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Putting main bearings in the crankcases

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Putting main bearings in the crankcases
Started at 06:56pm on the 7th October, 2017 by Chris Tindal
Chris Tindal Subject: Putting main bearings in the crankcases
Does anyone have any tips as to easy main bearing insertion into late Redditch bullet cases? I froze the bearings and heated the cases in the oven. In the drive side I dropped in the small outer washer, then the seal, then the large washer, so far so good. The outer ball bearing was then taken out of the freezer and I expected it to drop in with minimal pressure. It was in fact very tight and I had to hammer it home with a drift on the outer race. It was slow going with the bearing sinking in only millimetres with lots of taps. It finally got down to beneath the circling groove but I felt very uneasy and felt like I might crack the housing. I've left the inner roller for now as my circlip pliers aren't big enough for the circlip. Am I not getting the cases hot enough? Should the bearings press in easily? Suggestions welcome...Chris.
Posted: 06:56pm 7th October, 2017
Tim NZ Subject: Putting main bearings in the crankcases
When the cases are at temp, the bearings simple drop into place with minimal effort. Having to hammer them in means you were barely halfway to temp...
Posted: 08:28pm 7th October, 2017
Mark M Subject: Putting main bearings in the crankcases
As Tim says, obviously not nearly hot enough. I cook mine at 250* for half an hour (building up in 50* increments over that time) before attempting this job on a Bullet and I put the cases back in the oven between outer and inner bearing fitting to get back up to temp. A few minutes won't hurt the fitted bearing but will get your clearances back. And also, I keep the new bearings packed in ice while keeping to hand between fittings.

REgards, Mark
Posted: 09:23pm 7th October, 2017
binary Subject: Putting main bearings in the crankcases
Yes you need to heat the cases up more or leave in the oven longer. My bearings just slipped in with out having to put them in the freezer. You must have got the heat ok to have dropped the old bearings out. I have an old electric stove in my shed that I use its oven for this work. My old $20 stove is very handy for doing a lot of different things on and in.
Posted: 09:26pm 7th October, 2017
John M Subject: Putting main bearings in the crankcases
Glad you asked Chris, I'm approaching the re-install of my new main bearings, as soon as they drop through the letter-box. My old bearings were a bit of a pain to remove, I will have to leave the case in the oven longer when I re-fit. As far as the cir-clip is concerned, I found that normal thin nosed pliers worked rather than cir-clip pliers.
Posted: 09:36pm 7th October, 2017
Chris Tindal Subject: Putting main bearings in the crankcases
I'll try the plier tip John. Thanks for all the replies, lesson learnt, more heat!! Will it do any harm to the bearings already in when I heat for a second time?
Posted: 10:39pm 7th October, 2017
Tim NZ Subject: Putting main bearings in the crankcases
IF the bearing metal (raceways) change colour by even the slightest tinge during the heating process you will have well-and-truly, 100% totally and irreversibly, fornicated it :-(
To remove bearings so as to re-seat them, a broad flame blow torch licked slowly and steadily around the bearing seats in the crank case would be MUCH better than placing the cases into a Hot oven.
Saturated temps over 120c and polyamide bearing races start to degrade. Hit the plastic cage with direct flame and you have killed it. Temperatures over 150c and the temper of the steel in the bearings starts to be effected. Cool the case down after seating a bearing to preclude any potential excess heat transfer into the bearing
Smacking bearings in or out cold is a surefire way to dramatically reduce its life expectancy AND fornicate crankcases by smearing alloy and destroying the interference fit :-(
May you be forever haunted by 'Spun Bearings' if you insist on cold fit/remove of bearings!
(Praise be for Loctite bearing fit) ;-)
Posted: 02:54am 8th October, 2017
Bullet Whisperer Subject: Putting main bearings in the crankcases
Hi Chris, Don't cool an alloy casing suddenly after heating it enough for a bearing to drop in or out, unless you want to risk destroying that as well. I use a propane / oxy torch to heat the cases EVENLY and up to a temperature where any old oil in the vicinity of old bearings starts to bubble. Sometimes, the old bearings still need to be driven out, even at this sort of temperature, but the new, cool [room temperature usually works for me] bearings should drop straight in. It helps if you have the open bearing housing facing dead vertical upwards and offer the bearing[s] in dead square to the housing. I drop the drive side ball bearing in, fit the clip and spacer, then heat around the area for the roller bearing outer race again for a minute or two, then drop that in. When removing old bearings, if the outer race of the roller bearing refuses to drop out, running weld around the inside diameter will shrink it and get it moving, the same applies to old valve seats. Regards, Paul.
Posted: 09:05am 8th October, 2017
Chris Tindal Subject: Putting main bearings in the crankcases
Thanks Paul, Tim, I'll try the blow torch instead.
Posted: 10:11am 8th October, 2017
Chris Tindal Subject: Putting main bearings in the crankcases
Well all the bearings are in. Had to heat the cases till oil was bubbling out of orifices and spit sizzled. Next time I think I'll get someone else to do it, this bikes already had a history of ham fisted Neandethal owners :-)
Posted: 07:39pm 8th October, 2017
stinkwheel Subject: Putting main bearings in the crankcases
When I used to be regularly fitting bearings/cranks in the shonky eastern european 2-strokes which were all I could afford to buy, the saying was that you needed the casings "Jesus hot".

How do you know they are "Jesus hot"? Touch them. If you say "Jesus" and suck your fingers, they are ready.

These days I take the whole lot to a man with properly fitting arbours and a hydraulic press.
Posted: 12:35am 9th October, 2017
Revband Subject: Putting main bearings in the crankcases
Heat is the best way to fit bearing into alloy castings, using a press is risky.read Tim's post above it can and does damage the housing.
Posted: 08:09am 9th October, 2017
stinkwheel Subject: Putting main bearings in the crankcases
I wonder how they fit them at the factory?
Posted: 02:21pm 9th October, 2017
Bullet Whisperer Subject: Putting main bearings in the crankcases
With a big hammer?
Posted: 04:21pm 9th October, 2017
gord Subject: Putting main bearings in the crankcases
Hello When removing the timing side main bearing of my Constellation, I used a hot air gun with an assembly of made up pins and a machined support ring with a large screwed rod and nuts to gently pull it out. For reassembly of the new bearing I again used a hot air gun and the bearing in the freezer. The hot air gun can be used to keep the case hot while you work and I had no problem at all. I could send pictures of my home made rig if of interest.3
Posted: 09:52pm 16th October, 2017
scotty Subject: Putting main bearings in the crankcases
Hi i also use a heat gun freeze bearings in freezer for a couple of days , had a rel who does woodturning make up a set of hardwood drifts spigot through bearing and lip to sit on outside rim of bearing lets you get bearing square the a light tap and its in. Have also similar but much longer one made so l can change the large gearbox driveside one without having to remove gearbox case from bike ,just have to support outside of box end with something heavy and solid,works a treat but spigot should only go threequarter way into bearing so as not to hit what you use to support g box end.
Posted: 09:03am 18th October, 2017

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