The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: chaz on 13.02. 2013 21:35
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started the old girl up ready for the MOT now its near after having it 5 years... was running ok before christmas now it seems to have blown the head gasket, runs but pops and bangs a lot and weeps on left side. been told its got flat top pistons. as Ive not been inside the motor since Ive had it any hints and what about the flat tops good, bad ??
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HI Chaz,
I dont believe gaskets fail while sitting in the shed??????
Firstly, check compression on both cylinders
Then sparks, try new plugs??
If the fuel has been sitting for a while drain it off and refill with fresh stuff, it doesnt take long to go off *sad2*
You can also check the head nuts for tightness, its common enough to have a weep from the pushrod tunnel area
Wheres it weeping from??
Flat top pistons are fine for everyday riding
HTH
John
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Hi John, congrats on your 1000th post *eek*
modern fuel is poor, Ive just picked up a 750 guzzi not been on the road for 5 years yet with new battery and a few mins of cranking it started. the A10 has been run but for some reason seems to be dribbling out of the head joint, even seems to be a small bubble around one of the headbolts not weeping but air bubbles. bolts seem tight , just wondered if its unburnt fuel pressurised as tried kicking it over with a flat battery?
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Hi Chaz,
Does your A10 run on mag or some other type ignition? electronic or distributor??
A mag doesnt need a battery???
I dont like the bubbles coming up the boltholes *eek*
quite often the bolts are reluctant to thread any farther into the cylinder due to rust/crap in the threads
something to watch out for when you replace the gasket
Hi John, congrats on your 1000th post eek
Jeez that makes me feel really old *ex* *ex*
Cheers
John
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I must be ancient *conf*.
I've seen bubbles coming from bolts that have had too much oil on them when tightened. When hot the air gap at the bottom of the bolt expands and bubbles the oil out. Flat tops shouldn't blow head gaskets. Check all that OLD John has mentioned.
Cheers
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Hi Musky,
They say that "A man is as old as the woman he is feeling" ;) ;)
John
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Bugga, she's 3 more than me. *spider*
Cheers
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Congrats John on you becoming a Kilomaileter, does your age theory mean I'm best not to take on a job as a toyboy (might have just missed qualifying age by a decade or two mind). edit - like Musky *smiley4*
Now young Chaz flat head pistons are just fine, early bikes had dished ones (6.5 to 1 IIRC).
Compression test as John suggests would be good
would try to find out precisely where the oil is coming from, could be it's leaking oil into the a cylinder and fouling a plug, would examine both.
Yes now flat battery - not a problem if it is magneto for sparks if it's electronic then the test is easy just charge up the battery to full and then try it, most electronic systems seem to default to full advance when the battery gets low, so even if it fired up it would run wrong at low speed until the charging system got the battery up to at least 11 volts
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Jeez that makes me feel really old
Should instead make you feel really helpful and valuable ! Congrats with the 1000 mark.
chaz, some things to look at, cylinder\head surfaces perfectly flat ? Torque wrench for the bolts (and re-tightened after a while) ? Tightening sequence > http://www.a7a10.net/BSA/techpics/sequence.jpg ?
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How did it go ?
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just see a small mark where its been blowing , putting it all back and now one of the rocker bolts has a stripped thread!! got 4 new coming from Drags today.
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I have a similar question.
I paid some serious cash for a complete rebuild on my engine, it has sat in a crate for the ten years since, but been turned by hand regularly and it was full of graphogen paste.
I have been gradually checking things over and running the engine up slowly checking things over as I go. I now have what I consider to be a significant amount of oil running down the left barrel fins, shining a light into the gap between barrel and head shows a few bubbles popping from the head gasket while the engine is idling. I cant see any leak around the rocker gasket seals which leads me to believe it is the head gasket. And if it is the head gasket, where is the oil likely to be coming from? The only oil way is the pushrod channel, correct?
As yet the engine has not been under any load, I run it up to warm, checking the fuelling, idling timing etc.
It is entirely possible the head bolts simply need a re-torque, or it might be something more serious.
As a start, does anybody have the correct torque settings ( or know where I can find them ) for a 1957 plunger engine. They don't seem to be in the Haynes manual.
If that fails then I am into a complete strip down, in which case I am going to be in a right grump. *smile*
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Could be coming from the front oil drain, there's one from each pocket in the head.
Torque to 30 foot pounds.
Trev.
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Hi Bassgreg, I had the same problem, and thought the gasket had blown. Silly me, it was solid copper, and in fair condition. How I wished I'd taken the advice of my mate next door and just torqued it down a bit. But he rides japanese bikes so I put myself through a few weeks of aggravation instead.
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started the old girl up ready for the MOT now its near after having it 5 years
Maybe I am reading this wrong but if its 1954 it does not need an MOT ?????????
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You're quite right, it doesn't, but I reckon it's worth the £30 to have a stranger look over it and spot all my deliberate mistakes.
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You need to tax it at a post office. And you need to fill out the MOT exemption form and show them.
https://www.gov.uk/government/publications/declaration-of-exemption-from-mot
Eric is right though, getting it thru one MOT isn't a bad idea.