Front main bearing removal

[jamesheath]

I'm setting up for this, now that I've decided the crank has to come out....
I'm going to gently warm the front of the crankcase in a water bath to 60 then push on to 80 deg C if I have to.
I'then supporting the front of the crank, and I'm going to gently drift it out - my question is about which bit I should have the drift on - the notch in the crank allows good access to the inner race, but I can also just see part of the outer race hiding behind the lip of the crankcase - should I be drifting both or just the inner one?
One further thought - it seems to me that I could make a bodged tool that jacks them out against the thread that retains the flywheel on the other end of the crank, rather than doing it against the housing as suggested in Doug Woodrow's excellent book - is there a good reason why it's not done this way?
Thanks

James

[Chris KC]

James, no doubt others know more than I but here's my tuppence:

I wouldn't immerse it in water; A7 crankcases are quite resilient and you can happily play a blow lamp on it around the bearing housing as long as you don't go crazy (massive heat or stay on one spot too long). This will easily bring it up to suitable temperature without negative consequences (such as filling things with water). Heat will certainly help.

Aim your drift at the inner race only. You will need something long and thin, I have managed it with a long wire tent peg before though ideally something slightly stiffer. I guess in an ideal world it would have a 'soft' bearing end - at least try to avoid gouging the casing too badly and don't smack the bearing retaining lip!!

Lots of small taps rather than great big wallops, doing your best to move the drift around the race (I know, there isn't much scope) to avoid canting it sideways. Then it is just perseverance.

Place something soft under the front to catch the front race when it falls out! They are often re-usable but best not dropped on concrete floors from a height.

You may find they are actually not that tight at all, but don't be tempted to put them back in with Loctite. It is mainly the axial clamping force (if anything) that stops them spinning in the housing.

Oh yes, and keep the rear bearing in to hold the shaft straight while you drift, you don't want the crankshaft twisting them into the case.

[John Mason]

When I fitted my new Phoenix crank I removed the old one as per Woodrow but did it with a small butane gas blow lamp moving it around the area until it was warm. Not really that hot. It then came out easily using the brass drift method as outlined in Woodrow. With care it is not as dangerous as Woodrow makes out. When they come out watch out for a possible shim fitted between the two bearings (not always fitted) but was the practice used by some mechanics years ago, I believe it was to put pre load onto the bearings.

John Mason.

[Howard Wright]

Hi All

On my last build I managed to get permission to use the domestic oven.   Lined it with foil and stuck most of the crank in so that the door remain ajar. Although set at 100 degrees having the door open reduced the temperature a bit. I have a length of 8mm stainless rod to use as a drift but after heating it almost fell out.

Good luck

Cheers

Howard

[Steve Jones]

Use an electric fan heater. Set it up to blow into the front of the crankcase from a minimal distance. Leave for 20 to 30 minutes. No flames, nothing to hold, no risk of overheating anything and you'll be amazed not only how hot the crankcase gets but how easily the bearings come out. As said above, don't glue them in when you reassemble.

Steve

[Chris KC]

Sadly Howard we had to buy a new oven just before lockdown and the crankcase is not allowed in there any more!

[Bob Culver]

Hot air guns project a lot of heat. Hopefully the crank will prove uncracked... by looking can deny yourself possibly thousands of miles of use! Dunno your plans but if the engine has been running the fit must be within easy scraping range. Certainly vastly easier with the crank out.

[Jamie]

I did this last week and can echo Steve's comment about a fan heater. I put a 2kw heater on full and left it blowing on the case for about a quarter or an hour or so. It heated the case well enough that I could drift the bearings out with a short length of 1/4" brass rod. The bearings came out fairly easily.

Jamie.

[jamesheath]

Thanks all.
That's now done & was indeed MUCH less painful than Mr Woodrow led us to believe.

In case it helps others, here's what we did.

We used two lengths of 10mm brass rod, along with some wooden blocks to help hold them in place (one with two holes down by the bearing, and one with two notches wedged at the top)
(I have been cautioned that steel would be better - the race is hardened and won't be damaged and with brass you risk contaminating the bearing with flakes of brass, but I ony had the bits of brass)
A lump hammer then spread my gentle taps out to both drifts:
   

We also knocked up a rig to support the crank and let the bearing progress out:
   

We then dropped the crankcase in to a warm water bath (60 deg C) (we didn't have a fan heater to hand - a much better option) - yes we'll get everything warmed & dried after!:
   

We then dropped this on to the rig (thermal image):
   

and tapped away - the inner race moved  nicely down the crank until the crank ran out of travel and impacted the crankcase.
Back in to the HOT water bath (up to 80 deg C), and on coming out of that, the front outer race pretty much fell out, and it was all gentle taps from there.

Probably overly complex, but it felt nice and controlled to me and didn't need any specialist tools (or use of the oven, from which I am banned!)