Piston Replacement
12-03-2009, 01:56 PM
#21
Cylinders 1-3 displace 499.35cc, #4 being +.25mm would displace 502.22cc, +0.6% more. So if cylinders 1-3 are running at 12.5:1 A/F, cylinder 4 will be at 12.4:1.
IMO the bigger concern is that the piston set might have been matched from the factory (i.e., they might sort groups of 4 by weight), so putting in an odd one might put it out of spec by a smidge. I still wouldn't expect it to be a problem. I'd be tempted to do #4 only.
But I'd be much more tempted to just get a 2.2 bottom end for it!
IMO the bigger concern is that the piston set might have been matched from the factory (i.e., they might sort groups of 4 by weight), so putting in an odd one might put it out of spec by a smidge. I still wouldn't expect it to be a problem. I'd be tempted to do #4 only.
But I'd be much more tempted to just get a 2.2 bottom end for it!
12-03-2009, 02:22 PM
#22
There is the ideal world or unlimited budgets and identical specifications, then the is the real world of limited budgets and what works in real life.
As I said before, if you are on a budget just replace the one piston. Just make sure you balance them on a set of accurate scales. I'm pretty sure you are going to find the other 3 are just as different weights to the new +0.25mm piston.
Make sure they use a diamond hone to increase the bore size exactly as per the service manual requirements. Only use a workshop who had done alloy/FRM style blocks before.
To balance out the weights I use a die grinder to carefully remove material off the solid pin bosses, or there are no obvious lumps to machine back, then I thin out the inside of the skirts.
If budget isnt a concern, then either a new short block or 4 new pistons will give you virgin bores/clearances on all cylinders.
As I said before, if you are on a budget just replace the one piston. Just make sure you balance them on a set of accurate scales. I'm pretty sure you are going to find the other 3 are just as different weights to the new +0.25mm piston.
Make sure they use a diamond hone to increase the bore size exactly as per the service manual requirements. Only use a workshop who had done alloy/FRM style blocks before.
To balance out the weights I use a die grinder to carefully remove material off the solid pin bosses, or there are no obvious lumps to machine back, then I thin out the inside of the skirts.
If budget isnt a concern, then either a new short block or 4 new pistons will give you virgin bores/clearances on all cylinders.
12-03-2009, 03:59 PM
#23
Registered User
Keep in mind that a new shortblock includes new crank, rods, bearings, etc. as well as pistons and block casting. Balanced and assembled to factory specs.
If you can get one for a good price, that's probably the way to go. Unless you want to build a low-compression engine for boosting or want to increase the displacement.
If you can get one for a good price, that's probably the way to go. Unless you want to build a low-compression engine for boosting or want to increase the displacement.
12-03-2009, 10:09 PM
#24
Originally Posted by ZDan,Dec 4 2009, 12:56 AM
Cylinders 1-3 displace 499.35cc, #4 being +.25mm would displace 502.22cc, +0.6% more. So if cylinders 1-3 are running at 12.5:1 A/F, cylinder 4 will be at 12.4:1.
BTW, how many mileage has your engine, hippos2k?
Depending on that it can be usefull to replace all pistons. But if it hasn't run too many miles, a replacement of only the damaged piston with an oversized (87.25mm) is absolutly reliable and no unusual procedure. Just do the balancing as Chris mentioned.
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