• From: Pilot Hill Ca.
  • Registered: 2006-12-04
  • Posts: 69

Topic: If you have done many rebuilds you might be able to answer this

Ok I have this 1600 i picked up.It runs but has a bad knock so i took it a part today to check the pistons.all the pistons i have seen have a arrow to point them at the flywheel.No arrow on the top. has STD stamped on them and a little notch on the the edge.So which way do they go in?The pistons seem new and the heads too.The person who rebuilt it stopped because of the knock.no.1,3 and 4 the notch are one way and no. 2 the notch is another way.can anyone help
thanks James

Pilot Hill Ca.
  • From: City of Roses
  • Registered: 2004-03-29
  • Posts: 793

Re: If you have done many rebuilds you might be able to answer this

Hiya Gold,

The arrow on the piston top should point toward the flywheel.

Have you checked the connecting rods for their "bump" orientation?  If the connecting rods are installed correctly each will have a bump pointing up on the rod between the small and large ends.

Mike

1970 AS Bug
1970 Bus - The Ruptured Duck
  • From: Pilot Hill Ca.
  • Registered: 2006-12-04
  • Posts: 69

Re: If you have done many rebuilds you might be able to answer this

thanks books I will check that to.I have no arrows that is the question

Pilot Hill Ca.
  • Registered: 2010-04-15
  • Posts: 15

Re: If you have done many rebuilds you might be able to answer this

I had a set once that the notch was the arrow, # 2 being the other way from 1,3,4 may be the problem. the cast bumps on the rod sides must be up when your looking down at your case, as it sits level on your stand. rods and pistons both are off set. And next. lift your cam out and look at the bearings. if your case has been line bored and you got yourself the wrong main bearings it will show up on the cams in short order. you still need to get in there with an inside mic and dbl check. But the tell tale sign that the main b's are either wrong or were not set in the indexing pins fully when the crank was set will show up in the cam b's looking like hell even before you get in there with a mic. Just my 2 cents worth. there is not to much that can be screwed up that i have not fubared myself including that knock your hearing I'm guessing at around 1000 rpm, sounds like hell as you thot up to about 2500 and you can almost get rid of by retarding the timing.  Almost.

  • From: Ontario, Canada
  • Registered: 2005-06-11
  • Posts: 266

Re: If you have done many rebuilds you might be able to answer this

If the crank rotates clockwise and the pistons are at dead center, then the wrist pins must be offset high on the 1/2 side and low on the 3/4 side so that at TDC the piston doesn't ram into the crank at a straight angle.  (At least this is what logic tells me, but I'm sure theres a manual out there to verify this...? anyone?)

If you've got the pistons out, you might as well measure them to confirm if the wrist pin is high or low and verify that the notch points to the flywheel (which it likely does.)

Any idea how long it was run with this "knock?"   If it was any length of time, you might have started to destroy your main bearings even if they were brand new, since an inverted piston would be smashing the crank at a straight angle (or an acute angle, which is even worse.)    .. but this is just me being a worst-case-scenario type of guy wink

Ditto on the checking the connecting rod bumps. If you're splitting the case, make sure that the connecting rod "bottom" lines up with the "top" piece so that the stamped numbers are both meeting on the same side.

-biggie

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