Does my engine spin too easily?

[MotoMike]

I finally got all my parts assembled to check the timing in my 450 yesterday. While determining TDC, I found that with no plug in the head, the engine spins very easily. In fact, it has a tendency to fall off a few degrees one side of the other after being positioned right at TDC. I don't think I've had a roller bearing motor before and know they can spin easy, but thought the rings should hold it tight in the cylinder. It seems to have good compression, when rotating it around in preparation for starting; I come up against a wall on the compression stroke and have to ease it over the top to kick it over. It is now typically starting on the first kick and seems to run very well. I really haven't put a lot of miles on it in the last couple years, but I am not seeing oil consumption. The clock shows 11kmiles but I have no way of knowing if that is correct or not.

Your thoughts are appreciated.

Mike

[Bevel bob]

Sounds like a good-un. My motor was not free , it had a missaligned crank. Its free now and goes like the clappers.

[kmev]

I just timed my newly-rebuilt 250 and had the same problem with rolling past TDC in either direction. It was impossible to stop directly on TDC. I ended up "bumping" the engine slowly forward in small increments by turing the rear wheel while in 5th gear. Probably not good for the bearings or gears, but I did manage to find exactly where the points were opening.

[MotoMike]

thanks gents
Mike

[LaceyDucati]

Hi Mike

Could just be the magnets of the alternator pulling the crank around a bit. Can be a pain on a road engine when setting up some systems, I always notice it as I work on a lot of race engines with no alternators. All else sounds fine, so probably nothing to worry about. A nice free engine is a good thing & the standard borgo rings are fairly free when bedded in, no expander behind the oil ring.

Nigel

[MotoMike]

Thanks Nigel
that makes sense and was an "aha" moment for me as it did not occur to me before.
much appreciated.
Mike

[3564cam]

I had exaclty the same on my 125 after I fitted the new 12 coil Electrix alternator.It would stick in certain places.I was worried something was binding but then counted the "tight" spots and it had 12,the same number as the number of coils !
Steve

[DewCatTea-Bob]

____ Of course the rotor-poles would naturally always tend to pull themselves towards the stator-poles, (providing there's no encountered resistance to prevent so), and I'd expect that rotational-draw to occur until the center-points of all the poles have exactly/ideally aligned (center-points to center-points).
And it's at that particular rotor & stator alignment-point when the alternator happens to produce it's 'peak' power. _ Therefore that point ought to be made to occur just-prior to when the static-ign.spark is expected to occur, (for best spark-production at kick-over speeds) !
__ So for Steve's 125, even with a 12-pole alignment, it helps to 'time' the rotor,, and so with the 125, one of those noted 12 alignment-points ought to be set/timed to occur about 20-degrees before TopDeadCenter next occurs.
But what doesn't make expected logical-sense is that MotoMike's 450 (which is supposed to have a 0-degree/TDC static spark-timing), isn't fully content to stay-put exactly aligned right at TDC. ...
Now I can understand reason for having the peak-power occur a couple degrees sooner, (so as to be sure of full-saturation of the ign.coil, when most needed), but otherwise, it seems to me (from what Mike has posted), that HIS 450 is likely not timed for highest power-output at TDC (when the 450's ign.spark could best make good-use of it).
And while Mike's post didn't make note of the exact rotation amounts which the crank pulled-away from TDC, if his crank pulls-away near equal-distant ether way from TDC, then it's certain that his alt.rotor is well off-time, (from a most logical standpoint).
____ Is there anyone not clear on what I'm meaning to make note of here ?


Questionable-Cheers,
-Bob

[MotoMike]

____ But what doesn't make expected logical-sense is that MotoMike's 450 (which is supposed to have a 0-degree/TDC static spark-timing), isn't fully content to stay-put exactly aligned right at TDC. ...
Now I can understand reason for having the peak-power occur a couple degrees sooner, (so as to be sure of full-saturation of the ign.coil, when most needed), but otherwise, it seems to me (from what Mike has posted), that HIS 450 is likely not timed for highest power-output at TDC (when the 450's ign.spark could best make good-use of it).
And while Mike's post didn't make note of the exact rotation amounts which the crank pulled-away from TDC, if his crank pulls-away near equal-distant ether way from TDC, then it's certain that his alt.rotor is well off-time, (from a most logical standpoint).
____ Is there anyone not clear on what I'm meaning to make note of here ?


Questionable-Cheers,
-Bob

Thanks Bob, you are correct. I have long known that the rotor was not properly timed. I always suspected that the shop where I got it (pretty strictly a brit bike shop at the time) just made sure it ran and didn't focus on the fine points. There used to be a master battery switch and if you turned it off the bike immediately died. I have just never gotten around to correcting the flaw. Had resigned myself to study the issue more before attempting it. Can't remember just what the issue was but thought I remembered there was some disagreement about how to get it just right. Plus I have not fashioned or acquired a puller to get the flywheel/rotor off.

[DewCatTea-Bob]

" I have long known that the rotor was not properly timed.
There used to be a master battery switch and if you turned it off the bike immediately died. "

____ Such die-off may still occur even with the alt.rotor properly timed, when engine-revs are too low,, but above idle, the alt.power alone should maintain runnable ign.spark without any help from a battery,, (although the w-c rect.reg-box will suffer possible burn-out if ran for long without battery connected - [so any concocted battery master-switch is not a good idea then!] ).


" Can't remember just what the issue was but thought I remembered there was some disagreement about how to get it just right. "

____ I don't recall of any such contested issue concerning the alt.rotor's exact 'timing', except for that I-myself have discovered that the 'timing-mark' factory-placed on many rotors are inconsistently located (in relation to the magnet-arrangement), and thus the provided setting-charts are not to be solely trusted.
__ Or perhaps the issue was actually about the 450's recommended static-timing setting, which ought to be 3 or 4 degrees BTDC (for best performance), rather than the (anti-kickback) factory-setting of zer0-degrees.
In which case the alt.rotor then ought to be set to produce peak-power at about 5-degrees before TDC.


" Plus I have not fashioned or acquired a puller to get the flywheel/rotor off. "

____ There's a couple eBay-sellers who have them listed for around 50-bucks,, and after you're done with one, you could no-doubt sell it off (to somebody here) for over 50% of it's cost.


Hopeful-Cheers,
-Bob