is too hot and is close to annealing the alloy. The problem with installing an oversize bearing or loctiting a bearing in is that generally the bearing pocket is no longer truly round. Years ago to sleeve a bearing housing would be very difficult, but with a CNC mill it is not a problem at all, and not that expensive............To give some perspective.........To plate and grind the new bearing oversize is about $150 AUD whereas to bore the one bearing housing and sleeve back to standard is about $300 AUD. The case that we plated the bearing oversize was a new crankcase, not an original flogged out one, so the hole was round to start with. I don't tend to muck around with loose bearing housings anymore, I just get them machined and sleeved..........A crankcase re-sleeve to do both sides is about $600 AUD for the whole job.

 

[erik]

if a bearing is only hold by locktite in the housing then there is no Tension on the outer ring and the Play in the bearing is bigger,isn`t it? so my crankcases will be machined cnc and what Vic did is very nice. Erik

 

[Black Flash]

Hello Vic,
I am with you regarding your arrangements. As I spent a few years in the bearing industry my first choice would not be a glass reinforced 66 cage.
In a precious bike - which the Vincent certainly is-my option will be a skf bearing with a solid, non riveted brass cage. This type of cage was called ML and probably still is. By the time I left the industry, skf was the only manufacturer to make this kind of cage. These bearings also have logarithmic rollers, which are known to the English speaking friends as Superblend bearings.
Don't get me wrong I won't say the 66 type cage will break, it's more a belt and braces decision which gives me peace of mind.
Bernd

 

[greg brillus]

Just as a point of interest, I have seen a set of chopped cases used in a Norvin race bike years ago, where the complete outer section of the remains of the primary drive housing had been completely removed, the main bearings had been staked with threaded screws or similar to the pictures of Roberts engine above and done 180 degrees apart .............The drive side case had completely split across the main bearing housing straight through where those screws had been and right out to the front of the case. Of course the main weakness was the total removal of the Primary housing thus removing a large strength area of the case. It is very sad to see any engine do this let alone a Vincent engine ........ It is not something you forget............ .

 

[Cyborg]

if a bearing is only hold by locktite in the housing then there is no Tension on the outer ring and the Play in the bearing is bigger,isn`t it? so my crankcases will be machined cnc and what Vic did is very nice. Erik

In that case you wouldn't use a C3 bearing.... which probably shouldn't be used sometimes anyway...... as he lights the blue touch paper and heads for the hills.

 

[Vincent Brake]

well,
my experience only, but ran about with it for 55K km with one bike, with a check at 25K.

Locktite cures very quick under heat, causing a "firm" (well how firm is that) thick film and thus a higher interf. fit, to what sise? and never thrust over full surface...
I always machine up new outer rings, suit to a skimmed set of engine halves ( yes line bore-ing, very boring yes). and a bit wider at the oilpump as well.
no outer radiusses, so about 20% more thrust surface.
Oversise 0.05-6 mm, make the inner dia. about 0,01 0,015mm bigger as over the rollers.
its to small to fit the race in, so hone the 0,01 out with 7-14mu diamond paste and a brass mandrell.
When in situ one gets a zero tollerance (phrase used in other discussions as well). so dont rush off cold.

and yes i agree 3 countersunk M4 screws do weaken the lot, but than again a loose ring tooooooo...

btw crank must be best within 0,01-0,015 measured over the bearing positions,
This is not to be meaured between centers on a lathe....

cheers

Vinnie

PS und wahl mal gut aus al diesen empfehlungen Erik, dan bleibt m Fahren und fahren

 

[oexing]

Bernd, the question about brass cage or modern plastic is a thing of religion: I did not have particularly positive experiences with these once very expensive and old time brass cages, not worth the money. Brass is veeery heavy , worse than steel and I will never again install these rattly heavy cages in an engine. PA 66 GF have a max 120 degrees C permanent so in a classic all roller bearing type engine you will hardly ever see more than 100 degrees , no reason for expecting trouble with them.
Basically I´d go for restoring the correct shrink fit in the engine case and my way would be to downsize the o.d. in the case for the metric type with 62mm so you don´t weaken the case by taking out another millimeter or rather two for a substantial bush. As expected there were reports of cracked cases by drilling screw holes or some such. Only extra job towards metric is to fabricate a sleeve on the mainbearing shaft for 30mm from standard 25.4 .
But in Erik´s case a temporary solution is wanted, possibly by Loctiting loose outer races. A very safe way I came up is to heat case with outer race dropped in up to 120 - 130 degrees, check clearance with fine feeler gauge blades at this temperature , cut 2mm strips from blades for even gap around the race to keep it concentric with four strips of feeler blades - that you can pull out after the Loctite has settled a bit. A very low strength/viscosity type like 221 will fill the gaps around the race in the hot case instantly and at normal engine operating temps at , my guess, 80 to 100 degrees the races will still be gripped with correct shrink fit. In classic times bearing shrink fits were calculated for dropping out at about 120 degrees, 200 degrees seem to me way over top. This kind of heat is required for inserting valve seat rings or valve guides only into alu heads.
Never cared about C 3 or any other classification. In motorbike application you are lucky to operate an engine with good shrink fits after decades and even then that shrink will be next to zero when hot , so why provide extra play in the bearingm for what reason ? Whenever a crank is out of true a C 3 will not help much.

Vic
brass cage bearings :
Roller bearings