I simply cannot get it through my head how it's possible to place the cam gear on the shaft in 2 different positions (one being 180 deg. out) and still have the engine run in either position. One has to be wrong. With every modern I've done placement of the cam & crank gears was not optional. The went on their respective shafts in one position only. Usually with a keyway arrangement. I've never done this job on a T and I'm only looking at the Mac's catalog picture which seems to show that the shaft would have to be rotated if the marks didn't align & the gear was 180 out. Starting from scratch say (new shaft & gear) how can putting the gear on 180 out result in a running engine?
I'm with you Charlie, I've been scratching my head on this one since I read the thread related to the cam gear. I have a motor down right now and I'm going to look this cam gear over today. Always something to learn. PK
I'm thinking perhaps your setting, for instance, #1 piston at TDC (compression) or the top of the exhaust stroke. That makes some sense to me and I think the placement of the timer roller would coincide also. Am I getting close?
If you think about it, one would think that you would have to put the cam gear on in only one position to put the lobs in the correct place. For what ever reason you don't need to do that with the Model T, it works in two places. You could turn the cam gear 180 degs and the engine will still work as well. The simple answer is, you match the marks on the gears and you are done.
(Message edited by redmodelt on October 25, 2015)
The crankshaft makes two complete revolutions for each revolution of the cam shaft. For that reason there is no way to install the camshaft 180 degrees out of synch, or any multiple of 180 degrees. One complete turn of the camshaft is 360 degrees.
This is true of any 4 cycle internal combustion engine.
Model T camshaft / crankshaft gear alignment marks are not in synch with top dead center of any piston. This confuses people for some reason.
Just using #1 as an example. Trying to find the reason it works with the gear in either position. Believe the reason is as I stated above that you're just putting the entire engine at a 180 degrees one way or the other. At TDC (compression) or TDC on the exhaust stroke. It's the only way I can think of where it would work. Since the timer roller (usually) would also be 180 out (and there fore correct) the engine would run. Discounting the shafts that are drilled clean through where you'd have to change the roller's position if the timing was off because you installed the roller wrong. The engine doesn't know the difference. Every thing is OK just in a 180 deg. different configuration.
"How can putting the gear on 180 out result in a running engine?"
Because the locating holes are 180º apart, when you put the camshaft gear on, one way or the other, you're not changing the camshaft position in relation to the crankshaft.
According to the Mac's picture the gear can be installed 2 ways. One way is "normal" the other is 180 out. It will also work that way because the engine is now 180 out. The timer roller is also 180 out making every thing OK. A bit hard to fathom but I believe that's the explanation for it running in either position.
If you were to put another mark on the camshaft 180 degrees opposite the existing mark, then rotate the crankshaft all the way around so that the mark lines up with the other mark on the camshaft, you would see that either position of the camshaft gear on the camshaft would line up with the crankshaft gear.
You're missing the point. Forget about another mark you don't need one and it confuses the issue. Let me try this again: First, you have a camshaft gear that can be installed CORRECTLY in 2 positions. Lets call them North and South. You have the #1 piston at TDC. The marks will align at this point. You put the cam in one way (north) and the piston is set for compression. You put the can in 180 deg. (south) out and it's set for the top of the exhaust stroke. Cabish? It will work either way.
Charlie, You are right. And as you said you need to move the roller 180 to make it work. scott
It's the only possible explanation Scott. Actually the roller (the ones that can only be installed one way w/out the thru-hole)) will also be correct no matter which way the shaft is installed. With the crank set so it's timing mark will align with the cam gears marks you either set it up for TDC compression or TDC top of exhaust stroke depending on which way the gear ends up on the cam shaft. Every one that's done it says they work/it runs no matter which way it's installed. This has to be why.
The commutator is held by a pin which inserts into the camshaft in just ONE position as the hole should not go through. So whichever piston (1 or 4) is at the top, the correct coil will be fired.
So when you think about the position of the camshaft in relation to the crankshaft, you MUST remember the relationship of the commutator.
You don't move the roller 180 out to make it work, as the roller can only go on one way in the later cams, it always right timing with the cam either way, line the marks and #1 is firing, turn 180 degrees and then #4 is firing, roll it around back to the marks and it's firing #1 etc.
On the whole set up the only way you can be 180degrees out is to have the early cam, about the first 4,000,000 or so, that has the roller locating pin hole drilled through, that gives you 2 ways to fit the roller, even with the timing marks lined you can be 180 out and no running engine!
Charlie, If you can only install the commutator in one way then you can only install the cam one way. You can not change the cam lobes by 180 and leave the commutator in the same position . Just cause its in print from Mac,s doesent make it true. Scott
As I said in my last post: the timing roller will be correct. The only way it could be wrong is with the earlier shafts with a drilled clean through roller pin locator hole. You can install the roller wrong with that type shaft. Repeat: every one that's done the job says the cam gears placement on the shaft doesn't matter it'll run either way. You put the cam in 180 out and the roller is in a different position too. It's got nothing to do with Mac's picture being right or wrong.
Actually, you are not putting the cam out by 180 degrees, only the gear is off that much and it doesn't matter. The cam gear is not used for anything but to connect the cam to the crank. It doesn't matter which way it is aligned as long as the marks line up when they pass each other.
Thank Goodness this is finally settled. Now, if we can only get people to understand how a differential works and that neither axle is more inclined to turn than the other and the transmission brake is not ONE WHEEL braking.
You are SOOOOO correct about the differential thing!!!
The competition did a pretty good job explaining the differential in this 1937 short:
James it does matter which way the cam is set and you can install it 180 deg. out. It can't be set in any old position & can only be installed in 1 of 2 ways. Both correct as it'll run in either position. You install the gear on the shaft. It's either in the original position on the shaft or it's 180 deg. out. The marks obviously have to align. It'll run and the roller would be correct too. I know this is a tough one for the shade tree boys but if you know engines you'll know what I'm talking about PLUS we know it works from previous posts..
You get right down to it, a cam is "180 degrees out" every other revolution of the crank shaft. For you guys that think your cam is out by 180 degrees, just turn the engine one complete revolution and your cam will be right back where you think it was supposed to be. And when you get it where you think it is supposed to be, turn the engine one complete revolution and your cam will now be "180 degrees out". The cam turns EXACTLY 1/2 turn for every full turn of the crankshaft. 180 degrees is EXACTLY 1/2 turn. A piston doesn't care whether it's coming up on compression of coming up on exhaust. It just knows it's coming up. The position of the cam is the only difference between compression and exhaust.
The problem comes in when the cam is drilled all the way through and the timer roller/brush/Hall Effect flag is 180 degrees out from the rest of the cam. THAT is a problem, but is has nothing to do with the cam gear.
I don't mean that you need to put another mark on the gear. I just used it to explain why the existing mark can be used without any problem. You see with two rotations of the crankshaft to one rotation of the camshaft, both marks would align if you were to put another mark 180 degrees on the gear. No need to put another mark, because the gear will be properly aligned either way.
Listen guys: forget about the cam/crank rotation. We're talking about setting the cam correctly in the engine. A cam is not and will never be 180 deg. out if it's installed correctly and the engine runs. You're missing the point and that's correct installation. Period. As to adding another mark to the gear exactly opposite the original one? Guess what? you're just doing the same think as re installing the gear in the opposite direction you had it. Put another mark on it in directly opposite to the original mark AND USE EITHER MARK. It'll run.
I think ura preachin' to the choir.
Charlie is correct! I liken this to when people I build motors for call and ask why the #1 piston is not at the top when the marks line up. Some things you just can't explain to some people.
It's very tough to fathom. I get it. I honestly don't know if the #1 piston is at TDC when the marks are aligned and it won't matter if it isn't as long as the marks align. Just using that to try to explain that the shaft & gear can be installed 2 ways correctly.
I tried to explain this to a fellow today and he couldn't figure either out LOOKING at it. The piston won't be at TDC when the marks align because the cam is offset to the centerline of the crank and piston/rod.
So witch way I got lost half way reading the posts
So if you just line up the marks cam and crank and install worst case is I just change wiring on my timer shoot been to long
Might be best say lobe#1 intake faces this way if correct
bob, you don't need to rewire the timer! The crankshaft doesn't care if it is top dead center on exhaust stroke or top dead center on compression stroke! As long as the marks line up on the gears, the timer will always be the same because the valves and the timer follow the camshaft rather than the crankshaft.
This has been a fun thread!
This thread got me thinking dangerous for me last weekend I just put in my cam lined the marks and moved on but after reading this post kinda got worried on my rebiulders only been 15 years or so since my last time I was in a T engine
Well I just have another shot of jamison's and just in tall my next part
No worries but getting cold to cold for beer so jamison and coffee mostly now
You can NOT put the cam gear on the camshaft a half turn off (180 degrees). There are no pin holes to line it up wrong. If you put the cam so the valves of #1 or #4 are rocking, the pistons of that cylinder will be down and the cam is 180 degrees off. It won't run that way.
The pistons of one and four gotta be up when the valves are rocking and the timing marks line up.
The T is no different than any other 4 cycle engine.
When you turn the crankshaft a complete turn the marks no longer line up. That's because number 4 is in firing position and the cam only went around a half turn, just like when you turn your model A or Toyota or Chevy a complete 360 degree turn of the crank which only turns the cam 180.
If you turn the cam 180 degrees you're still ok.
If you turn the crank 180 degrees without turning the cam you're dead in the water, that's why they have timing marks.
No mystery at all.
Charley, don't try to figure it out.
I have seen a couple of real good mechanics that could not get it straight in their minds.
They could not pull a gear driven distributor and get it back in to fire up to save their lives.
I can't figure out radios and TVs. I can't post a picture on this site, but I can figure out cam & distributor timing. No big deal.
The thing is, you, Charley can put a T together and make it run. Don't tell anybody you can't figure out why it will run. I damn sure won't tell on you.
Forget moderns. They have (usually) key ways on both shafts so the gears can only be installed one way. The T has 2 pins on the cam shaft flange for mounting the gear and the gear can be mounted in 2 positions. The T IS different from a modern because of this difference. You CAN mount the gear either way. Again, if you have a Mac's catalog (only because of the clear pictures) you'll easily see this. You CAN mount the gear 2 ways on the shaft and the engine WILL run. It's been proven because it's been done. I'll say it for the umpteenet time: In one position #1 cyl (for example) at TDC will be on compression. At the other position #1 cyl at TDC will be at the end of the exhaust stroke. All other cyls. follow suit and the roller is correct also.
I believe, in fact I'm sure, I've figured it out why it works in both positions. Here's another shot: I'll again use #1 piston at TDC (as an example). Put the gear on the cam one way and both valves are closed on #1. That's compression where the plug fires. Put the gear on the cam in 180 out and the exhaust valve for #1 is open. That's the end of the exhaust stroke. Crank the engine and you'll find that everything operates normally for all cylinders and the timer roller is correct. The roller is in another position but it's still correct for firing the cyls.
You make it sound complicated Charlie, leave the crank alone, #1 and #4 piston are ATDC, roller is firing #1 in relation to the lobes being on the heel,closed valves, #4 valves are rocking, rotate cam 180degrees now roller is firing #4 and lobes are on the heel,closed valves, #1 valves are rocking.
I think I said that using only one cylinder.
If you think getting this in your head is complicated, try the phantom spark theory. This is when #1 and #4 fire at the same time and #2 and #3 fire at the same time. This kind of ignition is common in many modern engines and even some Model T timers used this technology.
It is my understanding that the True Fire does that.
What you wanna bet that the reason that when the timing marks are lined up, #1 is NOT at TDC was to avoid this very confusion? The timing marks are there to time the camshaft to the crankshaft. PERIOD. Not to put #1 piston in firing position. If it did, and you put the gear on in the other position, #4 would be in firing position and everyone would be confused. So they made it where NO piston is in firing position with the marks lined up. Just a theory.
Just using TDC as an example to explain. I understand its not the case with the T but can't think of a reason why it should or should not be.
Simple, cam does not care, marks lined up it will either fire on no.1 or no. 4 makes no difference except early cam with hole drilled through then roller can be turned 180 out even at that you could change wire position on the timer and would run. Does this add to the confusion? KGB
Actually it's been said a few times before and to answer your question......YES!! LOL.
The Model T firing order is 1,2,4,3. The cam is turning at 1/2 crank speed. Remember that when #1 is at top dead center #4 is also at top dead center. If you have it at top dead center compression stroke of cylinder 1 then #4 is at top dead center on its exhaust stroke. So if you have the motor set up with #1 at top dead center on compression and then turned the cam 180 degrees then cylinder 4 would be on compression and #1 would be on exhaust.
Yes, but it makes no difference.
I think that's what Paul is trying to say.
Oh, I misunderstood. Sorry.