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Old 05-02-2007, 04:14 AM   #1
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Default Back plate clearance ???

Hope i get some good advice with regards to what is ideal ,best or worst for .12 engine back plate clearance.
Do we want a fair bit of clearance or as little as possible ???
Ive seen some back plates have the con rod rubbing them ,im sure this cant be good.
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Old 05-02-2007, 05:39 AM   #2
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it is, what it is.....
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Old 05-02-2007, 07:40 AM   #3
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Quote:
Originally Posted by razzor
Hope i get some good advice with regards to what is ideal ,best or worst for .12 engine back plate clearance.
Do we want a fair bit of clearance or as little as possible ???
Ive seen some back plates have the con rod rubbing them ,im sure this cant be good.
Razzor, i have seen 3 Nova LS3 engines now , including my own. when the bearings wear, the inward outward movement in the crank is causing the conrod to rub on the back plate. this is causing a problem with trying to tune the engine in a false manner. its ok when cold but when at temps the tune becomes erratic and feels as though it hasnt enough fuel. so you richen it up, and then it bogs down. thing is to get on to replacing the bearings fairly quickly as this can cause a motor failure. the conrod can move that much and cause extra heat and wear. the front bearing starts to run on the alloy of the block, and fuel leakage is evident from the front bearing.
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Old 05-02-2007, 08:43 AM   #4
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Check out the backplate of the new 353 engines and you will find your solution for that problem,you will just need a good lathe to modify your backplate...
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Old 05-02-2007, 08:55 AM   #5
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Originally Posted by Pattojnr
Razzor, i have seen 3 Nova LS3 engines now , including my own. when the bearings wear, the inward outward movement in the crank is causing the conrod to rub on the back plate. this is causing a problem with trying to tune the engine in a false manner. its ok when cold but when at temps the tune becomes erratic and feels as though it hasnt enough fuel. so you richen it up, and then it bogs down. thing is to get on to replacing the bearings fairly quickly as this can cause a motor failure. the conrod can move that much and cause extra heat and wear. the front bearing starts to run on the alloy of the block, and fuel leakage is evident from the front bearing.
even on a brand spankin' new engine there is fore/aft crank play, or else the crank pin would already be hitting the backplate. Does that mean the bearings are bad from the factory?? These parts are batch produced, slapped together, and vary from engine to engine.... even of the same type.

Crank pins and journal widths have a tolerance, blocks have a bearing bore depth tolerance, rods have a width tolerance, backplates have a depth tolerance, etc.... stack them all up in the right direction and you have more play in one engine than the next engine.
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Old 05-02-2007, 09:59 PM   #6
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Quote:
Originally Posted by cdelong
even on a brand spankin' new engine there is fore/aft crank play, or else the crank pin would already be hitting the backplate. Does that mean the bearings are bad from the factory?? These parts are batch produced, slapped together, and vary from engine to engine.... even of the same type.

Crank pins and journal widths have a tolerance, blocks have a bearing bore depth tolerance, rods have a width tolerance, backplates have a depth tolerance, etc.... stack them all up in the right direction and you have more play in one engine than the next engine.
what i meant was when the clutch is on the engine.
i have replaced the bearings and there has been no movement after the new bearings.
at no time did i ever say the bearings were no good from the factory. did i ?
i have just stated mt experience with this. the 3 engines were fixed with new bearings. all of them had about 7 or 8 lts of fuel through them.
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Old 05-03-2007, 12:35 AM   #7
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so i guess after fitting a new engine with a flywheel everything is ok but as engine runs over time the bearing developes play hence crank play.
So its also a sign of bearing going bad .
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Old 05-03-2007, 02:10 AM   #8
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Quote:
Originally Posted by razzor
so i guess after fitting a new engine with a flywheel everything is ok but as engine runs over time the bearing developes play hence crank play.
So its also a sign of bearing going bad .
thats it. it happened suddenly as well. i had run one meet faultless all weekend. the next weekend it wasnt the same, and had problems from then on. since the new bearings, its been fine in testing.
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