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Old 04-30-2004, 09:30 PM
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pistons hitting head what now?

Was going to check piston to valve clearance on my bbc 427.Put in piston and rod ,set on head.Turned crank to bring piston up and it hit on head.Pistons are trw l2308af .60.With50cc domes. Did not have head gasket on .backed off head bolts then turned crank .Would lift head up about 30 thousands. Should i get a thick gasket or file a little off piston









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Old 04-30-2004, 09:33 PM
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Determine where the piston is hitting the head. L2308's will hit some heads on the exhaust valve side at the edge of the dome where it joins the flat part of the piston. either blend back part of the piston or open up that part of the head.
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Old 04-30-2004, 09:38 PM
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Cant seem to get the pictures to come up .Its hitting on intake side at bottom .Just a small spot
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Old 04-30-2004, 10:52 PM
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i have seen it where if you had the pistons in backwards they hit the heads on bbc's
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Old 04-30-2004, 11:02 PM
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This may help, I got the pics for ya. ( don't ask how! LOL I'm a regular on the eBay images/HTML board in my off time. Sometimes it pays to be sneeky!~)





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Old 05-01-2004, 12:49 AM
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I've had that problem, just install the head gasket you goober On some engines, the piston will come up to the line of the original head gasket, or it could be your rods are a bit too long, bearings wrong clearence, or bad pitons...

Anyway just install the head gasket and see if it hits, try spraying some paint on the top of the piston to see if the two connect.
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Old 05-01-2004, 08:04 AM
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Quote:
Originally posted by 87442lover
I've had that problem, just install the head gasket you goober On some engines, the piston will come up to the line of the original head gasket, or it could be your rods are a bit too long, bearings wrong clearence, or bad pitons...

Anyway just install the head gasket and see if it hits, try spraying some paint on the top of the piston to see if the two connect.

Bearing clearance is not an issue....not sure where you got that. If the piston is lifting the head .030, then the .040 gasket will not give enough clearance. At least not for my peace of mind. If it is hitting only one the arrow in the picture, I would think you could relieve the chambers a bit to make for good clearance. The picture looks like dome pistons. If so, you could clearance the dome as well. If the piston is coming out of the hole .030, I think I would get a different set of pistons. In this case you either has excessive deck milling or incorrect pin height on the pistons.

Chris
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Old 05-01-2004, 11:11 AM
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Just a word of caution before you start whacking away at the piston make sure there is enough material. Some domes are hallow. I can't tell by the pictures how much needs to be removed. I would probably try to take the material off of the piston if possible.

Make sure you leave enough clearance for rod stretch.

Royce
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Old 05-01-2004, 11:24 AM
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Quote:
Originally posted by camaroman7d
I would probably try to take the material off of the piston if possible.
Royce

Just curious, why the piston and not the head?
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Old 05-01-2004, 11:33 AM
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BstMech,
It really doesn't make much difference. The reason I would cut the piston is because those heads should be around for years after the pistons are shot. So if the next build he decides to go flat top then he would have modified the chamber of the heads and hurt performance. If the pistons are hallow domes there might not be enough meat there to take it off of the piston, in that case I would modify the head. One other thing it is a lot easier to cut aluminum than it is cast iron. In all honesty I would run flat tops anyway (if possible).

Royce
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Old 05-01-2004, 11:10 PM
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Don't you have to cut the same amount from the rest of the pistons too? To keep the balance right? Just curious, not a big block builder.

Mark
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Old 05-01-2004, 11:42 PM
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Quote:
Originally posted by TurboS10
Bearing clearance is not an issue....not sure where you got that
Chris
From experience, swap in a new set of oversized rod bearings and see what happens. If you are doing a fast job, you'll notice it when ya put the piston in and tighten the cap on that the piston now has a bit of an overhang. Don't gripe at me for that, guy gave me the wrong size over the counter. Only took one look to figure it out.
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Old 05-02-2004, 07:14 AM
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Quote:
Originally posted by 87442lover
From experience, swap in a new set of oversized rod bearings and see what happens. If you are doing a fast job, you'll notice it when ya put the piston in and tighten the cap on that the piston now has a bit of an overhang. Don't gripe at me for that, guy gave me the wrong size over the counter. Only took one look to figure it out.
When a crank is ground and oversize bearings are used, the pin centerline does not change. Rod length is measured center of the crank pin to center of the wrist pin........ I am not discounting your experience, but the rod bearings should not change anything.

Now if you are talking about putting an undersize bearing on a standard journal, I think that the rod being locked to the crank after tightening would worry me more

Chris
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Old 05-02-2004, 10:06 AM
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As Turbos10 asked, are the pistons coming out of the hole, or is it just the domes causing the problem? Badknuckes has a good point, as I just completed a bbc 396 for a '67 Chevelle SS, with domes. If I had installed the pistons as common knowledge tells us (numbers up) the domes would not have lined up with the comp chambers. ENSURE YOUR PISTONS ARE INSTALLED CORRECTLY. If they're not, don't simply flip them in the cylinder, you also need to ensure your rods are installed correctly with the tabs (at the rod caps) facing away from each other, to the oustide of the rod journel. It's my experience to always check the simple things first. Keep us informed, let us know what the solution is.

Bill
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Old 05-02-2004, 10:13 AM
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Sorry it took awhile to get back on this. The flat part off the piston is about 20 thousands below deck.Only a small spot on the dome is hitting.Put on a head gasket and still hit, so i took a little off piston and a little off head.Clears it now .How much clearance should i have to allow for rod stretch?Have not checked the rest of the pistons but am sure ill have to grind them all.
Thanks Dennis
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