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Discussion in 'Airheads' started by RGregor, Dec 24, 2012.
Thanks, I'll try that.
Something worth considering about pushrod rigidity is the diameter and material modulus of elasticity. In the sport of archery (which is completely unrelated) aluminum arrows have been merged with carbon fiber to form a composite shaft. This allows smaller diameter, lighter arrows, that have the same stiffness as arrows made from aluminum of larger diameters due to the increase in material modulus.
As such, a (slightly) larger diameter pushrod made from aluminum-carbon composite will be stiffer than a standard aluminum tube without much of a weight penalty. I am not sure about the thermal expansion because of the carbon layer, but the length change will be closer to aluminum than pure carbon. I have to expect the 'state of the art' pushrod engine racers have looked into this material and it's just a matter of searching for the right keywords.
From what I have read, the state of the art pushrod guys (NASCAR, NHRA, and Sprint car) are for the most part using 4130 with a small minority using 4140 if I remember right.
I was just thinking about one of my aviation bosses. He liked 1025 a lot for maybe something like this but I don't know if its available right now. There is a California pushrod maker (can't remember the brand name right now) that use to make them for the guys at B+S and whatnot with 1018. They make a lot of them out of 1018. I would prefer 1020. Personally, I like the way it machines much better than 1018! I had mine made out of 4130. It takes compression quite a bit better than 1018.
Actually..... you can use one on a /5. switch to a crank ignition, block the cam hole in the cover, replace the oil pump with a later version. The double row cam gear fits perfectly on the bean can cam. I did all this on my early model /6. Also...on a /5 you need to clearance the inside of the block around the bottom end of the lifters. I placed my 336 inside a /5 block and found that the lobes connected with the block in this region by just a small amount.
Yet another observation, not related to engines, is that bicycle frames made from 4130 chrome steel can be made nearly as light as those from aluminum tubing because the 4130 wall thickness can be reduced. The thinner walled 4130 tubing compensates for the thicker wall needed for the aluminum frame due to the increased strength of 4130.
When needing more strength, such as for a stiffer pushrod, a larger diameter tube (which may not be practical), thicker wall, or higher strength material are required. So, unless the material can be lighter and/or stronger but heavier, a weight penalty happens. No one may have yet tried the carbon fiber/aluminum composite materials - or there may be some other problems such as attachment or fatigue with the composite.
Edit: I received my 336 cam from Max BMW. It was shipped in the yellow plastic bag. It's not the prettiest cam I have ever seen and the lobes are not polished but they have a taper.
I bought one of the 336 cams that were on sale at Max, and mounted it in the lathe to take measurements, here's the set up:
Measuring from right to left (ie,from rear to front) on the cam:
First, I spun the cam to determine the point on the lobe that was the "peak". At that point, I then traversed the DTI, to get the relative height difference across the face. I wont take up bandwidth showing each lobe, you get the idea, here are the compiled measurements:
So, two lobes with taper, two without. A paperweight, refund or exchange time, right?
I got one of the 336 cams from Max and it appears ok. I haven't gotten out my micrometer, but my digital vernier shows ~.003" relative taper. By relative taper, I mean measured from the lowest cam point to highest. I haven't put mine in the lathe yet.
There are several shops that can grind a taper on the cam. Volkswagon speed shops come to mind: (http://www.mofoco.com/category/VW_Camshafts_Cam_Parts/c134). That is what I had planned to do. I still plan to send out a replacement set of lifters and have them re-ground. For the adventurous, a tool post grinder on the lathe can be used for the taper rather than sending the cam to a shop. Or, send the cam back for a refund and abandon installing the 336.
Guess what ? Moorefield was right.
About 50000 miles after being fitted in the engine that's how my 336 and right side followers looks like :
Left side shows a normal wear for the mileage, and absolutely no pitting or unusual marks.
After taking measurement, there's indeed no tapper on the right side lobes. It seems obvious that there's a direct relation between that and the wear.
Will see how BMW will deal with that...
Thats a real bore, hopefully BNW will help you out, people fitting 336 cams to their client's bikes must expect trouble in the months ahead.
Awesome! Now we have the issue duplicated and verified. I wonder if all the new cams ground like that or just some of them? Man I am glad I saved one of a batch I got years back. I thought they might stop making them and they are an awesome cam. I wonder if the bad ones really are made in China? I am absolutely sure even German cam manufacturers can make a bad batch of cams!
Richie was hardly going to stand up and say they were wrong unless they really were... Despite Supershafts best attempts to shoot him down
I don't think it is the people who make the cams... it the firm who grinds/shapes them. Nonetheless... they do seem to be crap.
Would you stop the BS Rob. Shoot him down? Give me a break! We only had one source on the issue. Then two but we didn't know if that source was just repeating the first source's story or not. Science is all about repeatable results. Now we have repeatable results. Don't turn it into a personal pissing contest when it never really was.
We still only have one source on them being made in China. It that verifiable? Are the blanks made in China too? Or are they just ground in China?
Well... I do not give a fuck if they are made in China, Germany or anywhere else. That's not the point. The point is that they are piece of shit.
I wish that were true to me! Unfortunately I have seen a LOT of crap made in China. I know they can make it right. I just rarely see it and I don't want to have to buck the odds.