Author Topic: A small rattle in the engine department....  (Read 2140 times)

Offline Guy Wilson

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A small rattle in the engine department....
« on: 14.09. 2015 18:38 »
During a ride at the weekend through the tea fields of Limuru, just north of Nairobi, a horrible rattle bought the bike to a halt faster than the front break ever could...
Initially I thought the dynamo chain had broken, when this was interacted, I though maybe its dropped a valve guide. Finally I thought, shouldn't those pistons be at the same height?
barrels off tomorrow. Its a mechanical 'pass the parcel' what will I find when I take the next bit off?

Online bsa-bill

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Re: A small rattle in the engine department....
« Reply #1 on: 14.09. 2015 19:05 »
if the pistons are a pair that would be a yes then, so little end, big end maybe, timing side bush I think would have caused havoc before it got that much play, it will be interesting to see :(
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online Greybeard

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Re: A small rattle in the engine department....
« Reply #2 on: 14.09. 2015 19:06 »
 *sad2*

Online RichardL

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Re: A small rattle in the engine department....
« Reply #3 on: 14.09. 2015 19:57 »
A small rattle?

A few things I can guess at with little chance of being right.

1. We've seen a mod here on the forum where the crank was modified for, I think, 180 degree alternating up and down strokes between bores. I doubt that's what's going on here, so I'm not going looking for that topic to expand on the details.

2. Little end broke right next to the gudgeon pin letting one piston stay up while the rest of the rod rides up and down in the bore and, at the same time,  the other cylinder keeps running to propel the bike. (Talking to self: "But Richard, wouldn't the broken rod ultimately push the piston at least to the top of its stroke?") 

3. Piston fractured circumferentially at one of the ring grooves with same result (and same talking to self).

4. Broken crank?

If  a rod cap came off, the devastation to the crankcase would not be subtle.

I should just stop because, in fact, I really don't get this if the engine was still capable of running before disassembly.

Very anxious to see the truth.

Richard L.
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Online bsa-bill

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Re: A small rattle in the engine department....
« Reply #4 on: 14.09. 2015 20:42 »
Expanding on the possible but not probable scenarios, you have A65 con rod on one side, doesn't explain the rattle but might push you to get the barrels off and put the rest of us out of our misery  *smile*
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline muskrat

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Re: A small rattle in the engine department....
« Reply #5 on: 14.09. 2015 20:52 »
Oh bugga.
I'd say rod snapped at big end or snapped crank. Time to look for a large journal crank & rods. *sad*
Cheers
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Offline chaterlea25

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Re: A small rattle in the engine department....
« Reply #6 on: 14.09. 2015 21:13 »
Hi,
 
BSF

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Offline Guy Wilson

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Re: A small rattle in the engine department....
« Reply #7 on: 15.09. 2015 05:19 »
ahmm...my tongue was very firmly in my cheek about the piston position. I've rebuilt / reassembled this engine's top end from the barrels up, so I do get the consequences of the piston positions. The engine is relatively low mileage, 20,000 or so but had only done about 50 miles since being put back together.

We'd been riding of about an hour an never exceeded 50mph. We were riding up a gentle hill, two up when this happened. There was no warning other than the engine appeared not to be pulling as strongly as it was, no unusual engine noise at least.  I put that down to the hill, two up and the 7000ft altitude. I had the clutch in almost immediately It made the noise, and coasted to a stop. It really did sound like the dynamo chain had broken and I was kicking myself because I didn't have an allen key to remove the timing case. if I had, I'd fully expected to be able to remove the chain and ride on.
When the chain was fine, I thought a valve guide or seat had dropped. It really didn't sound as serious as it obviously now is....
I'll pull the barrels off after work today and see what the real damage is.

More updates as I have them...

Thanks again for your thoughts. I'll have some serious and specific questions soon!

Guy

Offline Guy Wilson

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Re: A small rattle in the engine department....
« Reply #8 on: 15.09. 2015 06:33 »
In responce to Richard's query. As soon a the 'rattle' started, I pulled the clutch in and coasted to a halt without the engine running. The picture of me looking at the engine is poetic license...The only noise at that point was 'how are we going to get home now?' from the photographer...
Guy

Offline WozzA

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Re: A small rattle in the engine department....
« Reply #9 on: 15.09. 2015 06:49 »
OUCH...  I bet you said a lot of IN & OUT words when you pulled the head off..   *doh*
good luck with what you find & the rebuild..  *wink2*
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Online bsa-bill

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Re: A small rattle in the engine department....
« Reply #10 on: 15.09. 2015 08:34 »
think I need my eyes tested again, I had not noticed the actual pistons in the pic, I was looking at the marks at the top of the bore left by the top ring which do look different but but no where near as bad as it is, hence my A65 remark.
If the marks I was looking at (top of the bore) are correct and not a camera angle thing then something has been out of place for a while and maybe not a sudden failure altogether,
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

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Re: A small rattle in the engine department....
« Reply #11 on: 15.09. 2015 08:53 »

 Sorry, but I'm a bit short on envy for you... *cry*...when I busted a crank, it ran fine but had a rumble and a bad vibration (think earthquake)...

 I'm inclined to go with a dropped cap from the right hand rod bigend

 Not happy for you, hope it's not too bad good luck
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
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Offline Guy Wilson

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Re: A small rattle in the engine department....
« Reply #12 on: 15.09. 2015 09:09 »
let me pull the barrels off and maybe all will be revealed....Whatever the case, I've got to split the crankcase. I didn't split the crank when I rebuilt it as it seemed fine...'experience is what you generally  get just after you need it..' as my friend Charlie says..
Guy

Offline Guy Wilson

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Re: A small rattle in the engine department....
« Reply #13 on: 15.09. 2015 09:11 »
yes it sounded more like a sudden failure. Certainly no earthquakes, it was more like an old alarm clock going off,
Guy

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Re: A small rattle in the engine department....
« Reply #14 on: 15.09. 2015 09:24 »

 I guess a wayward rod cap would be a progressive thing though, something you'd notice
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia