So my son purchased a buick 350 to replace the olds 350 the previous owner had installed in his 67 skylark. As it turns out the buick 350 is dated 1969 rp code which was the 280 hp high compression 10.25.1 my mechanic he purchased it from said the motor ran surprisingly strong before he pulled it from a 52 GMC pickup he is doing an ls swap on. Anyhow long story short we camera scoped the cylinders and he feels the motor has never been apart and by looking at the pistons they have just a slight dish to them. Not as much of a dish that TA shows on their replacement pistons. Just wondering where the stock pistons dished or flat top or does anyone have a pic? Thanks Kirk
This is the original piston removed from a 1972 350. The 72 engines were rated at 8.5:1. Your piston should have a shallower dish.
They are not dished near that much it's very shallow and the dimple from being cast is I would say for sure less than half as tall as the one pictured from the 72 they are slightly raised. Would the stock pistons from the 69 have a small dimple or nipple because they were still a cast piston? What's your opinion Larry? And thanks for your responses from my previous post on this motor!
All stock pistons are cast. As hugger stated, your compression won't be 10.25:1. It will be 9. something.
I believe the consensus is that even thought Buick promoted the static compression ratio of these engines as 10.25:1 The actual compression (even if the engine is still stock) will be less? I am sure I will be corrected if that's not the point ;~)
This is a 71 low compression and a 70 hi compression piston. Roughly 24 cc vs 10 cc . With a flel pro head gasket (.040)and .058 below deck both pistons seem to measure, the hi compression is about 9.2.
Wow that's wild. Well this post did confirm this motor still has the stock style pistons. In comparison with the 70 piston its a match. Pretty wild 52 year old motor.
That's for sure it definitely could have been honed and re ringed at some point in the last 52 years. I guess just dont know.
If trying to do a budget build of course you could mill the heads to up the compression & hone/re-ring/new bearings. Did that to my '69 400 as a kid and it ran great - Drove for years & sold as a runner. Never any issue w/the extra piston/wall clearance (file fit the rings).
Personally I would measure the piston depth below deck height, and mill the block to get zero deck. Then 40 thousand pistons and TA alum heads. With the right camshaft it would be a monster.
I'm always thinking orig. #'s in suggesting milling the heads but in this case you're correct as it doesn't matter & that's probably the better approach to upping the CR.
Whatever the Hell you do with any used Pistons be they cast or forged during a rebuild DO NOT , once again DO NOT do any glass beading or any kind of grit blasting to the ring lands! If you do the motor once is reassembled it will burn added oil since the fine pitting on the machined ring groove flats from the grit blasting impeades the ring seal and lowers cylinder pressure. If you take your used motor parts to a shop for glass beading make dam sure that they will not do this procedure on your Pistons!! The piston shown in post number 4 looks to me like it was glass beaded, and on top of that it looks like the normal acid that get produced as part of the combustion process has eaten away at the ring lands also, so this piston to me is well on its way to just being a paper weight or good for use only in a around town food store motor. With any used piston going in a street if the ring groove clearance is more then .003" the motor will be down on power from what it could be making and in terms of a race motor you want that number to not exceed.002". Also when reusing Pistons, especially factory ones make sure the the oil ring drain grooves or holes are all clear,as this is a big reason why some rebuild motors oil consumption is really good until the motor gets above 3500 rpm and then it all goes to Hell since that oil ring groove can't drain out fast enough and the PCV system is overwhelmed.
I personally wouldn’t reuse a stock cast piston. Replacements aren’t that expensive compared to the time lost having to do it again. Just my .02
Steve, that is an original piston out of my first Buick. A 1972 Buick Skylark 350. I rebuilt the motor at 200K, and then drove the car another 50K. I had the machine shop clean up that one piston for me to keep. Trust me, it will never see the inside of a motor again.. It's been sitting on my coffee table for the last 30 years.
