BritBike Forum logo
BritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorBritBike Sponsor SteadfastCyclesBritBike SponsorBritBike SponsorBritBike SponsorBritBike SponsorHepolite PistonsBritBike Sponsor
Upgrade to: Gold Membership | Premium Membership | Vendor Membership | Site Sponsor Membership
Member Spotlight
rkinkade
rkinkade
Victoria, Texas
Posts: 267
Joined: November 2004
ShoutChat Box
Comment Guidelines: Do post respectful and insightful comments. Don't flame, hate, spam.
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Random Gallery photo
a word from..
Manuals on DVD (Shipping included)
Previous Thread
Next Thread
Print Thread
Rate Thread
B33, odd knocking only when cold ! (SOLVED)
#495624 06/27/13 3:15 pm
Joined: Aug 2012
Posts: 44
Britbike forum member
OP Offline
Britbike forum member
Joined: Aug 2012
Posts: 44
Hi all,

Now I am very familiar with the B33 type engines having had one for many years until I sold it, 20 years ago. I knew it right down to the crank shaft (if you see what I mean).

I got another one 2 months ago and am loving it again.

However, it does have an odd thing about it. Start it up from cold, let it tick over for a minute to get the oil moving. Then, when I accelerate away it makes quite a heavy knocking noise from the motor. The first time it did it I thought "Ah, I will be fitting a new crank or big end very soon" - But I then found that within 1/2 a mile, it stopped doing it I could then give it full throttle and it sounded fine. This has been the case with every journey. It will "re-do" it if I park it up for more than say 30 minutes.

I had considered a loose exhaust pipe to head, but it's not that.
I checked all mounting bolts (but that wouldn't change on warming up)
I wondered if the oil (it came with fitted) was too thick, so put 20/50 in.

It has an inline oil filter in the return pipe (mounted in the tool box), but I doubt that would be anything to do with it.


Any thoughts folks ?

John in the N.W. UK

Last edited by John Birkett; 09/11/14 3:38 am.

Current rides = 1959 650 Matchless G12CSR in near showroom nick, 1956 BSA B33 in "Goldy" trim (yeh, I know, cheesy but I like it !)
Support Your #1 BritBike Forum!

Check out British motorcycles for sale: British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Re: B33, odd knocking only when cold !
John Birkett #495634 06/27/13 4:34 pm
Joined: Dec 2004
Posts: 10,587
Likes: 20
Britbike forum member
Offline
Britbike forum member
Joined: Dec 2004
Posts: 10,587
Likes: 20
Piston slap ?

Re: B33, odd knocking only when cold !
John Birkett #495639 06/27/13 4:58 pm
Joined: Aug 2012
Posts: 44
Britbike forum member
OP Offline
Britbike forum member
Joined: Aug 2012
Posts: 44
Thanks for the input there smile

Sounds a bit "heavy" for piston slap, plus it blows no smoke and the comp is good, as is the plug colour. It really does "sound" like a hugely bad big end, but it can't be (can it ?) that would get worse if anything as the engine warmed up.

Odd one...


Current rides = 1959 650 Matchless G12CSR in near showroom nick, 1956 BSA B33 in "Goldy" trim (yeh, I know, cheesy but I like it !)
Re: B33, odd knocking only when cold !
John Birkett #495641 06/27/13 5:10 pm
Joined: Aug 2012
Posts: 44
Britbike forum member
OP Offline
Britbike forum member
Joined: Aug 2012
Posts: 44
Actually, thinking about it, you could well be right !

Can't really be anything else (that I can think of !)

Last edited by John Birkett; 06/27/13 5:11 pm.

Current rides = 1959 650 Matchless G12CSR in near showroom nick, 1956 BSA B33 in "Goldy" trim (yeh, I know, cheesy but I like it !)
Re: B33, odd knocking only when cold !
John Birkett #495652 06/27/13 6:56 pm
Joined: Dec 2004
Posts: 10,587
Likes: 20
Britbike forum member
Offline
Britbike forum member
Joined: Dec 2004
Posts: 10,587
Likes: 20
Piston slap will not affect compression, blow by etc if the rings are good, big ends going will get noisier as the engine heats up and worse under load.

Re: B33, odd knocking only when cold !
John Birkett #495664 06/27/13 8:19 pm
Joined: Aug 2001
Posts: 3,040
Likes: 8
Britbike forum member
Offline
Britbike forum member
Joined: Aug 2001
Posts: 3,040
Likes: 8
Could be piston slap, but it also almost sounds like the oil flow is not quite there when you start off. You changed to 20/50 like you say, no change.
Not quite being familiar with B33 oiling arangements, how does the oil get into the crank ? Could the seal (quill?) be not quite 100%. Once warmed a bit, the oil flow is sufficient. I once removed some 'fluff' from an oil line that was doing something similar.

Sounds like the reason it was for sale - the PO didn't figure it out either ?!

Re: B33, odd knocking only when cold !
John Birkett #495714 06/28/13 7:41 am
Joined: Jul 2009
Posts: 3,518
Likes: 1
In Remembrance
Offline
In Remembrance
Joined: Jul 2009
Posts: 3,518
Likes: 1
It could be that the small-end bush is too tight.When the piston heats up the pin can move more easily in the piston,but still doesn't move in the rod.

Re: B33, odd knocking only when cold !
Pete R - R.I.P. #495723 06/28/13 9:13 am
Joined: Aug 2012
Posts: 44
Britbike forum member
OP Offline
Britbike forum member
Joined: Aug 2012
Posts: 44
I did wonder about oil (which is why I mentioned the in line cartridge filter). These do use a quill on the timing cover, injecting oil up the centre of the crank. It all looks OK.

There is a decent flow from the return pipe in the tank straight away, with the usual bubbles (once the residual in the cartridge has cleared).

The bike is in a "touring Goldy" trim so this might be the ideal "reason" to get it re-bored and fit a higher comp piston (currently 7.5 :1) and some 2446 cams crazy

It already has had a re-con mag, a new Monobloc and a new exhaust shocked


Current rides = 1959 650 Matchless G12CSR in near showroom nick, 1956 BSA B33 in "Goldy" trim (yeh, I know, cheesy but I like it !)
Re: B33, odd knocking only when cold !
John Birkett #495730 06/28/13 10:34 am
Joined: Aug 2006
Posts: 194
Britbike forum member
Offline
Britbike forum member
Joined: Aug 2006
Posts: 194
Certainly not more likely than the other suggestions in your case, but this happened to me many years ago: When starting cold, one of the valve guides used to come loose and moved with the valve, up and down a short distance and making a strong noise. As temperature got higher, the guide settled and the noise went away.

Re: B33, odd knocking only when cold !
John Birkett #495736 06/28/13 12:10 pm
Joined: Aug 2012
Posts: 44
Britbike forum member
OP Offline
Britbike forum member
Joined: Aug 2012
Posts: 44
Interesting one Pelle crazy

Well worth adding to my (our) knowledge base smile

I reckon though this knocking sounds and feels heavier than a valve guide moving.

It even sounds a bit heavy for piston slap from my experience.

Hey ho, perhaps I should just wait and let the fault "mature" a bit laughing (or summat breaks crazy )

Last edited by John Birkett; 06/28/13 12:11 pm.

Current rides = 1959 650 Matchless G12CSR in near showroom nick, 1956 BSA B33 in "Goldy" trim (yeh, I know, cheesy but I like it !)
Re: B33, odd knocking only when cold ! (SOLVED)
John Birkett #562657 09/11/14 3:37 am
Joined: Aug 2012
Posts: 44
Britbike forum member
OP Offline
Britbike forum member
Joined: Aug 2012
Posts: 44
Came back on the forum to look for summat else and realised I had not done a "solved" on this one.

I feel a bit daft because it was such a silly thing. I was routinely checking tightness of various nuts and bolts and I almost idly checked the 4 head to case studs, yes they were no way near as tight as they should be blush Two of them (the front ones) needed about half a turn to feel correctly tight. Since doing that the knocking noise has gone and a good few hundred miles later all is good.

On a side note, the clearance on those hex flats to get a spanner in is a bit tight. What type of spanner dear reader do you use ? (I was considering getting one of those split ring type "pipe nut" ones ?)


Current rides = 1959 650 Matchless G12CSR in near showroom nick, 1956 BSA B33 in "Goldy" trim (yeh, I know, cheesy but I like it !)

Moderated by  Jon W. Whitley 

Link Copied to Clipboard
Home | Sponsors | Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons | DVD- Manuals & Parts books
Upgrade to: Gold Membership | Premium Membership | Vendor Membership | Site Sponsor Membership
Powered by UBB.threads™ PHP Forum Software 7.7.4