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Old 08-29-2007, 05:00 PM
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Need help,Pontiac 400

I posted this over on a pontiac site and had a few good replies but I had allready tried that did not help.Such as the pvc valve, modulator valve,and the full throttle runs from a 30 mph kick.
How is it going guys? This is my first post, I have really enjoyd searchin and reading this site.Awsome site!
I have a 70 GTO that i have finished a frame off on.It has a # matching YS 350 HP 400, with #13 heads.It has been bored .30 over and has speedpro forged pistons and molly rings and Comp cams K kit,with the XE 268,995 springs,locks,
an retainers.The heads:Valve job, guids K liners,Intakes were cut for the positive seals,the exhaust with original o-rings only.
As far as the performance goes the motor runs and sounds great.The problem i am having is Smoke. I had 800 miles on the rebuild and was still smokeing I tore it down rehoned with 400 grit 3 finger hone,installed seald power molly rings,piston to wall clearance was .004(Rings were installed corect,and end gap of .020 ).At this point it has 600 miles and still smokes. Mostly at first startup( small cloud then clears to less at idle)You can see lihgt smoke wile driving at times.
I have 15 " of vacum and no vacume leaks,and when i tore it down the intake runners (Original intake,heads,intake had not been machined)had heavy oil buildup and on the piston tops.With that much oil why do my plugs show no signs of oil? they are white - tannish.
I did do a compression test.

Dry Wet

1 175 1 180
3 170 3 180
5 170 5 180
7 168 7 180

2 170 2 180
4 168 4 185
6 175 6 185
8 175 8 180

Some people tell me to drive it that it is the rings and they will seat , what do you guys think?Sorry for so long of a post.Any replies or advise I would really be thankfull for.

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  #2 (permalink)  
Old 08-29-2007, 05:46 PM
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Quote:
Originally Posted by BEN24
I posted this over on a pontiac site and had a few good replies but I had allready tried that did not help.Such as the pvc valve, modulator valve,and the full throttle runs from a 30 mph kick.
How is it going guys? This is my first post, I have really enjoyd searchin and reading this site.Awsome site!
I have a 70 GTO that i have finished a frame off on.It has a # matching YS 350 HP 400, with #13 heads.It has been bored .30 over and has speedpro forged pistons and molly rings and Comp cams K kit,with the XE 268,995 springs,locks,
an retainers.The heads:Valve job, guids K liners,Intakes were cut for the positive seals,the exhaust with original o-rings only.
As far as the performance goes the motor runs and sounds great.The problem i am having is Smoke. I had 800 miles on the rebuild and was still smokeing I tore it down rehoned with 400 grit 3 finger hone,installed seald power molly rings,piston to wall clearance was .004(Rings were installed corect,and end gap of .020 ).At this point it has 600 miles and still smokes. Mostly at first startup( small cloud then clears to less at idle)You can see lihgt smoke wile driving at times.
I have 15 " of vacum and no vacume leaks,and when i tore it down the intake runners (Original intake,heads,intake had not been machined)had heavy oil buildup and on the piston tops.With that much oil why do my plugs show no signs of oil? they are white - tannish.
I did do a compression test.

Dry Wet

1 175 1 180
3 170 3 180
5 170 5 180
7 168 7 180

2 170 2 180
4 168 4 185
6 175 6 185
8 175 8 180

Some people tell me to drive it that it is the rings and they will seat , what do you guys think?Sorry for so long of a post.Any replies or advise I would really be thankfull for.
A moly ring should have a pretty smooth wall, like that obtained with a 600 stone. Never use those abrasive brushes. Forged pistons are a PIA in a street motor, they always require extra clearance because of their substantial expansion/contraction rate with temperature. This requires that the engine be carefully warmed up before getting on the gas so that the piston can stabilize its temp and establish proper operating clearance. When the engine is cold, the piston slaps back and forth between it thrust and counter thrust faces, this movement in its extreme can crack a piston skirt, even bust a cylinder wall, one of its more minor difficulties is that the rocking breaks the ring seal on the wall allowing compression to leak past the piston and causing the oil and second ring to allow oil to stay behind on the cylinder walls. resulting in smoking.

The problem with rehoning is the clearance keeps getting bigger and oil control problems with it.

The heads, so they were done, but with-in spec? It only takes one loose guide to pull enough oil to make a hazy exhaust.

The smoke, is it all the time, on acceleration, with a dropped throttle (coasting)? All the time is a good indicator that the rings aren't getting a hold of the wall, could be a broken ring, too much end gap, back to piston slap causing the ring to kock (trying to outsmart the dirty word checker with miss-spelling) against the wall and not wiping oil off, a broken piston skirt, a broken cylinder wall, too much side clearance between the skirt and wall. Upon acceleration is the some of the same issues where the rings are either not wiping the wall properly, excess combustion pressure is entering the crankcase which will exacerbate this problem by applying pressure in the case which then forces oil past the rings of cylinders that are on the intake stroke. On a dropped throttle the problem is high vacuum in the intake is drawing oil past the guides, or once again the rings aren't riding the cylinder walls properly and the top end vacuum is pulling oil around the piston.

A compression test is some good data but a leakdown test is better at getting to whether you're getting proper ring seal. Although leakage past the rings with the engine at rest maybe considerably less than when it's running. but still it's better info.

Lets not forget crud building up on the ring lands preventing the ring from making a seal on the piston side. People tend to worry the ring to cylinder wall to death when it comes to sealing, but. OK a big BUT, the top and bottom of the piston's ring lands are a sealing surface, so is the top and bottom surface of the ring. Any gunk on those surfaces allows the leakage of compression out and oil into the upper cylinder. Oil getting in there and coking (forming hard carbon) will break the seal. Also, the ring groove must be deep enough to allow the ring to never bottom in the groove. Normal ring tension against the cylinder wall is insufficient to make a seal, the seal, especially that of the top ring is 100% dependent upon compression and power stroke pressure that leaks around the crown of the piston to leak behind the ring which forces it into the wall with some authority. The second ring is really more of a pressure catch all and while dependent upon some leakage past the upper to make a seal, its real job is oil control. These have an up and bottom side, if installed backwards or upside down, they will not wipe oil from the wall, in fact they will actually pump oil into the upper ring's gap and into the combustion chamber.

So oil leakage is a self-destructive feedback mechanism that goes from bad to worse because the carbon products left behind when it burns or cokes in the ring lands keeps the rings from sealing which pumps more oil which makes more coking products which lets even more oil through. And so it goes.

Plus a 400 has pretty thin walls, thirty over may be more than some blocks are happy with. If the walls are flexing, kiss ring seal good-bye

Bogie
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Old 08-29-2007, 08:05 PM
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pontiac 400

hi, is your 3 finger hone actually a deglazer? sam-missle
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Old 09-05-2007, 01:09 PM
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I found out the retainers could be pounding the pc seals .I didnt wont to take the heads off to have the guids machined again.the machine shop had machined them for pc seals but did not machine them down as far as the height so that it could handle the 480 lift,the retainers were pounding the seals and letting oil pass the seals and guids, causing all the smoke .I had a stock cam 407 lift i swaped cams and that did the trick.Thanks for the replies
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Old 09-05-2007, 01:26 PM
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Quote:
Originally Posted by BEN24
I found out the retainers could be pounding the pc seals .I didnt wont to take the heads off to have the guids machined again.the machine shop had machined them for pc seals but did not machine them down as far as the height so that it could handle the 480 lift,the retainers were pounding the seals and letting oil pass the seals and guids, causing all the smoke .I had a stock cam 407 lift i swaped cams and that did the trick.Thanks for the replies
Yeah, there is a little trick here being that the upper guide boss not only requires machining for a positive stem seal, but before that happens it needs to be machined for several other things:

- If you're using a spring not native to that head, the upper guide and outer spring pocket may need to be machined for outer and inner diameter clearance of the spring.

- If you're changing the cam or rocker ratio for increased lift, it's likely the guide boss will have to be shortened to provide sufficient clearance between it and the bottom of the spring retainer, this is done before machining for the stem seal. Another option is a longer stem valve, this of course adds complication of a longer spring, relocated rocker arms, longer puhsrods, thicker dia rocker studs, rocker girdle, taller rocker covers and so on.

- After the guide boss has been machined for spring and retainer clearance, if there's anything of them left, they can be machined for positive stem seals. Also, you're gonna love this; the thickness of the stem seal has to be figured into how far the boss has to be cut down for retainer clearance.

Bogie
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