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Topic Review (Newest First)
04-25-2008 09:46 PM
Johnunit Bogie, I envy you for the fact that you just put "more fun than " and "small block ford datsun z car" in the same sentence. Sounds like a hell of a life.
04-25-2008 09:10 PM
BogiesAnnex1
Quote:
Originally Posted by sprecher48
Bogie; I couldn't have said it better my self,but then again,you obviously know more on this than i do(most of my experience is with imports) GOOD POST!!! Tom Do you by any chance teach?
No actually, I'm an airplane design engineer. Used to have a shop with a friend in San Diego a few decades back that specialized in American engine and driveline conversions for high end imports back when MB, Jag, etc didn't have the quality they do today. We did other more funner stuff but SBCs/BBCs in Jags and Benzes, SBFs into Volvos and Datsun Z cars paid the bills. A divorce ended that, so I got a regular job in Seattle, but keep a hand in with a few swaps, the occasional custom kit, and a couple chopper projects. When I retire, which is overdo, first thing I'm gonna do is 4 Corners on a chopper, finish the damn homebuilt airplane that never gets done, and I'm itching to drop an LS something or other 'Vette engine and driveline into a late 40s early 50s Chev/GMC or Ford pickup. My wife would be happier if I took up a rocking chair, so I was wondering if I could fit a 350 with a rocking crank under one.

My present wife had a few kids and we had a few more, plus she raised wolves. Between the kids and the wolves, I got used to stepping in to squabbles. The wolves are easier, when you bust mr. and mrs. alpha in the chops, they and everybody else realizes your in charge and treat you with do respect. The kids are slower learners.

Bogie
04-25-2008 07:55 PM
sprecher48
re;what you can look for

Quote:
Originally Posted by oldbogie
OK kids, before we all get into trouble lets look at this thing to see where it can go wrong:

I wrote that before the blog got closed, that'll learn everbody, no desert and finish your peas or you'll have 'em at breakfast.

Darkspaun, just some thoughts that you'll have to take a look at. One thing from the time you're a novice engine builder to the time you're a pro, you'll be bit by something you didn't plan for more than once. We can move this off line if you want, but here's my top level view of where your at with this thing.

First, the crank is in and spins, this is a good sign that the mains are pretty straight and the clearances are at least adequate. So this isnít a problem.

Second, as the pistons and rods are connected up the crank ceases to turn. This is a point where it usually gets hard to turn but not impossible. The list of things that can go wrong at this point is pretty long, so letís see if we can peel it apart. In this area race engines are usually easier to turn over because of looser tolerances, street engines can be harder sometimes a lot harder because they're usually put together pretty tight trading power for longevity. Different shops take different approaches.

Starting at disassembly, if the rod shanks and caps were not numbered, then the person doing the disassembly needs to mark them, convention has the marks facing down such that they can be read when the pan is removed. The factory usually does this but not always. In the case of the split pin crank where the rod and cap need a chamfer on both sides, orientation with the configuration of the rod journal isnít a concern so itís common to find these rods un-numbered. However, rods shanks and caps still need to align properly for insert tang position and orientation of the cap to the shank for alignment purposes thru the bolts. So this is something that needs to be looked for upon disassembly. Still if itís missed, at assembly one can figure out what goes where by cut and try one at a time to see which pieces fit together the best.

Pistons need to be assembled to the rods in such a way that the piston which has some sort of index which points toward the front of the engine is aligned properly with the rod as it would be installed. Pistons typically come with a pin offset toward the thrust side to reduce skirt slap against the wall when the direction of movement in the bore is reversed. If this is backwards the engine will run fine but will have a tick every time each piston reverses direction. Years ago racers did this intentionally as it reduces a small frictional loss between the piston skirt and the cylinder wall.

If for some reason the rod bearing to journal clearance is too tight and is the source of a clamping action on the crank, thus preventing rotation. You can test for this simply by tightening the rods on their journals from the bottom without putting the pistons in their bores to see if anyone pulls up tight enough to bind.

The piston and ring set binding is a strong possibility. First the piston and ring set and the cylinder wall need to be reasonably oiled. Assembled dry they can generate enough resistance to stop rotation. So first off is to be sure this isnít going together dry.
Next stop is piston to wall clearance. Something in the range of .004 is good for a cast piston maybe twice that for a forging. Are the bores finished to a standard oversize or was the ridge reamed and glaze broken? The latter process isnít very good and typically leads to a very stiff engine upon reassembly. Rings, check the size bore theyíre made for against the bore you have, a good check is to put them in the bore theyíll work in one at a time, square them with the piston and check the end gap, there has to be some. Youíre also looking for bending or torquing of the ring because a ring that is too big for the bore will be binding even if somebody put the correct end gap into it. Once installed on the piston and pushed into the bore a binding ring will stop motion instantly. The rings also need a clearance in the vertical between themselves and the land they are in. They also need a clearance to the back of the land. You should be able to flex the ring far enough into the land that without its natural springiness it wouldnít contact the cylinder wall at all. You also want to see freedom in wrist pin to piston movement; the piston should flop on the rod but not with a discernable looseness between the pin and its bore.

If you have to take the pistons off the rods it probably means at the least youíll need a new set of pins. This is a high force process that usually marks the pin and often breaks the piston. So donít entertain this unless you know for sure thereís an orientation problem. It does happen; good shops have gotten this wrong more than once.

As you put it together keep roatating it as each cylinder's parts are installed, this gives you a feel for how stiff its getting by cylinder and will tell you if any one in particular is a causing a problem.


Bogie
Bogie; I couldn't have said it better my self,but then again,you obviously know more on this than i do(most of my experience is with imports) GOOD POST!!! Tom Do you by any chance teach?
04-25-2008 06:48 PM
Steel This is my first post and I'm going to use it to say, "very good post"!!
04-25-2008 05:18 PM
BogiesAnnex1
What you gotta look for with a "Fresh motor wont turn over..."

OK kids, before we all get into trouble lets look at this thing to see where it can go wrong:

I wrote that before the blog got closed, that'll learn everbody, no desert and finish your peas or you'll have 'em at breakfast.

Darkspaun, just some thoughts that you'll have to take a look at. One thing from the time you're a novice engine builder to the time you're a pro, you'll be bit by something you didn't plan for more than once. We can move this off line if you want, but here's my top level view of where your at with this thing.

First, the crank is in and spins, this is a good sign that the mains are pretty straight and the clearances are at least adequate. So this isnít a problem.

Second, as the pistons and rods are connected up the crank ceases to turn. This is a point where it usually gets hard to turn but not impossible. The list of things that can go wrong at this point is pretty long, so letís see if we can peel it apart. In this area race engines are usually easier to turn over because of looser tolerances, street engines can be harder sometimes a lot harder because they're usually put together pretty tight trading power for longevity. Different shops take different approaches.

Starting at disassembly, if the rod shanks and caps were not numbered, then the person doing the disassembly needs to mark them, convention has the marks facing down such that they can be read when the pan is removed. The factory usually does this but not always. In the case of the split pin crank where the rod and cap need a chamfer on both sides, orientation with the configuration of the rod journal isnít a concern so itís common to find these rods un-numbered. However, rods shanks and caps still need to align properly for insert tang position and orientation of the cap to the shank for alignment purposes thru the bolts. So this is something that needs to be looked for upon disassembly. Still if itís missed, at assembly one can figure out what goes where by cut and try one at a time to see which pieces fit together the best.

Pistons need to be assembled to the rods in such a way that the piston which has some sort of index which points toward the front of the engine is aligned properly with the rod as it would be installed. Pistons typically come with a pin offset toward the thrust side to reduce skirt slap against the wall when the direction of movement in the bore is reversed. If this is backwards the engine will run fine but will have a tick every time each piston reverses direction. Years ago racers did this intentionally as it reduces a small frictional loss between the piston skirt and the cylinder wall.

If for some reason the rod bearing to journal clearance is too tight and is the source of a clamping action on the crank, thus preventing rotation. You can test for this simply by tightening the rods on their journals from the bottom without putting the pistons in their bores to see if anyone pulls up tight enough to bind.

The piston and ring set binding is a strong possibility. First the piston and ring set and the cylinder wall need to be reasonably oiled. Assembled dry they can generate enough resistance to stop rotation. So first off is to be sure this isnít going together dry.
Next stop is piston to wall clearance. Something in the range of .004 is good for a cast piston maybe twice that for a forging. Are the bores finished to a standard oversize or was the ridge reamed and glaze broken? The latter process isnít very good and typically leads to a very stiff engine upon reassembly. Rings, check the size bore theyíre made for against the bore you have, a good check is to put them in the bore theyíll work in one at a time, square them with the piston and check the end gap, there has to be some. Youíre also looking for bending or torquing of the ring because a ring that is too big for the bore will be binding even if somebody put the correct end gap into it. Once installed on the piston and pushed into the bore a binding ring will stop motion instantly. The rings also need a clearance in the vertical between themselves and the land they are in. They also need a clearance to the back of the land. You should be able to flex the ring far enough into the land that without its natural springiness it wouldnít contact the cylinder wall at all. You also want to see freedom in wrist pin to piston movement; the piston should flop on the rod but not with a discernable looseness between the pin and its bore.

If you have to take the pistons off the rods it probably means at the least youíll need a new set of pins. This is a high force process that usually marks the pin and often breaks the piston. So donít entertain this unless you know for sure thereís an orientation problem. It does happen; good shops have gotten this wrong more than once.

As you put it together keep roatating it as each cylinder's parts are installed, this gives you a feel for how stiff its getting by cylinder and will tell you if any one in particular is a causing a problem.


Bogie

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