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Dommi top end disaster !

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Bike is a 1959 Dommi '99'. I bought this in the summer as a fully rebuilt working machine. When attempting to adjust the tappets I couldn't get the valve clearances adjusted correctly so I bought a new set of tappets. In trying to fit these it became apparent that the locking nut on the tappet would not fit above the rocker arm as it should. The tappet had to be wound so far through the rocker arm that there was no thread left for the lock nut. So, I fitted the locknut on the underside of the rocker arm. This troubled me. Why should this be necessary ? I decided to investigate so I've removed the head and barrel. This is what I've found:

All four push rods knackered. The top end of each is mutilated with bits of torn aluminium all over the place.

All four cam follower cups damaged, two beyond re using, although it may be prudent to renew all four.

Circlip missing from gudgeon pin on one piston. The gudgeon pin has slid into the bore and created a massive groove in what appears to be a liner. 

One piston (already +.040") damaged beyond repair.

The barrel has a piece of it's casting broken off at the base of the damaged bore. As this piece is not in the engine the barrel must have been installed in this state during the rebuild !

I'm now facing new liners, new pistons, new rings and new cam followers. I'm hopeful that all bits, especially the main piece of the dislodged circlip, have not and will not find their way into any bearings or gears within the crankcase. I've flushed it out to the best of my ability. 

My Questions:

1. What type of failure causes this type of damage to pushrods and cam followers ? 

2. Can I ignore the damage to the barrel casting and solve the problem with liners and new standard pistons ?

3. I am assuming damage to the bore is just due to the circlip either not being inserted properly or in it breaking ? More understandable than the push rod damage.

3. Is it safe to assume the missing piece of circlip has somehow been blown out through the exhaust system, or is it necessary to split the crankcase and search ?

4. Where  is the best place to go for the replacement parts ?

Mike Haworth

 

hello  manxman camshaft came out on november 7th 1960  not 1961  that the cast marking T2219 X1  camshaft The Norton 650cc Manxman came first Not the 650SS  witch came 9 months later on  as the british bikers like babys were scremming 650   by then  ,,,,  now you all stand corrected  And for your information I do welding of  cast iron   parts       along with other  engineering                                                                    yours anna j   

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Instead of making a new thread on camshafts. Just took out of a 1968 650SS Is this to be read as T2219@3

Cam stamping

 

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the pix shows the makers part # for the cam blank. it appears to be rev 3 of the mold/die.

22729  should measure out to a regular NHT twin chain SS cam. Assuming it has never been reground it should be around  1.219" tall. Same cam as atlas and twin chain commando.

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My understanding is that the SS 650 cam  opened a few degrees earlier and closed a few degrees later than the QR  , the lift may have been the same .I have the info somewhere .Certainly there is some discrepancy in the published data. Perhaps that comes about with the change in follower profile.

I only have one QR stamped cam from my 59 88 and the profile is posted on the above consolidated chart. The 22729 SS cam which is used on many twin chain motors is also posted. I measured real hardware and post the results that I find.  As in my graph, lift is NOT the same for QR and SS.

Not picking on you specifically but, don't believe me? Get someone with verniers to measure the whole lobe  and subtract the base circle to roughly get the lift. I have always been skeptical of people who just repeat/quote stuff.

When I can obtain, in my hand, and measure/test a daytona which is "rumored" to be almost identical to the QR  then I will finally believe that rumor too. The ramps should be the main difference and can be accurately measured and verified.

I have been trying to obtain a daytona cam for measurement . However parts like that are very rare here in north america along with people who know.

I will admit the exact opening and closing events for either cam may be as you say, but those are easily changeable with tuning hardware tricks. The full lift and in/ex lobe relationship is not changeable and is what I try to show on the graph..

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The Norton factory had massive quality control problems with all the timing gear they produced right from the very first Model 7 engine up to and including the early Commando versions. Timing pinions, camshaft sprockets and camshafts themselves were churned out with slight variations between each in terms of timing angles. When production moved to Plumstead/Woolwich this problem persisted but stamping the pinions with the timing differences ended.

The attachments show that originally pinions were measured up and stamped to show how much each varied from the required factory settings. 

People like Paul Dunstall made big money out of selling vernier kits that allowed optimum timing points to be realized in order to produce peak power. In his memoirs, John Hudson mentions that while carrying out serious warranty repairs on Nortons twins he often found that both valve and ignition timings were in need of correction.

The Graph posted by Dave Comeau illustrates very well how small changes to a camshaft profile can improve the power output of an engine. The change from round end  to flat end followers/lifters is something that can be done in any of the early twin engines and will boost power across the range by up to 10%.

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According to Mr Hudson,  the QR cam timing figures are 49/77/79/47  and the first SS cam is 50/74/82/42  both using 13thou checking clearance. Getting the inlet opening to lead the exhaust closing by8 degrees on the SS cam on both cylinders may need a little juggling with valve clearances, Doing the same on the QR cam may be a bit more challenging.

 


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