Push rod fail
- Thread starter freefly103
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I can't really see why the valve clearance being a few thou away from ideal would cause that to happen to the pushrod. I did have a pushrod break but it was caused by the valve sticking in the guide so the pushrod got dislodged from the rocker arm.
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Coil bound springs?
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Jim Schmidt of JS Motorsports included the information about setting the tappet clearance hot (one time) and checking it later when the engine is cold for a "cold tappet clearance reference number" to use with the JS2 cam I am using. I think my quote in the other post is accurate and I did say the technique was from JSM.
I set mine cold, which is what one would do after doing the hot set thing once.
I am not suggesting anyone do it with their stock Nortons or any version of Norton without talking to JS.
I didn't actually think very many VIP members would even see my post to be honest. I figured I was on a lot of ignore lists by now. lol
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Megacycle 1/4 race Cam.. radius followers ... 8 & 10 thou...
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OK.
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How hot is a "hot" (air cooled) engine?
Is a "hot" engine on a 95° F day the same temperature as a "hot" engine on a 65° F day? Has the bike been ridden in stop and go traffic or has it just come in from a liesurly ride on country roads.
A "cold" (ambient temperature) engine will not vary in temperature as much as a "hot" engine.
Water cooled engines are a lot more stable as coolant temperature can be controlled and monitored.
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Megacycle 1/4 race Cam.. radius followers ... 8 & 10 thou...
Become a VIP member today...or I will ignore you
I've got the JSM BSA lifter stuff in da engine, but with the little radiused Triumph lifters in the BSA lifter blocks instead of the slightly larger BSA lifters. The Triumph lifters were not my choice just what Jim sent me. They seem to be working OK now after I cleaned them up. The JS2 cam is somewhere between a 2S and PW3 performance wise, but with good put put torque. I have no idea what a 1/4 race cam is. Does that mean it's only good for 1/4 of a race?
My barrels are alloy so they grow a little more when hot than iron barrels. For grins I set all 4 corners to .006" cold today. Nothing was banging on anything it shoudn't be banging on. Motor was quieter though. I know one is supposed to use the manufacture's spec, but I outlined the JSM spec and it made more sense when I had iron barrels. With the alloy barrels the cold numbers end up too tight to my old fried brain using Jim's technique. Maney was specifying close to .000 in the OP's case.
I am just a parts changer.
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The reason I say quarter race is because I can't be bothered looking up the numbers...over the years I've used 2S... 4S... 7S....on both 750 & 850's..this one is better than all of them IMO for fast road use and nice BOOSTED mid range torque that they are born with...I've got the JSM BSA lifter stuff in da engine, but with the little radiused Triumph lifters in the BSA lifter blocks instead of the slightly larger BSA lifters. The Triumph lifters were not my choice just what Jim sent me. They seem to be working OK now after I cleaned them up. The JS2 cam is somewhere between a 2S and PW3 performance wise, but with good put put torque. I have no idea what a 1/4 race cam is. Does that mean it's only good for 1/4 of a race?
My barrels are alloy so they grow a little more when hot than iron barrels. For grins I set all 4 corners to .006" cold today. Nothing was banging on anything it shoudn't be banging on. Motor was quieter though. I know one is supposed to use the manufacture's spec, but I outlined the JSM spec and it made more sense when I had iron barrels. With the alloy barrels the cold numbers end up too tight to my old fried brain using Jim's technique. Maney was specifying close to .000 in the OP's case.
I am just a parts changer.
[Edit] I used the 7s and local cam doctor turn it into a 560 bla bla Megacycle profile...
I even found the receipt
You definitely need a VIP pass now mate !!
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Its best to use aluminum pushrods because they expand along with the cylinders. Steel pushrods don't so hot and cold tappet measurement changes dramatically. You don't have that problem with aluminum pushrods.
What happened to the engine, apart from damaged pushrods? Did you bend a valve stem as well? I hope the rhs piston survived. The pushrod's steel alloy may be nonmagnetic. How do you plan to locate and remove the steel fragments?
- Knut
A tappet clearance of 0.008" (cold) for an all alloy engine is excessive in my book. This will increase to 0.014" hot due to barrel and lower part of cylinder head being subjected to a higher temperature and therefore expanding more in height than pushrods and tappets do.
I think you should aim at a tappet clearance of 0.002" cold. This will render a positive tappet clearance throughout the temperature range. Personally, I would try an even smaller clearance of 0.001" cold. As always, engines should be heated up gradually.
A math experiment using a linear temperature distribution between crankcase/bottom of cylinder and cylinder head level at rockers shows that apart from small deviations in CTE for barrel, head and pushrod, the diminished clearance hot/cold can be projected very well. This makes me confident the cold tappet clearance may be reduced from 0.008" to at least 0.002" cold.
- Knut
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I reset them to go .006 no go .007 cold after I wrote that experiment thing up.
Jim's response up above indicated that the number should not have changed that much from hot to cold on my experiment using his adjustment technique given that I am using all the right alloy parts. He worded it in reverse mentioning steel pushrods but that is what I took away from his response.
It is possible that I screwed up on the measurement when it was cold. I'll have to do it again to be sure, because .002 is a mighty thin feeler gauge. The only time I've used a number that small on valve adjustment is when the valve train was all overhead roller on an Rotax thumper. Seems really small for an old Norton.
freefly103
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Knut, I removed the barrels so I could clean up the pushrod fragments that were sitting in the bottom of the tunnels. While they were off, I also checked for damage to the lifters and cam. Thankfully, there was none. I haven't removed the rh outlet valve yet, but do this and check if for a bent valve. Will change the oil and look for fragments in the magnetic sump plug.
freefly103
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Caught up with Steve this week. With standard alum pushrods, he recommends to halve the gap if using his alloy barrels i.e. 3" inlet and 4" outlet.
With his chrome moly steel pushrods, gaps should be set at 0".
I'm going to install a Combat head with his Stage 2 3mm oversize inlet valves, standard pushrods, standard cam and 80" copper gasket using the 3" inlet and 4" outlet gaps.
With his chrome moly steel pushrods, gaps should be set at 0".
I'm going to install a Combat head with his Stage 2 3mm oversize inlet valves, standard pushrods, standard cam and 80" copper gasket using the 3" inlet and 4" outlet gaps.
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This is a picture of the bottom of a page out of Jim's notes that suggest the hot tappet adjustment (last sentence). I know it is off topic and not about Maney parts, but wanted to provide more evidence for my virtual trial before the hanging takes place.
As I mentioned I'm setting them all currently cold at .006". Probably a little loose with my parts, but with the soft ramp JS2 cam it hasn't been an issue.
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I looked up the valve lift for this JS2 cam profile. It’s just a little less than a combat cam profile. Let us know what cold clearance you get.This is a picture of the bottom of a page out of Jim's notes that suggest the hot tappet adjustment (last sentence). I know it is off topic and not about Maney parts, but wanted to provide more evidence for my virtual trial before the hanging takes place.
As I mentioned I'm setting them all currently cold at .006". Probably a little loose with my parts, but with the soft ramp JS2 cam it hasn't been an issue.
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Sorry about quoting you, but I wanted to give my babble some context.
The JS2 has a linear power curve. Still has a lot of top end, but more torque down low. I had a SS cam in the engine previously, but the current engine is spinning less mass so hard to compare the cams unfortunately. Only thing I can say is I like the JS2 cam in this engine.
I'm going to do the number gathering bass akwards. I'm plan to start with a cold .006 adjustment and measure it hot when I return from a ride. Then set the tappets hot to .006 if they are not already at .006 hot, and check again cold. I may have too many different parts in my engine for it to mean much to anyone that doesn't have the same parts in their Norton engine.
Time to suit up and get with it.
Just got back from a combination in town and Hwy ride. It was a short 19 miles. Cold .006" exhaust ends up at .012" hot.
I'm not going to measure the intake side, because the engine has cooled some already. I figure intake is somewhere between .010 and .012. I'll have the hot .006" to cold exhaust number in 3 hours. I don't believe it myself, so I don't expect anyone else to believe it. I'll try Maney's alloy pushrod alloy barrel numbers cold and see if I break anything.
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.0014" cold on the exhaust this time. I'm going to use the same numbers for my cold tappet adjustments that were suggested by Mr. Maney and listed by freefly103 up above. Nortons are more fun than a barrel of monkeys.
