CS1 Cam Failure

Previously Ian MacDougall wrote:

Today I've been helping my brother-in-law with his 1936 CS1 which had suddenly become worryingly noisy at the top end. We quickly worked out that the inlet valve was shutting with a bang, definitely not following a cam profile. We removed the cam box side cover and discovered swarf in the cam tunnel. One piece was big enough to be identified as a small section of the periphery of a cam, with the vernier peg holes visible. End result is that the inlet cam is no longer positively connected to the exhaust cam, the inlet can be rotated a few degrees relative to the exhaust. On closer inspection of the cams (still in situ) it looks like the damage is on the exhaust cam.So we know what is wrong, and have identified at least 2 possible suppliers of replacement cams (Paul Norman, Ian Bennett). Some questions remain: has anyone else experienced this sort of cam failure? If so was any conclusion reached as to why it had failed? Lastly, should we concerned about possible damage to the head of the inlet valve caused by the uncontrolled rapid closures?

Cheers, Ian McD

I think your suggesting thepeghasbrokentheexhast camcasting and thetwocamsarenot pinnedtogether but moveabout thedistance of thedamageand remaining pegsize? Ivehad halfadozenCammy Nortons andnot experiencedthat issue. Otherpetentialdamagecould bethe camtunnel itselfif the tappetis fallinginto a voidinstead of thecam surface. Theinner arm of therockercould potentiallytouch thecamtunnelandbreak it down.

Seatandvalvehead wise, itsdependanton howlong itran like this. I think thestresseswould be similartorunning into valvebounceso i doubt itsgoing topop off,(AsIremember thecoilspringratewasnothigh). Butfor thepriceofa valveitsworthchanging anywayisnt it?.

Withdebrisin the innersanctum itsacamboxrebuildanywayright? Your suggested suppliers are good, though cams arefairly regularyput up onebay. Stu Rogers over at Wisbech wouldprobablyholdthem in stock also (and valves).

Hope itsnot too badlybruised.

Cheers

Jon

Previously Ian MacDougall wrote:

Hi Jon, thanks for your comments. I don't believe the engine was run for long in this state, just to the end of the street and back. As soon as the noise started my brother-in-law realised that something needed attention!

At first inspection, with the camshaft still in place, the tunnel does not appear to have suffered. The inlet cam is still present so the rocker would not have dropped into a void.

At the very least we will remove the camshaft and make sure that any remaining debris is cleaned out. This cambox is reasonably oil tight so would be reluctant to disturb any more than necessary.

Assuming that the peg is now effectively working in a slot rather than a single hole I think this is what was happening: As the inlet cam started to open the valve it was pushed hard one way against the exhaust cam. Once the lobe had passed over the end of the rocker spring pressure would be acting in the opposite direction, pushing the inlet cam back to the opposite end of the "slot" in the exhaust cam. In effect the closing ramp of the cam was skipped over.

Comparison with valve bounce is probably valid, but it would be a sensible precaution to change the valve(s).

A friend here has come up with a pair of cams (originally supplied by Stu Rogers) which we believe are CS1 profiles rather than Inter, and offered the loan of a jig to hold the cambox. At this point we think we have got off lightly, but need a closer inspection to be sure.

Given the racing miles that this type of engine has done it does seem like an unusual failure. Would still like to know why.

Cheers, Ian McD

I'm with you on disturbing anoiltightcambox, just try and retrieve all themissingbits. With theshaft comingoutforreplacementcams justcheckthe key issecure in theshaft slot they arerathersmall andany movementtheremay translate to thethemovementwhich causedthevernier pin to break out.

Nice machines, CarollCS1's

Jon

Previously Ian MacDougall wrote:

A magnet has been suggested to help retrieve all the swarf. While the cambox is off we should also look at the vertical shaft bearings to see if any of the debris has ended up there. If we do find evidence that the swarf has travelled then we may need to dig deeper, wouldn't like any of that stuff to go through the pump.

Cams & cambox jig collected today. That required a round trip of around 130 miles on the 19S. Great excuse for a run out on a perfect biking day!

I have to agree with you about Caroll CS1s, but then I am biased having run a '37 model for around 12 years now. PO fitted an Inter top end, TT carb & BSA front wheel (decent brake) to mine, while the one that has just suffered the cam failure has a swing arm conversion and hydraulic suspension unit in the girder forks both done sometime in the 50s.

Ian McD

Both sound interesting machines. A 130mile round trip ona classic inthisweathersoundsbliss.Therouteback to thebevel drives is quite limited justlifting thenutsandslide thecoverup/downwill reveal thestrainers andcolection of debris. Thestrainer boltbelow thelowerbevelmay beremoved(Notsure ifa34hadone?).

Picture of twoof theswing arm andhydrauliucwould be of interest.

Cheers andgood luck.

Jon

I had a pin shear off in the cambox once. The nut that holds the bevel gear to the camshaft came loose, putting all the load on the pin that does the vernier adjustment and it broke. Is it possible this happened with the nut that holds the two cams on the shaft coming loose? This would allow everything to rattle and maybe break out the side of the cam.

I bought cams (and lots of other bits) from Ian Bennett for mine and am very happy with the quality of all his parts. Have had a lot of other parts from Stu Rogers and Paul Norman and would equally recommend either of them.

Good luck with it

Andy

George Cohen's notes on camshaft nut tightening procedure are well worth reading. I came up with a stabilizing fixture improvement using a 7/16" square drive socket that makes this a bit easier and safer. As George recommended, tighten nut to nut, not against shaft end.

https://drive.google.com/file/d/0B_5ev0g65Xk6cnNzTlFsTzVUWGM/view?usp=sharing

He suggests tightening the higher torque nut first, gear end, and then the other. Should work. Mind you, I haven't actually tried this. You can't get a torque wrench on the small end while it's in the jig but if you scribe the gear end after it's torqued, you can lock up the other nut with a wrench and then use a torque wrench backwards on the gear end, then checking your scribe. See here for torquing gear nut:

http://www.vintagenorton.com/search?q=camshaft+torque

-Mike