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#1 |
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Join Date: May 2012
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I am helping a friend with an engine which has too much clearance between timing gear and cam gear. A used DanM aluminum cam gear was on there, which seemed a bit beat up from being run loose on another motor, so I just now swapped it for a brand new DanM bronze gear.
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'31 180A Last edited by tbirdtbird; 02-03-2017 at 10:35 AM. |
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#2 |
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There used to be oversize cam gears to help these conditions. I don't know if you can find any tho.
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#3 |
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yep, looking for input before we order one from Dan...
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'31 180A |
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#4 |
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Sounds like the babbitt job is ruined. You can put a .005 over gear on the cam but it will only close the clearance about .003 overall. If the babbitt is wearing like you say it will go south pretty fast and might take some other important parts with it.
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#5 |
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I'm gonna think on this a bit but I kinda agree with Mike. My first thought are I would think that a loose gear lash would not run as hot as one without enough lash. Maybe that is not the case?? I'm not sure the noise is totally gear lash. How did they do on setting the crankshaft thrust?
I have a Kwik-Way line Boring machine with the fixtures that align off of one main bolt on each end. Mike Rogers has the same basic machine as I do. I don't know what everyone else uses to locate their boring bars but for me I would see if there was enough shims where I could remove .002"-.004" worth of shims and re-line bore it. I'm thinking it may mostly take the babbit out of the block and just true-up the babbitt in the caps. Again, I would want to think this one thru a little bit more. In the interim, can you give us a mic reading on all three sets of main shims to see what you have? |
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#6 |
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'31 180A Last edited by tbirdtbird; 02-03-2017 at 10:35 AM. |
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#7 |
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Brent, the only thing apart right now is the timing cover is off
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'31 180A Last edited by tbirdtbird; 02-03-2017 at 10:36 AM. |
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#8 |
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What are you going to do if the crank is not on a parallel center line. If the crank is in the right location on the rear bearing. You are going to have some connecting rods moving all over the place. They will be trying to push the wrist pins out,and hitting the piston pin bosses. If the guy was that far off I would not trust the rest of his work.
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#9 |
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All align boring bars will bore at an angle
(IF). The bushings are bad in a Tobin-Arp, to loose, or both arms are not in the same alignment. If the boring frame type align bore bars have bearings wore out, or excess clearance. There are alot of shops using wore out tooling. |
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#10 |
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OK, I have had a communication from Dan McEachern
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'31 180A Last edited by tbirdtbird; 02-03-2017 at 10:36 AM. |
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#11 |
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I cannot help but think this may go deeper than just excessive lash. Since I have not knowingly experienced this, my guess is if the journals are line bored at an angle, there would/will be all kinds of other vibration and harmonics issues. Theoretically the rods are located differently in relation to the piston bores, and the flywheel would not be parallel with the flywheel housing thus creating a transmission input shaft issue.
I guess the real question is how much will it really affect the operation and longevity? Yes, we all agree it is not correct and none of us would want to be guilty of putting out that craftsmanship, however on the flip side, surely there have been shops in the day that did the same thing. Are some hobbyists unknowingly driving Model-As with engines that are mis-linebored?? |
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#12 |
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tbird what was the history before you got involved in this motor. from your post that it is basically assembled and in the car was it a whining problem from the gears?
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#13 |
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Though I never heard it, it was described as whining and then some.
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'31 180A Last edited by tbirdtbird; 02-03-2017 at 10:37 AM. |
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#14 |
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Crankshaft gears can look good and still be undersize. They can wear so evenly, that unless you measure the tooth width you will not suspect it as the cause of excess backlash.
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There seems to be an ASSUMPTION in this thread, and we all know what that leads to. The assumption is that all steel crank gears have the same pitch diameter, and they DO NOT. I have a number of used crank gears that have probably seen 100,000 miles grinding against dirt impregnated fiber gears. The pitch diameter has been severely reduced, and they would rattle like crazy against even a 0.005 over cam gear. One of them has so much tooth width worn away you could use it for a chain sprocket.
If this engine was put together with a well-worn crank gear that may be the problem, not the CL-CL distance. |
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#16 |
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I believe #15 and #16 are possible.
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'31 180A Last edited by tbirdtbird; 02-03-2017 at 10:37 AM. |
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#17 |
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I had an engine once with a C to C variance of .007 beyond std. Dan made me two gears that meshed beautifully, one being oversized to correct for the .007, and the engine is now quiet and runs smoother, too. (You should replace gears in sets, if you were not planning on that in the first place.) Dan is da man for this. I can't see the rest of your engine so I have no opinion on it other than if some work was sloppy, I would suspect there is slop in other places.
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#18 | |
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#19 |
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There is not a one align bore machine that will line up on any one block and get the center distance right.
You can be Plus or minus .010 off. You have to treat each block by its self to set center distance. You can,t just use a centering Jig that came with the Align Bore machine and expect it to come out right, it doesn't work that way. Herm. |
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#20 | |
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![]() When meshed against a new bronze cam gear I have (unknown actual variance from standard) a new crank gear vs. the most worn one in my box of junk, the cl-cl distance varies ~ 0.012 BUT, and this is a big "but", at that point the new cam gear I have on hand bottoms out at the root of only the worn gear, AND there is still play, because the wear is uneven and only on the thrust face of the teeth. This may be a function of an excessive addendum on the cam gear, or insufficient dedendum on that particular crank gear. Although those figures can be looked up in a machinery handbook and calculated, I have no way to measure it, as their datum point is relative to the pitch diameter. It's a vicious circle. Literally. Basicly, a worn thrust face on the teeth makes the actual pitch diameter a false indication of running clearance. Even if a special 'fat tooth' (way over-pitch dia.) gear were made to restore backlash to near zero with a badly worn mate, the compromised thrust face geometry on the worn gear would wear out the new gear in short order. |
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