Author Topic: B40 tight engine  (Read 1634 times)

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chaz

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B40 tight engine
« on: 04 September, 2021, 19:38:31 »
before I risk a tear down, my rebuilt B40 engine is tight to turn over,  got the back wheel in today with chain and even with plug out in top gear, its still hard to turn over with the wheel and cant use the kick start by hand.
the clutch was fitted and it was the same to turn over, its a complete rebuild/

crank and bigend assembly new and was ok, Im thinking it may be valves need adjusting.? but I only manage to do bits and pieces to the rebuild between other work.

DAVE BRADY

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Re: B40 tight engine
« Reply #1 on: 04 September, 2021, 19:53:48 »
Hi Chaz,

Was it tight before you fitted the head?

Dave.

chaz

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Re: B40 tight engine
« Reply #2 on: 04 September, 2021, 21:37:27 »
Dave, to be honest, I cant remember.
the motor was rebuilt by me last year, then it got fitted into the frame and youngest son had it all back to rebuild. Its been at his until he gave up on it after doing some wiring, he has been on shift 4 on 4 off, with two young kids and I work nights as well as working on my days off at the unit rebuilding and servicing bikes, I would have thought it was ok but cant  remember.
will have a look at valves tomorrow asinlet cant remove cover as carb is in the way so have to make angle flange up which will cure the alignment to the air box mismatch..

AdrianS

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Re: B40 tight engine
« Reply #3 on: 05 September, 2021, 08:07:47 »
Can’t see how the valves would make the engine tight.
Did you turn the engine after the crank was fitted in the crankcase to make sure it wasn’t tight in the cases? Did you turn the engine over after the barrel was fitted to make sure it moves ok?
Unfortunately you may have to start stripping the engine and removing components and hope it is not the crank binding in the cases.
Just out of interest, you say it is hard to turn with the back wheel. Was the bike in first gear when there will be a lot more resistance?

Pete A10

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Re: B40 tight engine
« Reply #4 on: 05 September, 2021, 09:53:35 »
If the engine has been rebuilt was it totally dry? Did you use STP or similar on all the key bearings during the rebuild. May need to inject some oil into various accessible places to make sure things a aren’t binding a bit

chaz

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Re: B40 tight engine
« Reply #5 on: 05 September, 2021, 14:09:09 »
re checked the valves today, inlet was playing up, a look through the inspection showed up the inlet rocker had jumped out of the push rod. loosened the cover and reset valve clearances, now turns easier in top gear and  kick start is better. just have to wait until next weekend to see if I can get it to fire.

JOHN KAY

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Re: B40 tight engine
« Reply #6 on: 14 September, 2021, 23:47:23 »
   

  HI THERE I HAD THE SAME PROBLEM TIGHT ENGINE , TURNED OUT TO BE TOO MANY THRUST WASHERS ON LAYSHAFT WITH NO FREE PLAY FOUND BY SLACKENING OFF TIMING COVER SLIGHTLY THEN ENGINE TURNED OVER OK  SO EASY FIX REGARDS JOHNBOY .

chaz

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Re: B40 tight engine
« Reply #7 on: 16 September, 2021, 12:31:29 »
slackened the primary chain off today, seems a bit better. I suppose being a 350without decompressor, its going to be tight any way.
now to sort the dripping  primary, the joint compound one side/ grease the other didnt work. so its back to compound//compound again like I always have in the past!!

chaz

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Re: B40 tight engine
« Reply #8 on: 13 November, 2021, 16:55:10 »
Ok, back ressurecting this problem again, I dont get to play with it as often as I would like.
Ive pulled the primary off today sprocket and clutch. the crank is still turning on the tight side, so specialists, would it be the oil pump or washers, Im pretty sure that I didnt put any thrust washers back on the rebuild.
I suppose the only way to check is pull the timing side back off.

JulianS

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Re: B40 tight engine
« Reply #9 on: 13 November, 2021, 17:44:46 »
Maybe the crank mainshafts are misaligned?

chaz

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Re: B40 tight engine
« Reply #10 on: 13 November, 2021, 17:59:27 »
The bushing was machined by the same person that has done all my rebuilds, Brit, Jap, Italian etc Ive used for the past 40 years, and currently doing my A50 work. Although we all get off days.
One thing I am considering, would it be the possibility that the engine is  a tight fit in the frame? Ive mentioned before that there are no spacers on the bottom engine mount bolt? also I did have to ream out the frame/ cases to get the front mount bolt in. might take that bck out as its a new item.

chaz

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Re: B40 tight engine
« Reply #11 on: 14 November, 2021, 14:00:40 »
removedthe front mount bolt today, and loosened the bottom mount bolt, engine now turns over easier, not too easy but easier and on the kickstart on the ramp so by hand.
2 pictures, one the front mount and 2 the bottom mount , only has a washer each side not half inch spacers as suggested.

Ive now turned front stud down to see if it will clear easier
« Last Edit: 14 November, 2021, 14:02:15 by chaz »

AdrianS

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Re: B40 tight engine
« Reply #12 on: 14 November, 2021, 14:27:19 »
cant see how loosening the mounting bolts should make any difference unless the crankcase is distorted by tightening them.
I do feel though that the problem is within the engine - either crankshaft misaligned as Julian said or what I feel is more likely the shimming of the crankshaft is not right.
Bite the bullet, get the engine out and strip it down. Take off what you can in the frame to make it a bit lighter if you cant manage lifting it complete ( weighs about 35 kilos).

Pete A10

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Re: B40 tight engine
« Reply #13 on: 14 November, 2021, 17:22:17 »
When I did my B40 I had a local engineering guy rebuild the bottom end. On his first attempt it was very tight and would hardly turn. Stripping it and checking he found that they had not pressed up the crankshaft sufficiently. Gave it a further squeeze and it rotated freely. It does mean an engine strip though. Same effect as having it shimmed wrong.

Colin SS90

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Re: B40 tight engine
« Reply #14 on: 16 November, 2021, 20:20:34 »
Are the crankcase nuts and bolts torqued up correctly? If they are not it could be the frame bolts are further compressing the crankcase halves and causing the crank to bind between the bearings.
1964 SS90