techie - 4th gen interference engine

[tcpoob]

yes i searched the forum but have not found definitive answers ;-) so the questions are:

1. is the 4th gen v6 of non interference type? yeah i know it's chain so this is less worry.

2. is the 4th gen v8 of interference type? the Gates site pdf seems to indicate so as of 2004 model year of the V8.

3. i was under the impression non interference engine is a more modern design but i've been told it's the contary by my boss. he rebuilds antique cars as a hobby so he's probably right. he said olden days most US engines are NON interference but due to air emission/pollution etc, many Jap cars adopted interference engine design which made it popular. what do you guys think?

4. if interference engine is so potentially bad with regards to accidental repair when time belt/chain breaks, there must be a reason it's chosen in many Honda etc. why? is it the higher compression ratio, larger volume of air/fuel intake/exhaust, ... ?

Thanks.

 

[>MR2turbo4evr<]

Depends on the compression. My MR2 turbo has low compression and therefore is a non-interferance engine. Higher compression engines aren't......

 

[TeCKis300]

Modern high performance and high efficiency engines dictate the need for high compression. High compression typically requires little squelch space between the valve and piston hence most modern engines are interference designs.

Don't worry about the timing chain/belt. You bought a toyota. As long as you service the motor at the proper intervals...it's a non-issue. You're decision should be based on other priorities.

 

[Northof49]

Historically, very few Toyota's have had interference engines.....some of the diesel motors and 2 or 3 gas motors from the 80's/early 90's. Some newer V6's as well, but not sure all of which. AFAIK, the 4.7 V8 is not an interference motor. Most interference Toyota motors are timing-chain equipped.

Either way, interference engines are nothing to worry about. The only people that EVER have problems with them are those too stupid/cheap to do regular maintenence......it's not like the thing is going to blow at 1K past the interval, you gotta really push it to experience a failure.

If one follows such patterns and is too cheap to replace a t-belt, it's likely he/she will neglect other basic maintenence and have plenty of shit fail even on a timing chain equipped vehicle.

 

[grapes]

HURRAH- my first post after many technical problems, as stated above very few Toyota engines are interference engines and that's a good thing. My 1998 Subaru Forester broke it's timing belt at 31,000 mile DOHC interference engine, not a pretty site. Over 6k for new short block rebuild at Subaru dealership Under waranty). Next sad story 1995 Elantra GLS same thing timing belt at 49,000 interference engine, holed pistons bent valves you name it. Again new engine under warranty. I've had about 40 cars in my 53 years and these are the only 2 that broke belts or chains, and i am meticulous about car maintenance. So lets all cheer for non interference engines.

 

[Thai]

HURRAH- my first post after many technical problems,

Welcome to the forum...i am not sure why you slipped thru the cracks. Sorry for any inconvience.

 

[POS Racing]

Depends on the compression. My MR2 turbo has low compression and therefore is a non-interference engine. Higher compression engines aren't......

Wow...

If the valves can occupy the same space the piston can you have an interference engine. If the valves do not ever occupy the same space as the pistons you do not have non-interference engine.

This problems on interference engines is when you have a timing belt failure so the valves stop and the pistons hit the valves.

Interference Engine

Non Interference Engine

It would take a pretty good failure on an engine with a timing chain to kill a motor, now a neglected Honda with a belt is a different story. : Good information available here!

 

[greasefingers]

I have been looking at the cylinder heads, in my FSM, and even though it does not state if it is an interference engine or not; I would have to say guess YES. There are four values per cylinder and no where for them to hide in the cylinder. Also there is very little distance between the valve and the end of the head.

 

[MicaBlue03]

Interference vs. compression ratio

I suspect that interference is more complicated than compression ratio and 4 valves/cylinder. The V6 has 4 valves and a higher compression ratio than the V8 (or at least it did until the V8 got VVTi) and its reported not to be an interference engine.

It's probably also influenced by compression chamber shape, valve angle, valve lift, and other related stuff.

IMHO the best thing to do is to make sure you stay up with recommended maintenance and otherwise not sweat this issue. There are so many other things to discuss!

 

[greasefingers]

I have rebuilt three engines in my life-time. As long as my FSM diagrams are correct, the regular v8 (not the VVT-I) must be an interference engine.

The compression ratio, IMO, does not matter. The only thing that I can think of is the head space in the cylinder head.