Question-------------------------
Followup To
Question -
1974 Norton 850. The bike is altered with a megacycle 56 high performance cam. New stock pistons, valves, radiused lifters, racing springs, cylinders bored +20, balanced crank.
After the rebuild the exhaust pipe worked loose and a bunch of oil is in the exhaust. The ends of the muffler are oily and it puffs blue smoke from idle to 2500 rpm. The compression is 95psi cold and 105 psi warmed up. A shot of oil in the cylinder does not raise it much (5 psi)
One expert said rings were not seated, the other said maybe the oil is leaking from the valve guides and the compression is ok. I want the shop to do a leak down est before they get paid. That do you think?
Thanks
Answer -
Derek
I guess there a couple of questions still hanging in the air. You said it got new valves, but you didn't say anything about the guides. If these were not replaced along with the valves then there is the possibility the the new valves leave too much clearance in the guides and oil is being sucked into the combustion chamber on the intake stroke.
Is the compression same on both cylinders? The 850 is a lower compression design than the older 750's. I don't have the exact numbers. But they sound about right.
Is blue smoke coming from both? It is a valid assumption that the rings may not be fully seated, but this symptom should not last for long. It is also possible that the assembly lubricants have not burned off yet, but that depends on how much run time is on the engine now.
I can only hope the loose pipe is not the result of, or the cause of damage to the head. This could also be a possible source of the oil.
I guess the next question is why in the world would you want to have those performance enhancements installed on a classic machine which can do perfectly well what it was designed to do if maintained in stock trim. I know you don't want to race me and my Triumph Thunderbird Sport! You can easily outrun an old Bonneville or even a new Harley Sportster.
I would certainly begin negotiations with whoever did the work to make sure everything is right before you sign off and take your bike home. Having a job done sloppily and with questionable results is worse than not having the work done at all.
John
John,
Thank you for your reply. With all those other new parts, of course the valve guides are new. I was told that I measured the compression wrong because I did not open the throttle and had both plugs removed. The compression was equal on both sides. The smoke mostly from the left cylinder from idle to 2500 rpms. Very noticable and not right for a rebuild with 200 miles on it.
The shop is called British Marketing in Leguna Niguel, CA. It is under new ownership and the new owners have some lessons to learn about customer service. I hate to think what would become of them if they tried that back east. But this is California, the self service state. The Nortons have a threaded exhaust port and this machine has an insert pressed into the head to replace the stripped threads.
I insisted on having a leak down test performed. They prefered to tear the engine down again or they would not continue to work on the bike. I had no choice but to agree. This rebuild started in April. To answer you other question many of the 1974 Nortons had soft cams installed. A top end job became a complete rebuild when we took a look at the cam. These parts improve over what was there. Can you tell me a reason not to install electronic ignition, single Mikuni except for the joy or working on and pushing motorcycles?
Thanks again.
Derek
AnswerDerek
I have heard tales of the soft cams in Nortons, but have never had occasion to deal with one that died a natural death. Most of the worn cams I have seen have resulted from admitted abuse or neglect. But I can accept that after thirty years it could be worn badly enough to warrant replacement.
I guess you might think of me as a conservative or purist. That's why I refuse to alter stock configurations on any machine. I WILL use updated or improved pieces when possible.
The single Mikuni is OK to use as long as it provides the flow rate needed. The eletronic ignition is fine as long as nothing goes wrong. Then it might be the devil to diagnose.
Don't toss away the old carbs or points, etc. Keep them available. Should you decide to sell your bike the original parts will enhance its value a little bit.
There are a number or Norton owners associations all across the country and even in California. Do a web search and contact your local club. They can provide valuable references as to the best local shops and parts availability.
John
