1GR-FE valves interfering with piston when timechain is off

I think the answer to this question is NO but I just want to confirm. If the timing chain is off, meaning no synchronization between the crank/piston position and cam/valves, is it possible under any conditions for valves to interfere with the piston (and possibly break) if you are spinning the camshafts manually with a ratchet? The reason I think it is NO is because the depression in the piston top surface is made to clear the way for valve range of motion to avoid interference.

The reason I am a little skeptical is because I can recall different people saying different things about the interference status of 1GR-FE.

 

1GR is an interference motor. Valve reliefs in the piston are for clearance under normal operation when valves are partially open with the piston at or near TDC

 

does that imply it's not safe to turn camshafts when the timing chain is off?

 

I definitely would not be spinning the cams out of timing from the motor forcibly.

 

For sure. If I have to do it, for testing, I will make sure none of the pistons are in TDC, I have a rod I stick in for that.

 

What are your sources for that info?

I have researched this before and there are several posts & threads on here and the greater internet saying the 1GR-FE is non-interference.

Edit: I have no first hand experience with this and would love to find out for 100% sure. But Im not going to tear mine apart just for that haha

 

I was thinking something along the same lines -- because both the valve domes (or whatever you call it) on the head side as well as the piston top depression are concave, which SEEMS to offer plenty clearance for the valve range of motion (again, SEEMS).

does anyone know what that range actually is? I would guess not (much) more than 1/4". I'm curious to find out more precisely.

 

Have the timing set properly, all points lined up, before removing the cam shafts. Then you can rotate carefully.

Timing chain engines are typically interference engines. This is why it has a chain. Non-interference can have belts.

There have been over-rev issues with these engines, where the pistons did hit the valves, but that is more a spring issue.

 

In my engine's current configuration, even with larger reliefs, it is definitely an interference engine. I have to be extremely careful rotating the crank, if the cam shafts are still in, without the chains

 

There are actually 2 types of interference motors, on were the piston hits the valve, and the other were the intake and exhaust valves can interfere with each other. Not sure what this engine is, but most modern engines are interference motors. Most pistons have relief cutouts, and most are not deep enough for a fully open valve at TDC, they are only deep enough to fit the valve when it opens before and after the piston has moved to TDC, at the relevant points in the intake/exhaust strokes. I don't know why you want to move the valve train independently of the crank but its not a good idea. Only move them as necessary to set up the timing.

 

So you’re saying the possibility of valve float is real, huh

I know a guy that might have gotten really, really lucky on a 3-4 miss shift.
If you’ve never heard a Honda 1.6L engine bury the tack at/over 9K rpm, it’s definitely a sound you’ll never forget.

How I managed to NOT do any damage is beyond me. Maybe because the engine was fairly new.
Or maybe the man above was looking out for a dumbass kid. Either way, I got lucky.

 

When removing a motor it’s common practice for me and other I work with to put it at tdc. Cylinder 1 all the way at the top. And when you need to spin the cams before you do turn the crank 45 degrees. That way no piston is all the way at the top. Never will hurt anything.

 

That's what I was saying earlier

 

I yank out cams at any position, it closes the valves and when I re-set them in, I do 1/4 turn before TDC #1 so the pistons are down a hair.

I treat all chain engines like interference.

If you're worried about rotating the cams, set the crank back before tdc, then spin the cams as needed.

 

So you’re turning the engine over slowly with a ratchet, with the timing chain off, and it comes to a stop. Whacha gonna do? Call Ghostbusters? Give it all you got? Or stop? Yeah, that last one might be the best option. If you’re not totally ham-fisted with that ratchet, no damage will be done even if there’s contact.

But I still have to question WHY in the first place. What is your goal here?

 

god this is great lmao

 

Another foampile fuckery thread lol

 

you're essentially saying that "is this an interference engine?" is a "fuckery" question -- because you don't know an answer.

evidently it's a good question because there is no consensus. there is no conclusive answer to the question posed in the OP. no one has said, with certainty yes or no whether a piston fixed in the TDC position would damage valves if they were working without syncro with the crank. that's because you're lazy to contemplate scenarios.

it is standard rhetoric of a hater to derogate a question which they can't answer by irrelevant retorts such as "why do you want to know?" (the answer to which is "just because")

 

there could be many reasons to want to turn camshafts with the timing chain still off. for one, to see that the cams have been installed correctly as soon as they have been installed -- because in general engineering, defects/mistakes are easier to fix as soon as they are made than waiting until later and more things are built on top of the mistake.

I am surprised I have to explain this common scenario to people who should be technically inclined.

 

I was always told there are no stupid questions but there are inquisitive idiots. You’re like a 3 year old trying to rebuild an engine asking why the sky is blue. Read the manual, assemble engine, move on.