2.7L 2TR-FE Inference Engine?

Hey Guys,
I'm trying to determine if the 2.7L 2TR-FE engine in my 2005 Tacoma is an interference engine. Does anyone on here know?

 

Pretty sure it is. But because it has a timing chain you shouldnt have any issues.

Why the question?

 

I accidentally turned the crankshaft counterclockwise maybe a quarter turn. Trying to figure out if thats a bad thing.

 

did you have the cam chain off?

 

No. I was taking the crankshaft pulley off when this happened.

 

As long as the timing chain is on there is no harm. Turn it backward or forwards will not hurt it.

 

Great, thanks for the input guys!

 

For the record, it IS possible to do some harm. If you follow the timing chain path, it is designed to pull in one direction. Chain goes from cam on one side, down to an idler, up to other side, and down to crank. After the crank it goes back up and there you find a tensioner. All that tensioner does is keep the chain tight on the "slack side". If you turn backward, that tensioner can give and effectively lets the chain "stretch" and alter the valve timing. Unlikely you would hurt anything while loosening the damper, since you would probably feel the resistance should a piston contact one or more valves.

But it is advisable to use caution going backward because of the tensioner possibly compressing and shifting timing.

 

Sorry but that is incorrect. As long as the chain is in place and has not jumped the sprocket no harm can take place.

Here is some info;
http://www.4crawler.com/Photos/Misc/ToyotaEngines.txt

 

The question is, what do you do about the tensioner? I've worked on many a overhead cam motor, and have seen the tensioner give way when you pull the thing backward. To the point it is difficult to verify timing is correct without rotating the engine two complete turns in the normal direction to start the check over. The effect I personally watched was that when turning it backward, the cams don't turn smoothly. That slop in the timing chain as the tensioner compresses and allows slack to form allows the camshaft to turn in a jumpy way caused by valve spring compression and release.

I won't begin to speculate about the tensioner in the 4 cylinder engine. But in looking at the service manual, it is on the top of a long slipper, on the LHS of the motor. How strong it is I don't know. It might be stout enough that it can't compress. I've worked on some where I had to use a hydraulic press to compress the thing, then insert a steel pin to keep it compressed while re-installing it. But I have also worked on some that were not so stout. And they would compress with reverse rotation of the crank.

So whether it will happen here or not I certainly can't say not having had this specific motor opened up. But MANY motors can experience this issue. Most service manuals specifically advise against reverse rotation for this very reason, nothing else really minds going backward except for the timing chain / belt tensioner device.

If I was wrong in this instance, it certainly won't be the first time. But in the general case, there is certainly a risk associated with doing this. My assumption was that it _is_ an interference engine. If that is not the case, then of course there is no problem whether the timing chain compresses the tensioner, jumps one of the drive gears or anything else.

 

It is an interference engine.

 

The chance of skipping a chain by turning the engine backwards is extremely small unless the guides, chain and the tensioner are completely worn out and it probably would skip when you started the engine from cold because the tensioner would be slack any way.

 

Note I didn't suggest skipping a tooth although that is possible. But the tensioner can compress and that introduces slack when turning backward. Depending on where the engine was stopped before this happened, you might turn the crank enough to contact an open valve. Not saying it _would_ happen. But it is simply _possible_. I worked on a neon a few years ago where the engine could be turned backward and wreck the timing as the belt would definitely jump a tooth. I worked on a different neon and it took godzilla to compress the tensioner just to get the belt installed (I had to use a hydraulic press and insert a steel pin through a locking hole to hold the tensioner compressed so that it could be installed.) I suppose it depends on how paranoid the engineer was when weighing the option of how much tension to keep things tight, vs how much wear since more tension applies more pressure to the chain and bearings.

My answer was a more "generic" answer as opposed to one specifically directed at this specific motor since I have not worked on a 2.7 period. But knowing how they work, I would personally not attempt it just to stay on the ultra-safe side of the equation.

 

Ponder this. A 4 cylinder motor stops in one of two places every time it is turned off when the engine is rotated two of the pistons are going down two are at the bottom coming up no matter what way it is turned one cylinder has two valves slightly open all ready the other one both are closed. If the design was such when the engine stopped on compression the cam due to rotational force would continue to turn slightly putting slack in the chain/belt so if the interference was that critical it would run the risk of bent valves. There is enough slack designed into the system to account for the possibility other wise there would be plenty of bent valves. If one turns an engine and it is out of time they would have to turn it with a bar to do any damage or at least turn it pretty hard it would come to a halt as soon as a piston struck a valve. Now when you have an engine turning several hundred RPM the story changes rapidly when a belt or chain comes unguled.

 

I have a 2tr-fe, I parked nose up on a steep hill wresting it in 1st gear as the e brake has stretched, can this rotate the engine backward and cause damage?

 

No.

 

Thank you, could you please tell me more, such as if the car were to roll backward in first gear with the engine off, would that cause the same possible problems discussed above.

Sorry if it's a silly question

 

Because any slack in the chain is no where even close to being out of time.

 

OK so even if the engine does turn backward it will just take up the slack in the chain, anyway sees to be running fine, it never made any noise and is quiet on start up.

Thanks.

 

The problem is, while it is "taking up slack" the cam is not turning yet the crank is. Whether there is enough room there to let a valve contact a piston, and whether one would turn so energetically that a valve stem actually bends is unknown. However, many engines do contain warnings in the service manuals that explicitly state "do not rotate the crank backward"...

For me, better safe than sorry...