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One thing I noticed while trying measure cam lobe to lifter clearances on a 98 Mazda 626 GF 2L, was that when I rotate the crankshaft there seems to be one spot where I have to put in a lot more effort to turn it than in the rest of the revolution. Like it was really sticking at one particular spot.

Is that indicative of anything?

EDIT

It felt a little stiff when valves I1+E3 were about to open, when I4+E2 were about to open and really stiff when I3+E4 were about to open.

If I got a good momentum going while turning the crankshaft I didn't feel it so much.

Also measured cam to lifter clearances. Spec is 0.23mm to 0.30mm

+---------+-----+-----+-----+-----+
| Cyl #   |  1  |  2  |  3  |  4  |
+---------+-----+-----+-----+-----+
| Intake  | .24 | .29 | .24 | .24 |
+---------+-----+-----+-----+-----+
| Exhaust | .29 | .24 | .29 | .24 |
+---------+-----+-----+-----+-----+

Not sure what to make of it, maybe some of the spring are just a little stiffer than others?

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  • 1
    Is that every revolution in the same place, or every other revolution? Roughly how many degrees of the 360 is it tight for?
    – HandyHowie
    Commented Nov 16, 2015 at 20:48
  • 2
    Did you remove the sparkplugs prior to rotating the engine?
    – DucatiKiller
    Commented Nov 16, 2015 at 23:23
  • 2
    @DucatKiller Yes, I'm not a complete dufus :-)
    – Robert S. Barnes
    Commented Nov 17, 2015 at 4:38
  • Have you checked your timing? Whenever I run into an issue similar to what you describe, it tends to be a jumped belt, or chain tooth.
    – cloudnyn3
    Commented Nov 18, 2015 at 20:44
  • @cloudnyn3 First thing I checked, all timing marks line up like they should.
    – Robert S. Barnes
    Commented Nov 19, 2015 at 5:37

1 Answer 1

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When rotating a 2 or 4 stroke motor there is an illusion of sticking between TDC and BDC. The rings are reaching their maximum friction coefficient at that time do to maximum distance traveled within the bore.

So, it may seem as thought there is a sticking issue, in actuality it is an innate feature of a two or four stroke ICE.

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1
  • 1
    So what I should really worry about is the ones that don't feel like they're sticking?
    – Robert S. Barnes
    Commented Dec 19, 2015 at 18:38

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