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Old 02-15-2006, 09:51 AM
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Block bored first, THEN bought pistons. Final fitting issues.

Hi Hotrodders,

This is my first post, so be kind!! I am building a SBC for a Jaguar SBC V-8 swap. This is my first car engine rebuild so the forum has been a tremendous resource.

Here is my issue. I pulled a pretty solid SBC from the bone yard and had the decks planed and the cylinders bored +.030. The machinist asked if I had the pistons I was going to use. I didn't but I told him to go ahead and bore it anyway. I have now purchased my pistons, Speed Pro Hyper. The recommended skirt clearance is .001. I am using a .0015 six-inch feeler gauge and some of the cylinders don't quite have that "good" feel. They gauge will slide out with a little tug. Once the feeler gauge is sliding the drag doesn't feel excessive. I just don't like the initial resistance to get it sliding. My question is can I get the necessary clearance by using a flex hone(the one with the little balls)? Can I get it by using a hone with the five-inch stones? Or should I just take it to the machine shop and let them do it?

Any and all opinions are sought. Thanks in advance for the responses. Hopefully future builders can learn from my mistake -buy the pistons first and then take it in.

Ericbr
Minneapolis, MN
Jaguar XJ-S V-12 to V-8

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Old 02-15-2006, 10:03 AM
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If you need .001 and a .0015 is a little tight...What's the problem?

Make sure you are measuring it at the right spot.
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Old 02-15-2006, 10:05 AM
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Use a dial bore guage or "T" guage and mic to measure the bore. Measure the piston with a mic also then compare.

I would take it to where you had the work done. They should measure the clearance for you at no charge.
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Old 02-15-2006, 11:19 AM
 
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Those pistons are to have the clearence checked when measured at the wrist pin center line 90 deg to the pin. Not at the bottom of the skirt. You should mic the pistons there, then use a dial bore gauge to check the clearence. Now days all those pistons should mic the same with in .0002

Piston skirts taper and will have almost no clearence at all at the very bottom of the skirt. This why the feeler gauge feels tight to you.

Sounds like the clearence is right from what you are saying. You might take the block and pistons back to the machine shop and ask to have it all checked.
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Old 02-15-2006, 12:16 PM
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If the machine shop finished honed your bore to .030 over , stick the pistons in and let it rip.
I bore for people all the time and they don't have their pistons, I just finish the oversize at .030-.040-.060 etc.
The finish bore is the oversze that is on the piston , the clerance is built into the piston, so if your don't have a dial bore gauge , feel don't cut it.
Piston Company's have come a long way in producing products that are very close on tolerances.
Now thats my opinion
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Old 02-15-2006, 01:58 PM
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Quote:
Originally Posted by dgcantrellsr
If the machine shop finished honed your bore to .030 over , stick the pistons in and let it rip.
I bore for people all the time and they don't have their pistons, I just finish the oversize at .030-.040-.060 etc.
The finish bore is the oversze that is on the piston , the clerance is built into the piston, so if your don't have a dial bore gauge , feel don't cut it.
Piston Company's have come a long way in producing products that are very close on tolerances.
Now thats my opinion
However there are always going to be quality control issues. Do you really want sealing issues down the road because you didn't take the time to recheck measurements?
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Old 02-15-2006, 02:04 PM
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You are not going to suffer sealing issues at .0005 over. OR even .005 over.
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Old 02-15-2006, 02:12 PM
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Quote:
Originally Posted by dgcantrellsr
If the machine shop finished honed your bore to .030 over , stick the pistons in and let it rip.
I bore for people all the time and they don't have their pistons, I just finish the oversize at .030-.040-.060 etc.
The finish bore is the oversze that is on the piston , the clerance is built into the piston, so if your don't have a dial bore gauge , feel don't cut it.
Piston Company's have come a long way in producing products that are very close on tolerances.
Now thats my opinion

I agree.
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Old 02-15-2006, 03:27 PM
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Quote:
Originally Posted by Siggy_Freud
However there are always going to be quality control issues. Do you really want sealing issues down the road because you didn't take the time to recheck measurements?
What I am saying regarding checking , If you don't have a dial bore gauge, you can't properly check it anyway.
And the rings do the sealing , not the piston.

Freshened a 350 race motor for a friend , it had about 4-5 years of drag racing life, put a .006 feeler gauge in bore and slid piston down bore, fell by gauge , loose , ended up I could put a .015 gauge in bore and push piston by, now that is loose as a goose , customer didn't want to spring for more pistons , put it together with regular .030 race rings and it still went 6.0's at 2100 lbs.
Sometimes stuff will amaze you. Just wish I had kept a log over the years!
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Old 02-15-2006, 04:20 PM
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Quote:
Originally Posted by RPMs
Those pistons are to have the clearence checked when measured at the wrist pin center line 90 deg to the pin. Not at the bottom of the skirt.................
I'm sorry but that info is wrong. Sealed Power Hypers (and most other pistons) are measured near the bottom of the skirt, 90 degrees to the pin centerline. It will say on the piston box exactly where to measure the piston ("Size point xxx from top of head"). Some of the forged SP and others pistons ARE measured at the pin centerline. When in doubt, checke with a machine shop.

If the pistons are coated, the clearance will be pretty much taken up by the coating. They are pretty much designed for the coating to contact the cylinder wall.

The best way to measure the bores is to use a dial bore gauge. The next best way is a well-calibrated inside micrometer. The feeler gauge method is not terribly accurate and has not been recommeded for years.

tom
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Old 02-15-2006, 04:27 PM
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richard stewart 3rd

since this is your first build, I think you should take it back to the shop & ask them to check it for you, also, ask them to show you how to do it, so you'll be able to do it yourself the next time.
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Old 02-15-2006, 07:17 PM
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pistons

I agree with richard. take it to the shop.
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Old 02-15-2006, 07:39 PM
 
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In my newbie opinion, I would definitely take it back to the shop. After going though what your going though, I now let them do everything possible. They do it all day, every day and can fix you up right quick. Make good friends with them and they will take care of you. Good luck!
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Old 02-16-2006, 09:28 AM
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Thanks to all.

Just wanted to thank everybody for their responses. My first post on Hotrodders.com was a positive experience.

I have access to telescoping gages and a micrometer. I will measure the cylinders and pistons and do the math. If things check out within spec, I will go with it.

I was looking for peace-of-mind and the responses have given me that.

Thanks Again,

ericbr
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Old 02-16-2006, 03:37 PM
 
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all is well!!! STUFF'EM AND RUN'EM
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