free rolling motor????
- Thread starter bgr
- Start date
97stscaddy
Dedicated LVC Member
Free rolling? As is non-interference? No these are interference engines AFAIK. When the timing chain breaks valves usually get crashed.
94m5
Dmaup's Daddy
Yes.
cammerfe
Dedicated LVC Member
Valve-piston Crash
I believe this was a topic not too long ago, and so far as I know, it never was answered with certainty. I didn't try to turn over my 4.0 engine after I got it, and even at that, the chains were intact. However, the pistons in a 3.9 are featureless flat tops. The pistons in the 4.0 have very small valve notches just inside the circumference. While broken valve springs might let valves 'come down' far enough to touch, so far as I know, the closest a valve gets to a piston is when the exhaust valve(s) are chasing the piston down the cylinder.
When doing the first bit of research for my engine build, I visited a shop that specializes in rebuilding AJ engines. He had a pile of heads there and none that I saw had 'crashed' valves.
Don't take this as gospel. I haven't SEEN any. That's not quite to say that none exist.
Does anybody have first-hand experience of valve-piston contact?
KS
I believe this was a topic not too long ago, and so far as I know, it never was answered with certainty. I didn't try to turn over my 4.0 engine after I got it, and even at that, the chains were intact. However, the pistons in a 3.9 are featureless flat tops. The pistons in the 4.0 have very small valve notches just inside the circumference. While broken valve springs might let valves 'come down' far enough to touch, so far as I know, the closest a valve gets to a piston is when the exhaust valve(s) are chasing the piston down the cylinder.
When doing the first bit of research for my engine build, I visited a shop that specializes in rebuilding AJ engines. He had a pile of heads there and none that I saw had 'crashed' valves.
Don't take this as gospel. I haven't SEEN any. That's not quite to say that none exist.
Does anybody have first-hand experience of valve-piston contact?
KS
97stscaddy
Dedicated LVC Member
How do you know those heads came from engines that had broken chains, or hadn't been reworked already?
Id like to know for sure as well because there doesn't seem to be a definite answer. Ive read quite a few threads about broken chains but none that ever had a concise answer to what happens inside the CC. They usually end in the person getting a new engine or car, rather than trying to repair.
Id like to know for sure as well because there doesn't seem to be a definite answer. Ive read quite a few threads about broken chains but none that ever had a concise answer to what happens inside the CC. They usually end in the person getting a new engine or car, rather than trying to repair.
cammerfe
Dedicated LVC Member
I'll pursue the answer to this question by calling my contact during the first part of next week. Answer then!
KS
KS
Spedley
New LVC Member
What exactly do you mean free rolling? Able to spin easily without a wrench? With 10.5:1 CR, its gonna be a tough turn with anything. Shouldn't any engine be able to turn over with a socket and bar on the front crank bolt?
Snowseeker
Well-Known LVC Member
This is the kind of stuff that happens in interference motors when belts/chains break:
97stscaddy
Dedicated LVC Member
I know how the innerds of an engine fare in the event of a broken timing chain. That doesn't answer the question which is, Is the 3.9L v8 engine used in the LS an interference design or non-interference design. We're looking for info on this engine specifically.
That last pic is impressive though. Most of the time you get one or two valves, but I've never seen someone get all of them.
That last pic is impressive though. Most of the time you get one or two valves, but I've never seen someone get all of them.
Snowseeker
Well-Known LVC Member
I would pretty much guaranty with the compression these motors have that they are interference motors.
Interested to find out for sure though.
Interested to find out for sure though.
mharrison
Dedicated LVC Member
:I I would be really surprised to hear that they are not interference engines given the high compression.
conclusion
okay, after reading hours of threads with this concern, here is what I have come up with. (1) this is not an interference engine or (2) This may be an interference engine, but only for the valves on the primary chain. There are just too many people braking the secondary chain with no engine damage. I heard a few people say it may be luck. There is no luck to it, either the metal hits or it doesnt, it only takes one split second. My conclusion based on these threads and my findings is that number 2 is correct. Let me know your thoughts....
okay, after reading hours of threads with this concern, here is what I have come up with. (1) this is not an interference engine or (2) This may be an interference engine, but only for the valves on the primary chain. There are just too many people braking the secondary chain with no engine damage. I heard a few people say it may be luck. There is no luck to it, either the metal hits or it doesnt, it only takes one split second. My conclusion based on these threads and my findings is that number 2 is correct. Let me know your thoughts....