318 piston ring gap

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gliderider06

gliderider06

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So, I have a 88 roller 318 I'm thinking about freshening up for my 87 Ramcharger. It will be stock except for a spreadbore Intake. The motor has beautiful cylinders. No ridge and still has some cross hatches visible. Now, before I start popping pistons out, I look in the engine bible and they say the gaps should be .012/.014" top, .006/.009 second. My FSM, says .010-.020" both rings. I have a new set of Hastings rings and the box says .004 per 1" bore which = .016".
Which do I go by? The FSM for 1987, the rings or the DC bible?
 
Use the hastings recommendation, they made the rings and it is in the middle of FSM tolerances.
 
sireland67 said:
Use the hastings recommendation, they made the rings and it is in the middle of FSM tolerances.
Click to expand...
Thanks, I kinda was thinking that too. I'm curious to see what the ring gap is on the factory pistons.
 
depends on the piston
how far down from the tops are the rings
and what piston materiel?
hyperutectics take much more gap
no way the ring mfg can know this
would work on rebuilder cast pistons
that's about it
 
I've been running around .014-.016" for decades with all sorts of engine in this range with stock ring heights and 3.6-4" bores with no blowby or other issues. The 340's KB hypers got a lot larger top ring gap, as did some Arias forged pistons in my new Opel engine, both of which have the top rings way up on the pistons.

BTW, OP, check ring side clearance before you try to re-use the original pistons. That has a BIG effect on the ring seal and blowby. Re-using pistons with worn ring grooves are a waste of time, and replacement stockers are cheap.
 
Ok, I took a piston out today. Factory rings have about .025" ring gap maybe a tad more. Side clearance calls for .0015-.004" My smallest feeler gauge is .006 and nowhere close to being able to squeeze it in there. My new rings have about .017" end gap, so with a quick deglazing I will be fine. The bearings still look brand new and the crosshatches are very noticeable.
Since the lifter valley has gotten dirty from sitting w/o an intake, I'm going to tear it down and run it to the machine shop to have them give it a bath and ball hone it for me. Piston skirts look great too with minimal marks.
15857822181901168217210927983012.jpg


15857822930437799179837187908827.jpg
 
And.. Harbor Freight has feeler gauge sets that go down to .002" for very little $$. Check all you piston side clearances.... the wear can and does vary.

Sounds pretty solid so far. Make sure they don't over do it with the fresh hone and open things up a lot. Interesting machining on the tops and side of the lifter bores. I've never seen one of those block.
 
Two questions, since I'm about to start (re)assembling my 318 LA. Which engine bible are you referring to?

And how do you accurately measure the ring gap? The block has been bored to 0.030 over, so I've got no ridge at the top. Load the piston into the cylinder, and bring it up just high enough where the ring is almost at the top of the bore and measure then?
 
Stick the ring in the bore and level it with the piston top then measure the gap. That works with flat tops. I like to measure down a inch or so. It get's past any taper.
 
toolmanmike said:
Stick the ring in the bore and level it with the piston top then measure the gap. That works with flat tops. I like to measure down a inch or so. It get's past any taper.
Click to expand...
Yep, just flip a piston over with no rings on it, and use it push the ring down about 1/2-1" from the top (or where you think is most critical), pull out the piston, and measure. If tapered, I would want know the situation at the top and down in the bore too.
 
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