how to i.d a rebuild
#1
11-25-2014, 08:57 PM
how to i.d a rebuild
i bought a f150 1975 with rebuilt 351m,
but i have no details on the build my questions are.
1)What is the norm for a rebuilt usually ?
2) The engine is a 2b no headers so stock rebuild? but it would have to be bored out right ?
3) Is their a way to tell what work has been done with out ripping the engine apart?
I know i proly will not now for sure. looking for basics.
thank`s Will
but i have no details on the build my questions are.
1)What is the norm for a rebuilt usually ?
2) The engine is a 2b no headers so stock rebuild? but it would have to be bored out right ?
3) Is their a way to tell what work has been done with out ripping the engine apart?
I know i proly will not now for sure. looking for basics.
thank`s Will
#2
11-26-2014, 07:13 AM
Posting Legend
See below, in red. But, the 351M is a hard engine to rebuild as few pistons are available to give you even the miserable stock compression ratio, and none are available to give you good compression ratio.
i bought a f150 1975 with rebuilt 351m,
but i have no details on the build my questions are.
1)What is the norm for a rebuilt usually ?i don't understand the question. But, I'll hazard this: A normal rebuild will put the engine back as close to stock as is possible. This would include grinding the crank undersized to make the bearing surfaces round again, resizing the rods so their openings are round, boring the block to get the bores get them round, and installing new pistons, rings, timing gears and chain, and all new gaskets.
2) The engine is a 2b no headers so stock rebuild? but it would have to be bored out right ? The engine should be bored out for a proper rebuild as cylinders don't wear round. But some people try to get by with honing it, which won't return the bore to truly round and the new rings will not properly seat then.
3) Is their a way to tell what work has been done with out ripping the engine apart? Not really. To determine if a good rebuild has been done you would have to pull the heads and pull the pan. With the head off and a bore gauge or depth mike you can figure out if the block was bored. And with the pan off you can check that the main and rod bearings are sized properly and you can measure the crank throws to see if they are round.
I know i proly will not now for sure. looking for basics. no, you probably won't know.
thank`s Will
but i have no details on the build my questions are.
1)What is the norm for a rebuilt usually ?i don't understand the question. But, I'll hazard this: A normal rebuild will put the engine back as close to stock as is possible. This would include grinding the crank undersized to make the bearing surfaces round again, resizing the rods so their openings are round, boring the block to get the bores get them round, and installing new pistons, rings, timing gears and chain, and all new gaskets.
2) The engine is a 2b no headers so stock rebuild? but it would have to be bored out right ? The engine should be bored out for a proper rebuild as cylinders don't wear round. But some people try to get by with honing it, which won't return the bore to truly round and the new rings will not properly seat then.
3) Is their a way to tell what work has been done with out ripping the engine apart? Not really. To determine if a good rebuild has been done you would have to pull the heads and pull the pan. With the head off and a bore gauge or depth mike you can figure out if the block was bored. And with the pan off you can check that the main and rod bearings are sized properly and you can measure the crank throws to see if they are round.
I know i proly will not now for sure. looking for basics. no, you probably won't know.
thank`s Will
#3
11-27-2014, 05:32 AM
. X 2... on what Gary said...
. But the term 'rebuild' is slung around loosely and can be anything from:
. a 'lie'... nothing was actually done... they just said that to sell the engine/vehicle...
. a 'repair' and/or 'going through'... engine partially to completely disassembled and any parts no longer functional replaced...
. a 'rebuild'... a re-hone or re-bore & re-hone... some parts replaced with new at the discretion of the rebuilder as to just how many... some parts with expected long service life still in them may be left re-used as is...
. a 're-manufacture'... all parts subject to wear re-surfaced or replaced with new whether they were still usable or not... expected to give same service life as a brand new engine... (except today many new parts may have been made in China and of poor quality and won't last as long as re-used original parts, so many like to repair/rebuild their own engines using parts of known manufacture/quality)
. As Gary correctly points out, 'rebuilder' pistons for a 351M these days usually even lower compression ratio ( mid 7's) than original pistons (high 7's (claimed low 8's) )and, thus, rebuilt engine has even less power than it had originally...
. Also, the cams in these 1970's engines had retarded timing at the timing chain/sprockets (from that used in 1960's) for emissions reasons that also hurts power...
. What are your suspicions about the engine? A simple external test using an inexpensive compression tester can give some clues as to your engine's condition... (might be able to borrow a tester for free from a local auto parts store or car enthusiast by leaving a security deposit)...
. All 351M's and most or all 400's came with 2 bbl. carb... carb. not usually part of an "engine rebuild" unless the customer asked for a new or rebuilt one... neither are other external parts such as fuel pump, intake and exhaust manifolds, filters, air cleaner, exhaust system, computer, EGR, air tubes, etc... the engine re-installer usually always uses a new oil filter, though... and a new air filter element...
. But the term 'rebuild' is slung around loosely and can be anything from:
. a 'lie'... nothing was actually done... they just said that to sell the engine/vehicle...
. a 'repair' and/or 'going through'... engine partially to completely disassembled and any parts no longer functional replaced...
. a 'rebuild'... a re-hone or re-bore & re-hone... some parts replaced with new at the discretion of the rebuilder as to just how many... some parts with expected long service life still in them may be left re-used as is...
. a 're-manufacture'... all parts subject to wear re-surfaced or replaced with new whether they were still usable or not... expected to give same service life as a brand new engine... (except today many new parts may have been made in China and of poor quality and won't last as long as re-used original parts, so many like to repair/rebuild their own engines using parts of known manufacture/quality)
. As Gary correctly points out, 'rebuilder' pistons for a 351M these days usually even lower compression ratio ( mid 7's) than original pistons (high 7's (claimed low 8's) )and, thus, rebuilt engine has even less power than it had originally...
. Also, the cams in these 1970's engines had retarded timing at the timing chain/sprockets (from that used in 1960's) for emissions reasons that also hurts power...
. What are your suspicions about the engine? A simple external test using an inexpensive compression tester can give some clues as to your engine's condition... (might be able to borrow a tester for free from a local auto parts store or car enthusiast by leaving a security deposit)...
. All 351M's and most or all 400's came with 2 bbl. carb... carb. not usually part of an "engine rebuild" unless the customer asked for a new or rebuilt one... neither are other external parts such as fuel pump, intake and exhaust manifolds, filters, air cleaner, exhaust system, computer, EGR, air tubes, etc... the engine re-installer usually always uses a new oil filter, though... and a new air filter element...
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