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Rebuilding the race motor.
https://slantsix.org/forum/viewtopic.php?t=56886		 Page 2 of 3
Author:  SpaceFrank [ Thu Jan 29, 2015 7:06 pm ]
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Just to be sure, how bad is too bad for a cylinder ridge? These ridges aren't bad enough to "catch a fingernail on," but they are enough to feel with your finger. The telescoping bore gauge isn't exactly the most precise instrument in the world (in my hands), but as near as I can tell, the ridges are no more than 0.001" thick per side (0.002" on the diameter). Probably less.

In fact, the more I use this bore gauge, the better I feel about the condition of the bore. The observed range in the diametrical measurements I took the other day was 0.004". This is within the allowable tolerance listed in the FSM (0.005" for out-of-round and 0.010" for taper), but I'm guessing most of that is actually scatter due to sausage fingers. The actual variation is probably much less than that.
Author:  sandy in BC [ Thu Jan 29, 2015 7:18 pm ]
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If the ridge is small enough it will disappear when you hone,

,,otherwise you need to use a ridge reamer (can really make a mess in the wrong hands),,,,,,,,

As stated earlier I prefer to hand file the ridge out, ...this puts a slight taper at the top of the bore....stay inside the gasket fire ring.
Author:  Dart270 [ Fri Jan 30, 2015 6:52 am ]
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For that size ridge, and assuming you cleanly got the old pistons out (w/o beating on them), personally I would just hone it and not try to clean up the ridge in any way. YMMV...

Lou
Author:  SpaceFrank [ Fri Jan 30, 2015 8:27 am ]
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Okay, one final question before we get down to it. I totally neglected to pay attention to the grit numbers, and I now own a 120-grit flex-hone. A little more research is leading me to believe this is too coarse. Supposedly, for stock iron rings you should use a hone in the 180-240 range? Will I screw things up if I use this 120-grit hone?

FYI, the rings and bearings I bought are all Sealed Power.
Author:  CNC-Dude [ Fri Jan 30, 2015 10:24 am ]
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Yes, your hone is much too coarse. Stock cast rings usually get finish honed with a 525 grit stone. Moly rings need 625 grit or finer.
Author:  Dart270 [ Fri Jan 30, 2015 10:29 am ]
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I'll have to check, but I think I did my last re-hone on previously used cast pistons and cast rings w/a 200-240 grit dingle ball hone. 120 sounds too coarse for sure. That would be for cleaning up bores with lots of grooves/scratches, then followed by finer stones.

For fresh overbore and pistons, I agree that a significantly finer stone should be used.

Lou
Author:  sandy in BC [ Fri Jan 30, 2015 11:52 am ]
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Hang ontothre coarse stones....someday you will need to clean up a rusty bore.

I use 240 grit parallel stones on a variable speed drill. I keep an pld block on hand to "Try " things on . I give that block a lil "test hone" to get the rythym and speed right.

All you want to do here is get rid of the ridge so you wont bust the new rings,,,,and to cut into the "glazed " bore enough to make some teeth to abrade you new rings.

If the original hatching is still visible a quick whisk with a fine stone will do it.

If the motor has been real hot....and the bores look like mirrors you may need to get more aggressive.

I suggest honing the shyte out of some junk block to see what happens first. " Hold my beer...I want to try something...."
Author:  SpaceFrank [ Mon Feb 02, 2015 8:39 pm ]
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One more complication discovered while cleaning pistons. On at least one of the pistons, it looks like the top ring groove has been distorted. The ring groove itself is definitely wider on one side, as if the ring wallowed it out or pressed upward enough to bend the lip of the ring land outward. Not the best pictures ever, but this should be enough to show the damage. You can definitely see how the piston itself has rubbed on the cylinder wall just above the ring groove.

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The obvious question is whether this piston should be re-used. Is there a specification for the width of the groove, or something else I should check? If only one or two pistons are bad, can I get away with just replacing the bad ones, or should I swap out all 6?

The piston in the pictures (#3) is also one of those that has a little resistance in the wrist pin rotation. What are the chances that the wrist pin or connecting rod itself is bad, and where can I find these? Con rods don't seem to be as readily available as replacement pistons.
Author:  CNC-Dude [ Mon Feb 02, 2015 11:37 pm ]
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You probably are seeing evidence of lifting the ring lands. Stick some feeler gauges around the periphery to determine how bad the worst spots are. Anything more than about .003"-.005" clearance with a new ring should be replaced.
Author:  Charrlie_S [ Tue Feb 03, 2015 4:20 am ]
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Quote:
What are the chances that the wrist pin or connecting rod itself is bad, and where can I find these? Con rods don't seem to be as readily available as replacement pistons.
198 rods are very hard to find. 170 rods are also hard to find, but not as bad.
225 rods are readily available, both as new and reconditioned. If you need some, I have NOS 225 rods in stock. Send me a PM.
Author:  Dart270 [ Tue Feb 03, 2015 5:12 am ]
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I would definitely not use that piston. Overheating the piston, almost certainly. This is probably why some of the pistons are stiff rotating on the rod pins too? Several of us have boxes full of old 225 rods.

Lou
Author:  SpaceFrank [ Tue Feb 03, 2015 9:11 am ]
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Okay, if we're going to be replacing pistons and rods, I would like to look into getting something better than stock replacement. Even if we manage to keep it cooler than before, this engine will continue to get beat on. We'll probably end up turbocharging it later as well. Any recommendations for forged or otherwise stouter internals? Is anything available along these lines?

FYI, the pistons I just pulled out are Sealed Power 244NP +.030" cast pistons. They were new when the engine was rebuilt in 2004. I'm not sure if the rods were also replaced at that time.
Author:  CNC-Dude [ Tue Feb 03, 2015 10:01 am ]
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Most any forged piston you need to use is available from any of the dozens of performance piston companies that make pistons. They are not likely to be "on the shelf" though, but are available custom with just a phone call. And since you stated in the title its a race engine, I wouldn't expect to use anything less than a forged quality piston.
Author:  SpaceFrank [ Fri Feb 06, 2015 2:04 pm ]
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All the other pistons appear to have acceptable ring groove clearance and no obvious damage like the one in the pictures, so I just ordered one replacement. Delivery is setting our schedule back some, so we won't be assembling the short block until next week. We completed the hone job, though, and the cross-hatch looks pretty good. Now we're prepping everything we can and continuing work on the transmission rebuild until UPS comes.

Just want to be exactly sure on ring gap. I'd been reading that 0.010-0.020" was a pretty typical stock range, but my FSM actually gives 0.010-0.045" as the acceptable specification. Lou recommended "high side of stock" for endurance racing, but I'm not sure which range he was referring to; that could mean 0.020ish or 0.040ish. The new rings come out of the box around 0.015". We also measured the existing gap on the surviving used rings (just the second rings- the only surviving top ring broke in disassembly), and they were in the range of 0.028-0.035. Would they have opened up significantly due to wear in service?

Anyway, I definitely intend to set them loose, I'm just not sure how loose. I've got no qualms about a little blow-by, but I don't want to go overboard for no reason.
Author:  SpaceFrank [ Sat Feb 07, 2015 10:40 pm ]
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Good news: the new piston somehow magically showed up today.

Bad news: although the Sealed Power part number is the same, this is quite obviously a different casting with a slightly longer skirt and what appears to be some heavier reinforcement inside. The new piston weighs about 1.5 oz. (40ish grams) more than the old ones. As far as I can tell, this is way too much difference, and there's no way I feel comfortable performing the kind of major surgery that would be necessary to remove 40 g from a piston.

So it looks like we're ordering a full set of six now, unless anyone can tell me how to find an exact replacement for the smaller old one pictured on the left (0.030" over).

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