360 build.

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trigger_andy said:
Not scoring the crowns? It that an issue? What could happen? Create a weak spot maybe? Or somewhere where heat can build up?
Click to expand...
All of the above, plus stress riser/crack fissures. Especially with garden grade cast pistons.
 
Best wishes and best of luck with the build, though, hoping it goes well!
 
Yes. A hot spot(s). You don’t want to gouge the piston. Brush marks are fine. That’s why the suggestion of a brass brush comes in. A soft steel brush is ok.
 
Slightly off topic but to save starting another thread I thought maybe you knowledgeable guys might offer some light.

The 340 thats burning smoke had new Valve Stem Oil Seals installed by myself, but in my infinite wisdom I never checked for valve play. Im burning Oil on Cylinders #1 and #7. Im getting 115psi on all cylinders on that bank and Im getting 40 psi oil pressure from cold and about 25psi at 1500rpm driving when warm. But Im getting a good amount of blue smoke when idling and under acceleration and more so with hard acceleration.


Could this be the Valves/Valve Stem seals or most likely the Rings? If there's a chance its the Heads I'd whip them off and put on a set of freshly built heads with the 2.02" Valves.

There is a definite ridge at the top of the cylinders, I remember that from when I had had the heads off before. (due to a burned out valve. But that was on all the cylinders and only 2 seem to be burning oil.

Cheers,

Andy
 
Jadaharabi said:
Sounds like loose pistons to me. Just a guess since I'm not standing beside it.
Click to expand...

Lose pistons? Ie needing bored? That was the plan when I swap it out for the 360 but when Im getting the same 115psi compression it seems a little odd. But I have limited experience so I really dont know. :D
 
if it's not the stem seal then it's the rings
new seals should even seal bad guides- for a while
do a leak down test
I can't remember the thread but if this is just a temporary motor till you build a 360 you can take it apart and clean gently remove the ridge, hone, knurl the pistons and slap on a set of cheap rings -depending on what you find when you mic the bores
if those are KB pistons remember to set the ring gaps for those pistons
you could also move the rotating assembly to a different block and save the cost of pistons
but you would have to bore the new block for these pistons
that compression is way off for those pistons and it will never run right with that much oil
was this balanced or do you know
if the plugs are fouling and you have to limp it along for awhile try Champion RFN14LYC or
Champion 82 Spark Plug RFN14LY
 
Wyrmrider said:
if it's not the stem seal then it's the rings
new seals should even seal bad guides- for a while
do a leak down test
I can't remember the thread but if this is just a temporary motor till you build a 360 you can take it apart and clean gently remove the ridge, hone, knurl the pistons and slap on a set of cheap rings -depending on what you find when you mic the bores
if those are KB pistons remember to set the ring gaps for those pistons
you could also move the rotating assembly to a different block and save the cost of pistons
but you would have to bore the new block for these pistons
that compression is way off for those pistons and it will never run right with that much oil
was this balanced or do you know
if the plugs are fouling and you have to limp it along for awhile try Champion RFN14LYC or
Champion 82 Spark Plug RFN14LY
Click to expand...

I think the seals did hold for a short while. But not for long, ie a matter of days before I noticed the smoke was back. But Im not 100% of this, which is frustrating to say the least.

I'd have to look into how to perform a leak down test, cheers. :)

The 340 still screams. It rips right up to 5000rpm and the porting I did on the 587 1.88" Valve heads and the .060" Mill seems to have made a noticeable difference. The main reason for pulling it is the blue smoke and fouling issue. If I could simply change the Heads and stop this issue the 360 could go on the back burner and get some nicer bits. :)

The 340 is stock, not KB Pistons. Just crappy 1973 Cast ones. :D

I'll try those plugs for sure. :) Cheers.
 
I've tried those plugs on 318 and 360 but not 340 make sure they clear the pistons (they were a plug developed for AMC 6, really smooths out the idle)
there are many versions both 13/16 and 5/8 hex
should work as you do not seem to have the high compression 340

"if they close up the gaps" when you turn it over use standard projected core plugs- use a breaker bar screw the plug in a couple of threads then roll the motor over
tighten the plug a little, repeat if they clear tight open the gap and try it- then run it this plug type works wonders on any low compression motor where it fits
I was with AMC when we made the switch from rn12yc style made a big difference, we started retrofitting with feedback then AMC put out a service bulletin (PS real reason it cuts misfires and therefore smog)
thanks for the heads up on the pistons- hard to tell from the pic and someone thought they were kbs
you may be able to get a leak down tester at an auto parts store rental you will need a compressor
did you try squirting some oil in the cylinders on the low side and repeat the compression test? with the throttle open and ignition dead don't want no fires
 
Wyrmrider said:
I've tried those plugs on 318 and 360 but not 340 make sure they clear the pistons (they were a plug developed for AMC 6, really smooths out the idle)
there are many versions both 13/16 and 5/8 hex
should work as you do not seem to have the high compression 340

"if they close up the gaps" when you turn it over use standard projected core plugs- use a breaker bar screw the plug in a couple of threads then roll the motor over
tighten the plug a little, repeat if they clear tight open the gap and try it- then run it this plug type works wonders on any low compression motor where it fits
I was with AMC when we made the switch from rn12yc style made a big difference, we started retrofitting with feedback then AMC put out a service bulletin (PS real reason it cuts misfires and therefore smog)
thanks for the heads up on the pistons- hard to tell from the pic and someone thought they were kbs
you may be able to get a leak down tester at an auto parts store rental you will need a compressor
did you try squirting some oil in the cylinders on the low side and repeat the compression test? with the throttle open and ignition dead don't want no fires
Click to expand...


Well these plugs arrived today. What a difference off the idle. Thank you very much for the heads-up on them.

I have a miss-fire between idle and 3000rpm. At least thats where its noticeable. The engine really picks up after this. I'll start looking at what I need to do to rectify this but any heads-up will be gratefully received.
 
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