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C15F engine knock getting louder. #467255
12/11/12 6:59 pm
12/11/12 6:59 pm
Joined: Aug 2012
Posts: 65
UK
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BSA_pete Offline OP
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UK
My C15F (1965) ever since I bought this bike 6 months ago, has had a knock that I could hear, but others at the local BSA club, said they couln't and not to worry about it.

The knock is getting louder and due to the icy weather I haven't had chance to get over to the club, some 30 miles round trip away, for them to have another listen. Apart from that I really don't want to ride the bike with this knock.

I have made a video with sound (link below)

http://m.youtube.com/watch?feature=plcp&v=sJMzvkqNLho

so anyone willing can browse over to youtube and hear the noise I refer to. The video is really dark and crappy, for which I apologise, but its the noise coming from the engine that is the important bit.

Hoping somebody can advise me as I am really nervous about stripping the engine. This is all new territory for me.

Cheers.
Pete.

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Re: C15F engine knock getting louder. [Re: BSA_pete] #467264
12/11/12 7:16 pm
12/11/12 7:16 pm
Joined: Dec 2004
Posts: 9,436
Scotland
kommando Offline
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Sounds like a normal C15/Unit single clatter to me.

Grab a big screw driver and touch the engine with the pointy bit and stick the hangle to your ear, this will magnify the noises where the screwdriver touches, move it around until the knock is loudest and report back here what that is.

It may be big end but that is loudest under load not idling so probably something else like the alternator rotor etc.

Re: C15F engine knock getting louder. [Re: kommando] #467267
12/11/12 7:45 pm
12/11/12 7:45 pm
Joined: Aug 2012
Posts: 65
UK
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BSA_pete Offline OP
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Hi Kommando,

I did quickly try the screwdriver tip when I made the video. I couldn't hear the knock when I touched the primary case or the bottom of the barrel area, where they stamp the numbers, but at the rocker area I could hear a knock but not certain if its in sync with the knock.

The knock becomes really evident when you roll off the throttle after taking taking the engine up to half throttle. I'm hoping and praying it's piston slap or an upper end problem as I might have the bottle to attempt that repair myself. Just wish I could find somebody in the Manchester area who could help me, for a fee of course.

I'll try and make another video as the one I just made doesn't reveal the knock very well.

Cheers.
Pete.

Re: C15F engine knock getting louder. [Re: BSA_pete] #467271
12/11/12 8:26 pm
12/11/12 8:26 pm
Joined: Aug 2001
Posts: 7,509
scotland
triton thrasher Online content
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scotland


When the big end goes, you will be in no doubt something is wrong.

In the meantime, save your fee money. "Repair" piston slap on a Unit single? Don't make me laugh!

Just ride it and service it.


Amateur Loctite enthusiast.
Re: C15F engine knock getting louder. [Re: BSA_pete] #467893
12/15/12 10:24 pm
12/15/12 10:24 pm
Joined: Nov 2011
Posts: 126
Northern Ireland
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B31 Ally Offline
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Northern Ireland
BSA Pete, i watched your video and i only ever heard a noise like that on a C15 once and it turned out to be a small end in the conrod had got worn. Im not saying thats what is wrong with yours but the bike in question i worked at when you accelerated it was slightly quiter untill on the over run when you throttled back the noise was lethal as the piston was now hitting the head because there is no explosion of fuel and air to keep it pushed down. When i say hitting the head its only just hitting it but it can make sum racket.

Re: C15F engine knock getting louder. [Re: BSA_pete] #467896
12/15/12 10:39 pm
12/15/12 10:39 pm
Joined: Jul 2007
Posts: 529
Wollaston Northants
kelvin Offline
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kelvin  Offline
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Wollaston Northants
take it to Brian at Lighting Spares 170 Cross st Sale M337AQ Mon - Sat closed wed.

Re: C15F engine knock getting louder. [Re: BSA_pete] #467898
12/15/12 10:40 pm
12/15/12 10:40 pm
Joined: Aug 2001
Posts: 7,509
scotland
triton thrasher Online content
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scotland
The sound in the video is not decipherable as any engine fault. Just people muttering and some general mechanical engine noise.


Amateur Loctite enthusiast.
Re: C15F engine knock getting louder. [Re: BSA_pete] #467951
12/16/12 10:01 am
12/16/12 10:01 am
Joined: Sep 2004
Posts: 824
Farnham, Surrey, UK
gunner Online content
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gunner  Online Content
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Farnham, Surrey, UK
See this post on the B50 website Here where a guy had a B40 with a knocking sound. This may give you some pointers on what to check

Last edited by gunner; 12/16/12 10:20 am.

1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: C15F engine knock getting louder. [Re: BSA_pete] #467967
12/16/12 1:54 pm
12/16/12 1:54 pm
Joined: Aug 2012
Posts: 309
Hampshire, England
DoubleDiamond Offline
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Hampshire, England
If it were my C15 then I would take the head and barel off. This is a simple and straightforward job (it is on my '68 B25 which is essentially the same) and you can then answer your own questions by checking the little & big ends as well as the bore/piston clearance.

The weather is good for doing jobs like that (because its horrible out on the roads just now!) and you can then either put things back together or dismantle the engien to get done whatever needs doing: and you will be ready for the new season (assuming we get one!) early next year.

As ever, just my thoughts.....


BSA: '71 B175; '68 B25; '71 A65; '71 A75
Triumph: '87 T140; '72 T150v
Re: C15F engine knock getting louder. [Re: B31 Ally] #468482
12/19/12 7:29 pm
12/19/12 7:29 pm
Joined: Aug 2012
Posts: 65
UK
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BSA_pete Offline OP
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Hi B31Ally,

Sorry for the delay in answering but I've been really busy.

Thanks for checking out the video and you are spot on when you say the knock gets worse on the overrun. It's scary.

Using the screwdriver tip I can detect the knock at the upper head area. At the bottom of the barrel or crankcase I can't hear any knock. I would try removing the head but the 2 head nuts on the off side are awkward to get at. Do I need a special spanner to ensure I don't knacker them?

If the little end is going will there be bits in the crankcase which would mean a full engine strip down?

Cheers.
Pete.

Re: C15F engine knock getting louder. [Re: BSA_pete] #468525
12/20/12 2:10 am
12/20/12 2:10 am
Joined: Aug 2001
Posts: 1,137
Lucan ON Canada
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jfligg Offline
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Lucan ON Canada
Hello Pete
The fist thing you need to do is buy a service and parts manual. The only way you are going to find the problem is tear down part or all of the engine. If you don't feel confident there are some engine rebuilding dvds out there. They probably won't specifically be on the C15. But they will show you proper shop technics on engine rebuilding. Even try u-tube. Good Luck and keep us posted. Jeff

Re: C15F engine knock getting louder. [Re: BSA_pete] #468576
12/20/12 11:21 am
12/20/12 11:21 am
Joined: Dec 2004
Posts: 9,436
Scotland
kommando Offline
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Scotland
You need a whitworth ring spanner and it may need thinning to fit, opened spanners do not give enough arc and also come off the nut too easily rounding the nut. Have you checked the valve clearances, an adjuster nut may be coming undone.

Also a worn small end will not need a full strip to fix, a quick look in the sump will show what has been circulating.

Re: C15F engine knock getting louder. [Re: jfligg] #468778
12/21/12 10:22 pm
12/21/12 10:22 pm
Joined: Aug 2012
Posts: 65
UK
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BSA_pete Offline OP
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Thanks JFligg for your input. I shall search around for the DVDs etc and will let you all know how I got on.

Cheers.
Pete

Re: C15F engine knock getting louder. [Re: kommando] #468779
12/21/12 10:29 pm
12/21/12 10:29 pm
Joined: Aug 2012
Posts: 65
UK
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BSA_pete Offline OP
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Thanks Kommando,

I have open and socket Whitworth spanners so I'll have to check eBay for some
ring spanners.

Let you know how I get on.

Cheers.
Pete.

Re: C15F engine knock getting louder. [Re: BSA_pete] #468813
12/22/12 8:52 am
12/22/12 8:52 am
Joined: Dec 2004
Posts: 9,436
Scotland
kommando Offline
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Scotland
And I use combination spanners, spanners with rings on both ends mostly have a offset that stops it getting between the fins and the rockerbox underside.

Re: C15F engine knock getting louder. [Re: kommando] #468828
12/22/12 12:55 pm
12/22/12 12:55 pm
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Posts: 65
UK
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BSA_pete Offline OP
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Thanks for the valuable info.

Pete


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