I am about to replace the main bearing bushes on my 102 plus as they are excessively worn and am wondering if anyone has any useful tips for doing this.I intend to heat the crankcase halves and cool the bushes in the freezer,then press them in using a vice.
As the new bearings are of the later type can the engine then be safely run on 25:1 mix?
102 main bearing replacement
Moderators: John@sos, RickUK, charlesp, Charles uk
I've not done it with a Seagull but when I did it with a car gear box bearings there was no need to press them in they were just a rattling fit once the casing had been heated in near boiling water. I do not even remember cooling the bearings.I intend to heat the crankcase halves and cool the bushes in the freezer,then press them in using a vice.
If you do press them in press against a block of wood or something that supports the crankcase halves close to the bearings.
Hmmm.
The bearings should be a push fit; tight but not impossible.
Bearings for a Seagull really need to be reamed to ensure everything's OK. Reaming should be carried out - obviously with the right reamer (!) - with the crankcase assembled and aligned correctly.
There aren't many people with the right tool and the right experience - may I suggest you ask John about this?
Good luck, in any event.
The bearings should be a push fit; tight but not impossible.
Bearings for a Seagull really need to be reamed to ensure everything's OK. Reaming should be carried out - obviously with the right reamer (!) - with the crankcase assembled and aligned correctly.
There aren't many people with the right tool and the right experience - may I suggest you ask John about this?
Good luck, in any event.
-
Charles UK
Stephen there should be 1.5 thousands of an inch oil clearance on new main bearings, to ease manufacturing costs, Seagull had the crankshafts ground 0.0015"small on the mains so they could use a 5/8" super long line reamer on the bearings.
British Seagull did used to carry both the reamed & the unreamed mains for the Century, but I've never seen any for the earlier 102 crankcases.
If you let us know your engine number I will try to remember what your mains look like.
Your bearings will push out a quite low pressure Iv'e done them with the tail stock on a lathe & with a small fly press.
When I pressed them back I made up a mandril with a 5/8" center out of some 1" bar to prevent distortion & held them in with green loctite, I still got some distortion causing it to be quite tight where I had to drill the oil holes, this was on a wartime short water jacket 102, Rather than drive 2 hours to John's to use his longline Seagull reamer I set the crankcase up on a vertical mill & very carefully reamed them parralel.
Your looking at a heap of work to do this, first you will have to find some new reamed Century mains, then modify them to the 102 style, then go through the above steps.
If you pay somebody else to do this the cost will far exceed the finished value, do you really need to do this?
During the war the 102+ was run at 6:1, one & a half pints of oil to a gallon of petrol, perhaps there was method behind their madness.
Though I'm sure a smoke screen is a good thing when people are shooting at you!
British Seagull did used to carry both the reamed & the unreamed mains for the Century, but I've never seen any for the earlier 102 crankcases.
If you let us know your engine number I will try to remember what your mains look like.
Your bearings will push out a quite low pressure Iv'e done them with the tail stock on a lathe & with a small fly press.
When I pressed them back I made up a mandril with a 5/8" center out of some 1" bar to prevent distortion & held them in with green loctite, I still got some distortion causing it to be quite tight where I had to drill the oil holes, this was on a wartime short water jacket 102, Rather than drive 2 hours to John's to use his longline Seagull reamer I set the crankcase up on a vertical mill & very carefully reamed them parralel.
Your looking at a heap of work to do this, first you will have to find some new reamed Century mains, then modify them to the 102 style, then go through the above steps.
If you pay somebody else to do this the cost will far exceed the finished value, do you really need to do this?
During the war the 102+ was run at 6:1, one & a half pints of oil to a gallon of petrol, perhaps there was method behind their madness.
Though I'm sure a smoke screen is a good thing when people are shooting at you!
Thanks everyone for your replies.The existing bearings are very worn,there is a nasty clunk when the flywheel is rocked from side to side,I estimate there is about 15-20 thou of side play which far exceeds the recommended tolerance of 5 thou in the service sheets.Amazingly the engine runs even so but this excessive play must surely have an effect on the points gap.
After what Charlesuk has said I’m a little confused about the correct bearings.The parts lists for the Forty,Century and 102 all list the bearings with same part numbers of 1282 upper and 1284 lower,the service sheets imply that the latest modified bearings that I have can be fitted to all models.
The differences seem to be that the lower bearing has an angled cutout which extends under the oil hole in the crankcase (therefore no hole drilling required) and the upper has a similar cutout and the bush is slightly longer which would give more support to the flywheel end of the crankshaft.Presumably these modified bushes enable more oil to get to the bearings,hence my query about running on 25:1 mix.
I do have a suitable 5/8â€
After what Charlesuk has said I’m a little confused about the correct bearings.The parts lists for the Forty,Century and 102 all list the bearings with same part numbers of 1282 upper and 1284 lower,the service sheets imply that the latest modified bearings that I have can be fitted to all models.
The differences seem to be that the lower bearing has an angled cutout which extends under the oil hole in the crankcase (therefore no hole drilling required) and the upper has a similar cutout and the bush is slightly longer which would give more support to the flywheel end of the crankshaft.Presumably these modified bushes enable more oil to get to the bearings,hence my query about running on 25:1 mix.
I do have a suitable 5/8â€