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ET: Engine (Twin) Too much compression ?

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Howard

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VOC Member
#1
Just about to rip my hair out (the short grey one) !!

Twin engine running well, starting well. Adjusted the multiplate clutch and synchronised the carbs. Engine now won't turn over with Grosset starter (no kickstart). It sometimes struggles over a compression, but not fast enough to fire. Battery ok, even tried jump leads - starter cables get hot and they're well oversized, changed the starter motor for a new one.

Any suggestions?

H
 

Bill Thomas

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#2
Use the valve lifter, I know it's not what the Man says, But other people have done it, And it has worked OK. Cheers Bill.
 

peter holmes

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#3
That is a strange one, clearly adjusting the clutch and synching the carbs would not have any bearing, it is early days for me, having only had my Starter fitted by Francois in February this year, as Bill says, the recommendation is not to use the valve lifter, and I don't, and it works just fine, just barely touch the starter button and away she goes, I can only imagine that you might have some sort of seizure somewhere, perhaps in the small chain of gears that transfer motion from the starter motor to the kickstart ratchet via the sprag clutch, if you had a kickstart you could eliminate other engine/transmission faults I guess, it is a difficult one.
 

Howard

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#5
It worked so well for two years, I took the decompressors off 12 months ago. Starter gears is this afternoon's job. I fitted a new selector pawl a couple of hundred miles ago, so this morning I've been through the primary drive to make sure I'd not done something wrong there.
 

BigEd

Super Moderator
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#7
If it worked before you changed things you have to suspect what you have changed.
Carbs should not affect the starters ability to turn the engine over. Have you taken up all the free play in the clutch pushrod so that the clutch is slipping most of the time?
 

Howard

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#8
If it worked before you changed things you have to suspect what you have changed.
Carbs should not affect the starters ability to turn the engine over. Have you taken up all the free play in the clutch pushrod so that the clutch is slipping most of the time?
No. Turns over fine with clutch disengaged and clutch engaged and plugs out.
 

BigEd

Super Moderator
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#11
No. Turns over fine with clutch disengaged and clutch engaged and plugs out.
Do you mean:
  1. With the clutch lever pulled in the starter motor turns over OK as there is no connection to the primary drive?
  2. With the clutch lever out the starter can turn the engine over if the plugs are out, i.e. no compression to work against?
If the clutch is definitely not slipping under load could it be a problem with the sprag clutch under the kick-start cover?
 

Howard

Well Known and Active Forum User
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#12
Try a jumper lead from the battery earth to the motor, sounds like a bad earth to me.
It's not earthed through the body, it's got a 70A earth cable back to the battery, but I like your thinking - I'll start at the earth brush and check everything again.

All the gears and spragg clutch are good. Cleaned regreased and refitted.
 

Howard

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#13
Do you mean:
  1. With the clutch lever pulled in the starter motor turns over OK as there is no connection to the primary drive?
  2. With the clutch lever out the starter can turn the engine over if the plugs are out, i.e. no compression to work against?
If the clutch is definitely not slipping under load could it be a problem with the sprag clutch under the kick-start cover?
1. yes
2. yes - spins everything quickly with no sign of strain until I put either front, rear or both plugs in.
3. no - it turns until the motor stalls and the cables get hot. I've got a car battery to it now with 30A jump leads and they start to smoke when the motor stalls.

I hope I'm soon going to look very silly and find something I've overlooked, because I'm running out of ideas.
 

roy the mechanic

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VOC Member
#14
If the leads are getting hot, it sounds like the starter motor is drawing too much current. Ideally you need to come up with a heavy duty ampmeter to measure the starter "draw". I'm sure Mr Grosset will be able to tell what the draw should be. If I'm on target the motor is finished.
 

Howard

Well Known and Active Forum User
VOC Member
#15
If the leads are getting hot, it sounds like the starter motor is drawing too much current. Ideally you need to come up with a heavy duty ampmeter to measure the starter "draw". I'm sure Mr Grosset will be able to tell what the draw should be. If I'm on target the motor is finished.
Swapped for new motor - same problem.
 

clevtrev

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#18
It's not earthed through the body, it's got a 70A earth cable back to the battery, but I like your thinking - I'll start at the earth brush and check everything again.

All the gears and spragg clutch are good. Cleaned regreased and refitted.
Regreased ? The amount of grease required is merely enough to just SMEAR the faces of the sprag. Any more than that is enough to stop the pivoting of the sprag inserts, that in turn means that the unit will slip , and not drive. Any further problems send the unit to me and I will check out.
 

Comet Rider

Well Known and Active Forum User
VOC Member
#19
Howard,
Although I maybe criticised by Trev, I feel that the gauge of the cables used by F Grosset is to light.
I re-wired a bike for someone a few years back, and went for much better heavier gauge wires and had no further problems

Best of luck
Neil
 
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