Cylinder Bore Scratches Opinion - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Moore · 04-29-2014, 10:04 AM

Looking for the opinion of someone who may have built a couple motors.

Here are the pictures. I did not see these scratches until I got the block back from the machine shop.

You can see a couple small scratches, these are in cylinder 3 only. I can lightly catch a finger nail on 2 of them, they are not very long but would likely touch the top compression ring. The shop took measurements, cleaned and deglazed the cylinder. The guy is telling me that the scratches were present before they worked on it, but in his opinion he did not think boring was required and if it was his own motor he would have done the same. Of course he's telling me if I am concerned bring it back and they will bored it out. The other pia part is I already purchased piston's to stock size when he told me the bore checked out okay. So should I spend the money to get it bored and deal with trying to return/exchange the pistons or leave it be?

blueshark123 · 04-29-2014, 10:42 AM

What are you trying to do with motor? What motor also?

Moore · 04-29-2014, 10:47 AM

sr20

Just a mild rebuild, car is a daily driver not pushing huge hp numbers.

waxball88 · 04-29-2014, 11:20 AM

This is curious. IF stock bore pistons fit after bore, it is probably at a loose tolerance and more honing would make it even looser.
I just went through this, bought a motor already built stock bore pistons, light scratch in cyl 1 wall. Mechanist said i was looking at 4-4.5 piston/wall clearance after hone. CP said 3-3.5 is ideal. At 4.5 to expect piston slap aka the motor be noisey which in my terms means a shorter service life. They said for my goals of 600whp this clearance is doable.
So i brought a second stock block in seeming good shape and was looking at 5 p/w clearance, so even worse than the first.
Ended up buying 20 over pistons and will be using block #1 with the appropriate clearance.

Moral of the story, just buy 20 over pistons.
Bigger pistons can fit in just about any block you can find, but not visa-verse

However, in your case, the best bet is to contact the manufacturers of the pistons and see what clearances they accept, then get numbers from the machine shop. If you are within spec, get the hone, if you aren't....well its up to you, shorter service life or get bigger pistons.

Moore · 04-29-2014, 12:19 PM

I'm not sure what the clearance's are exactly but I would assume you are correct as they would have had to take a bit of material off when they deglazed and rehoned. If I do take it back I will be going up in piston size but like I said I would like pass on the cost and burden to exchange the pistons if I had feed back in that direction.

Right now the feedback is fairly mixed, I'm going to measure how far the scratch goes down the cylinder tonight and verify it will actually contact with the ring. If it does I'll most likely bore and go with larger pistons, if it doesn't then I don't think it really has any affect.

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04-29-2014, 10:04 AM	#1
Moore Leaky Injector Join Date: Nov 2004 Location: toronto Posts: 67 Trader Rating: (0) Feedback Score: 0 reviews	Cylinder Bore Scratches Opinion Looking for the opinion of someone who may have built a couple motors. Here are the pictures. I did not see these scratches until I got the block back from the machine shop. You can see a couple small scratches, these are in cylinder 3 only. I can lightly catch a finger nail on 2 of them, they are not very long but would likely touch the top compression ring. The shop took measurements, cleaned and deglazed the cylinder. The guy is telling me that the scratches were present before they worked on it, but in his opinion he did not think boring was required and if it was his own motor he would have done the same. Of course he's telling me if I am concerned bring it back and they will bored it out. The other pia part is I already purchased piston's to stock size when he told me the bore checked out okay. So should I spend the money to get it bored and deal with trying to return/exchange the pistons or leave it be?

04-29-2014, 10:42 AM	#2
blueshark123 Post Whore! Join Date: Apr 2006 Location: North Jersey Posts: 5,481 Trader Rating: (55) Feedback Score: 55 reviews	What are you trying to do with motor? What motor also?

04-29-2014, 10:47 AM	#3
Moore Leaky Injector Join Date: Nov 2004 Location: toronto Posts: 67 Trader Rating: (0) Feedback Score: 0 reviews	sr20 Just a mild rebuild, car is a daily driver not pushing huge hp numbers.

04-29-2014, 11:20 AM	#4
waxball88 Zilvia FREAK! Join Date: Jun 2009 Location: Gainesville Posts: 1,061 Trader Rating: (9) Feedback Score: 9 reviews	This is curious. IF stock bore pistons fit after bore, it is probably at a loose tolerance and more honing would make it even looser. I just went through this, bought a motor already built stock bore pistons, light scratch in cyl 1 wall. Mechanist said i was looking at 4-4.5 piston/wall clearance after hone. CP said 3-3.5 is ideal. At 4.5 to expect piston slap aka the motor be noisey which in my terms means a shorter service life. They said for my goals of 600whp this clearance is doable. So i brought a second stock block in seeming good shape and was looking at 5 p/w clearance, so even worse than the first. Ended up buying 20 over pistons and will be using block #1 with the appropriate clearance. Moral of the story, just buy 20 over pistons. Bigger pistons can fit in just about any block you can find, but not visa-verse However, in your case, the best bet is to contact the manufacturers of the pistons and see what clearances they accept, then get numbers from the machine shop. If you are within spec, get the hone, if you aren't....well its up to you, shorter service life or get bigger pistons.

04-29-2014, 12:19 PM	#5
Moore Leaky Injector Join Date: Nov 2004 Location: toronto Posts: 67 Trader Rating: (0) Feedback Score: 0 reviews	I'm not sure what the clearance's are exactly but I would assume you are correct as they would have had to take a bit of material off when they deglazed and rehoned. If I do take it back I will be going up in piston size but like I said I would like pass on the cost and burden to exchange the pistons if I had feed back in that direction. Right now the feedback is fairly mixed, I'm going to measure how far the scratch goes down the cylinder tonight and verify it will actually contact with the ring. If it does I'll most likely bore and go with larger pistons, if it doesn't then I don't think it really has any affect.