Do I need to over-bore my block?
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
Do I need to over-bore my block?
I am rebuilding my engine in my 1980.
I have measured the cylinder bores and they are between 4.001” and no more than 4.004”, however some of the cylinders have vertical scratches in the bores them self.
Do I need to over-bore my block or can I just replace my rings?
Thank you
I have measured the cylinder bores and they are between 4.001” and no more than 4.004”, however some of the cylinders have vertical scratches in the bores them self.
Do I need to over-bore my block or can I just replace my rings?
Thank you
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
can you feel a ridge with your finger nail? In your opinion could you hone out the scratches? Was that caused by the piston pin?
I'm a firm believer in blue printed motors. Where everything is machined square and align bored on the cam and crank shaft. Balanced motors also gives extra hp.
I'm a firm believer in blue printed motors. Where everything is machined square and align bored on the cam and crank shaft. Balanced motors also gives extra hp.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
[QUOTE]
No I can not feel a ridge.
This is a picture of one of the pistons and as you can see the side of the piston is worn out.
This means that the side of the piston and cylinder wall were touching each other and wearing out.?
This is a picture of one of the pistons and as you can see the side of the piston is worn out.
This means that the side of the piston and cylinder wall were touching each other and wearing out.?
Melting Slicks
Joined: May 2006
Posts: 3,438
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From: Raleigh NC
St. Jude Donor '13-'14
The skirt didnt' cause that scratching. Look at the orientation: scratches are north/south, the skirt sits east west.
Last edited by LeMans Pete; Nov 22, 2008 at 09:31 AM.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
[QUOTE] Once very,very,very badly in stop and go traffic. Oil pressure dropped down to 15 psi and smoke pored out of the exhaust pipes, but the coolant was still no more than 220F.
I switched the engine off and let it cool down for a long time.
Restarted the engine and it seemed ok.
I switched the engine off and let it cool down for a long time.
Restarted the engine and it seemed ok.
Melting Slicks
Joined: May 2006
Posts: 3,438
Likes: 41
From: Raleigh NC
St. Jude Donor '13-'14
Once very,very,very badly in stop and go traffic. Oil pressure dropped down to 15 psi and smoke pored out of the exhaust pipes, but the coolant was still no more than 220F.
I switched the engine off and let it cool down for a long time.
Restarted the engine and it seemed ok.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Suggest you have a trusted local machine shop check it. I do NOT know how or with what gages you're measuring ... but MOST novice folks do Not have good technique nor good gages. You may be a Pro with Pro tools, I dunno.
Keep in mind ... forged pistons require more clearance than do cast & hyper.
I can't say with certainty because of pic ... but seems more likely than not your piston is cast. Sharp pic of INSIDE/Underhead of piston will usually confirm.
After looking at pics, I don't know anyone who could say with certainty if your cylinder needs boring. But ... it don't look very good to me. And ... more often than not, an old 350 will need boring.
If you're gonna keep car, suggest you bore it ... even rebuild it as a cheap & simple 383.
Keep in mind ... forged pistons require more clearance than do cast & hyper.
I can't say with certainty because of pic ... but seems more likely than not your piston is cast. Sharp pic of INSIDE/Underhead of piston will usually confirm.
After looking at pics, I don't know anyone who could say with certainty if your cylinder needs boring. But ... it don't look very good to me. And ... more often than not, an old 350 will need boring.
If you're gonna keep car, suggest you bore it ... even rebuild it as a cheap & simple 383.
Last edited by jackson; Nov 22, 2008 at 09:57 AM.
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Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Is that an L-82 motor? If it is I'd just buy some forged flat top pistons, total seal rings, balance the rotating assembly, and a Crane 272 Powermax cam kit
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
Can I go with just 0.010 or do I need to go all the way to 0.030
Engine is standard L48 with 60XXX-ish miles and I belive to be true miles.
Dial Bore Gauge is 0.0005" grad. to 0.025"
Last edited by C3Paul; Nov 22, 2008 at 10:12 AM.
Melting Slicks
Joined: Mar 2008
Posts: 2,989
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From: Meriden CT
Your machine shop can tell you how much they need to go. Good gage by the way. Nice to see someone who can use one.
Drifting
Joined: Aug 2004
Posts: 1,883
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From: Lubbock TX
I'd have the machinist make a few passes with the hone thru the worst one and go with his advice from there. You can get coated hypereutectic pistons that'll work well and give you less scuffing. If you have to bore it, .020 is the smallest overbore piston I've found.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
[QUOTE]
I have measured this myself and used dial Bore Gauge with 0.0005”-0.025 grad.
I have set the Bore Gauge to 4” in my Micrometer and than reset the Bore Gauge to '0'.
This gave me the measuring range of 4" to 4025".
Rocked the Bore Gauge forward and backwards in different locations and took a long time to measure as accurate as possible.
If there is a technique How To measure Cylinder bore can you explain it to me, please?
In your opinion, what cased the vertical scratches on the walls and pistons?
I have set the Bore Gauge to 4” in my Micrometer and than reset the Bore Gauge to '0'.
This gave me the measuring range of 4" to 4025".
Rocked the Bore Gauge forward and backwards in different locations and took a long time to measure as accurate as possible.
If there is a technique How To measure Cylinder bore can you explain it to me, please?
In your opinion, what cased the vertical scratches on the walls and pistons?
Last edited by C3Paul; Nov 22, 2008 at 10:35 AM.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Without being there and putting my eyes, my hands & gages on it ... I can't tell what caused damage or how bad it is.
It seems wide vertical scrape on cylinder wall is about 90 degrees from thrust face ... So, just a guess that some "dirt" or something that should Not have been there did get in there.
But what does it matter why? .. What matters is how bad it is ... and I agree 110% w/ each & every point said by L88Plus (I'd have the machinist make a few passes with the hone thru the worst one and go with his advice from there. You can get coated hypereutectic pistons that'll work well and give you less scuffing. If you have to bore it, .020 is the smallest overbore piston I've found. )
If you want to hear that you can simply hone it and get away with it ... OK you probably can. But if the bore is wide/tapered etc ... rings won't last very long. If the bore is not so bad then it'll last a long time. I can't say with 100% confidence by looking at some pics ... so I err on side of caution. Hence, get a local Pro auto machinist to check it.
Your technique may be fine ... but I sure ain't gonna write a book on it. Also suggest you have rods checked by Pro for bend/twist. My dial bore gage & mike increment 0.0001" ... but so what ... if it's not used correctly and the whole of the matter viewed in proper context then it matters naught who's got the biggest gun.
It seems wide vertical scrape on cylinder wall is about 90 degrees from thrust face ... So, just a guess that some "dirt" or something that should Not have been there did get in there.
But what does it matter why? .. What matters is how bad it is ... and I agree 110% w/ each & every point said by L88Plus (I'd have the machinist make a few passes with the hone thru the worst one and go with his advice from there. You can get coated hypereutectic pistons that'll work well and give you less scuffing. If you have to bore it, .020 is the smallest overbore piston I've found. )
If you want to hear that you can simply hone it and get away with it ... OK you probably can. But if the bore is wide/tapered etc ... rings won't last very long. If the bore is not so bad then it'll last a long time. I can't say with 100% confidence by looking at some pics ... so I err on side of caution. Hence, get a local Pro auto machinist to check it.
Your technique may be fine ... but I sure ain't gonna write a book on it. Also suggest you have rods checked by Pro for bend/twist. My dial bore gage & mike increment 0.0001" ... but so what ... if it's not used correctly and the whole of the matter viewed in proper context then it matters naught who's got the biggest gun.
Last edited by jackson; Nov 22, 2008 at 11:23 AM.
Le Mans Master
Joined: Sep 2001
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From: Unreconstructed, South Carolina
Gotta go ... wife & I travelling to state capital & museum to see glass art by Dale Chihuly. http://www.columbiamuseum.org/
Last edited by jackson; Nov 22, 2008 at 11:28 AM.
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
If your going to rebuild the motor, do it once, do it right. Getting the block bored is not going to be that much more than honing the cylinders unless you plan on doing it yourself. If it were me get it done correctly 
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 1,136
Likes: 8
From: Chichester, UK
Despite of the fact that the cylinder bores are only worn out by 0.001-0.004” it is recommended to bore the block by 0.020” to clean the bores.
The reason not to bore the block by 0.010” is because the availability and cost of replacement pistons is not cost effective.
Am I right?
Last edited by C3Paul; Nov 22, 2008 at 12:38 PM.