# Academic / esoteric question on early Toyota timing belt engines **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** engines\ **Created:** [March 20, 2025, 12:41am UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545 "2025-03-20T00:41:28Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![jtsanders](https://avatars.discourse-cdn.com/v4/letter/j/c2a13f/32.png) [@jtsanders](https://community.cartalk.com/u/jtsanders)\ **Post date:** [March 20, 2025, 10:47pm UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/21 "2025-03-20T22:47:41Z")
The 3.5L wasn’t available until MY2007. CarFax shows MY2003 Siennas for as little as $3000 and MY2007 for as little as $5000. @WesternRoadtripper1 can decide if the extra $2000 is worth it to avoid a new timing belt, which might cost around $1000. If a new timing belt is needed or assumed needed on the 2003, that makes the difference much less. ---
**Author:** ![Rainflurry](https://avatars.discourse-cdn.com/v4/letter/r/cab0a1/32.png) [@Rainflurry](https://community.cartalk.com/u/Rainflurry)\ **Post date:** [March 20, 2025, 11:57pm UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/22 "2025-03-20T23:57:56Z")
> [@texases](#): > > Could someone explain why the VVTi would be any more likely to have interference? My understanding is that the valve timing is altered, not the total lift, so I don’t see why VVTi would turn a non-interference engine into an interference engine. It’s not the camshaft lift that will cause the issue, it’s the opening point of the intake valve and the closing point of the exhaust valve. Max lift for both intake and exhaust valves occur when the piston is well past (intake) or before (exhaust) TDC. The intake valve opens at +/- TDC and the exhaust valve closes at +/- TDC. If the VVT advances and opens the intake valve too soon or retards and closes the exhaust valve too late, relative to the non-interference engine, contact between the valves and pistons is possible. I don’t know the specs on the Toyota engines here but I’ve built a number of race engines where interference would occur with only a few degrees difference in cam timing. ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [March 21, 2025, 12:14am UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/23 "2025-03-21T00:14:36Z")
OK, I can understand how the valves might interfere with each other, but piston to valve is determined by lift, the timing doesn’t matter with a broken belt. The valve either hits or it doesn’t at max lift. ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [March 21, 2025, 2:00am UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/24 "2025-03-21T02:00:46Z")
If the camshaft lift specs, piston height-compression ratio, rocker arm ratio (if it has them), connecting rod length (same piston spec), cylinder block deck height etc etc are all the same as the non VVTi as w/VVTi, then they are either both interference or non interference engines… If the valve at full lift does not come in contact with the piston when rotated 360/720 degrees then it doesn’t matter what the duration is or when the valve opens or closes… Now, I did read where the VVTi had more duration @ 236/236 (intake/exhaust) than the non VVTi camshaft @228/228 (intake/exhaust), but can not find any lift specs for the non VVT vs the VVTi engines, but a lot of times (but not always) when you have more duration, you have more lift, so there’s that… ---
**Author:** ![WesternRoadtripper1](https://avatars.discourse-cdn.com/v4/letter/w/48db29/32.png) [@WesternRoadtripper1](https://community.cartalk.com/u/WesternRoadtripper1)\ **Post date:** [March 21, 2025, 5:31am UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/25 "2025-03-21T05:31:11Z")
> [@jtsanders](#): > > The 3.5L wasn’t available until MY2007. CarFax shows MY2003 Siennas for as little as $3000 and MY2007 for as little as $5000. @WesternRoadtripper1 can decide if the extra $2000 is worth it to avoid a new timing belt, which might cost around $1000. If a new timing belt is needed or assumed needed on the 2003, that makes the difference much less. Your logic makes good sense, except for this: From what I heard on “The Care Care Nut” Youtube channel (mentioned in another comment), in the first two years of the timing chain engine there were _numerous and varied problems._ “AMD” – the shop owner and former Toyota master diagnostic technician at a Toyota Lexus dealership, posted a [video](https://www.youtube.com/watch?v=OJkjE2-O3wo) with his list for **"Toyota’s BEST and Worst Engines.**" He states that the list is based on his own direct experience as a Toyota specialist. Watching some of his videos, you clearly see he has a heartfelt reverence for certain engines. **AMD’s list included the 2004-2006 Sienna engine. _Not_ the 3.5L 2007-2008 engine.** Thus my preference. See attached screenshot from the video. He also says, at 2:20 in the video, that the **VVTi is an interference engine.** ![TCCN best Toyota engines](https://global.discourse-cdn.com/cartalk/original/3X/6/0/60a00167ab44616dbb02a91c30f73a0ada17b55b.jpeg) ---
**Author:** ![WesternRoadtripper1](https://avatars.discourse-cdn.com/v4/letter/w/48db29/32.png) [@WesternRoadtripper1](https://community.cartalk.com/u/WesternRoadtripper1)\ **Post date:** [March 21, 2025, 5:38am UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/26 "2025-03-21T05:38:45Z")
@jtsanders > [@jtsanders](#): > > The 3.5L wasn’t available until MY2007. CarFax shows MY2003 Siennas for as little as $3000 and MY2007 for as little as $5000. @WesternRoadtripper1 can decide if the extra $2000 is worth it to avoid a new timing belt, which might cost around $1000. If a new timing belt is needed or assumed needed on the 2003, that makes the difference much less. Your logic makes good sense, except for this: From what I heard on “The Care Care Nut” Youtube channel (mentioned in another comment), in the first two years of the timing chain engine there were _numerous and varied problems._ “AMD” – the shop owner and former Toyota master diagnostic technician at a Toyota Lexus dealership, posted a [video](https://www.youtube.com/watch?v=OJkjE2-O3wo) with his list for **"Toyota’s BEST and Worst Engines.**" He states that the list is based on his own direct experience as a Toyota specialist. Watching some of his videos, you clearly see he has a heartfelt reverence for certain engines. **AMD’s list included the 2004-2006 Sienna engine. _Not_ the 3.5L 2007-2008 engine.** Thus my preference. See attached screenshot from the video. He also says, at 2:20 in the [video](https://www.youtube.com/watch?v=OJkjE2-O3wo), that the **VVTi is an interference engine.** ![TCCN best Toyota engines](https://global.discourse-cdn.com/cartalk/original/3X/6/0/60a00167ab44616dbb02a91c30f73a0ada17b55b.jpeg) ---
**Author:** ![WesternRoadtripper1](https://avatars.discourse-cdn.com/v4/letter/w/48db29/32.png) [@WesternRoadtripper1](https://community.cartalk.com/u/WesternRoadtripper1)\ **Post date:** [March 21, 2025, 5:59am UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/27 "2025-03-21T05:59:24Z")
Maybe it’s just that I have an old computer, but this website forum seems to be more and more clunky every time I log in. The proliferation of ads is part of it. But every time I post on a thread, I immediately see two versions of my post. One has my content in ordinary “black”, and on the other, the content is medium grey. Does that happen to everyone? And after I’ve been logged in and take a break for something else and come back, like now, my typing gets far ahead of words appearing on the screen, the input is VERY slow. The strangest one is that I had just posted a **reply to jtsanders** , then saw my reply directed to @davesmopar. Maybe it was my mistake, or not. Either way, my apologies to both. Puzzling… ---
**Author:** ![WesternRoadtripper1](https://avatars.discourse-cdn.com/v4/letter/w/48db29/32.png) [@WesternRoadtripper1](https://community.cartalk.com/u/WesternRoadtripper1)\ **Post date:** [March 21, 2025, 6:16am UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/28 "2025-03-21T06:16:43Z")
Later in the video, AMD lists Toyota’s worst engines. Here is the screen shot showing one group of engines to avoid: 1AR and 2AR. Note Sienna 2010-2020 on this set. ![TCCN some WORST engines](https://global.discourse-cdn.com/cartalk/original/3X/5/c/5c44ed046934c89614d9aa3d32f4474ba88e5bb9.png) ---
**Author:** ![jtsanders](https://avatars.discourse-cdn.com/v4/letter/j/c2a13f/32.png) [@jtsanders](https://community.cartalk.com/u/jtsanders)\ **Post date:** [March 21, 2025, 11:54am UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/29 "2025-03-21T11:54:06Z")
If the engine has lasted for almost 20 years, would the issues still apply this late in life? Many problems apply to some, but not all mechanical assemblies. If a high percentage exhibit the problem then not all do. From what I’ve seen in the past from CR, a 4% overall failure rate divides the less than average from the much less than average ratings. ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [March 21, 2025, 12:43pm UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/30 "2025-03-21T12:43:58Z")
> [@WesternRoadtripper1](#): > > Maybe it’s just that I have an old computer, but this website forum seems to be more and more clunky every time I log in. The proliferation of ads is part of it. But every time I post on a thread, I immediately see two versions of my post. One has my content in ordinary “black”, and on the other, the content is medium grey. Does that happen to everyone? > > And after I’ve been logged in and take a break for something else and come back, like now, my typing gets far ahead of words appearing on the screen, the input is VERY slow. Not since I started using Duck Duck Go, But this is the only site I use it for, so far I have not had one ad and no slowing of typing… ---
**Author:** ![FoDaddy](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/fodaddy/32/717_2.png) [@FoDaddy](https://community.cartalk.com/u/FoDaddy)\ **Post date:** [March 21, 2025, 12:49pm UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/31 "2025-03-21T12:49:22Z")
> [@WesternRoadtripper1](#): > > Later in the video, AMD lists Toyota’s worst engines. Here is the screen shot showing one group of engines to avoid: 1AR and 2AR. > > Note Sienna 2010-2020 on this set. Also note that the 1AR is the 2.7L I4, that is _very_ rare in the Sienna. It shouldn’t be confused with the much more reliable 3.5L GR, which is the engine you’ll encounter 95% of the time (in the years where both engines were available). ---
**Author:** ![Rainflurry](https://avatars.discourse-cdn.com/v4/letter/r/cab0a1/32.png) [@Rainflurry](https://community.cartalk.com/u/Rainflurry)\ **Post date:** [March 21, 2025, 5:47pm UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/32 "2025-03-21T17:47:02Z")
> [@texases](#): > > The valve either hits or it doesn’t at max lift. You’re right. I was in full-on race mode (all engines were interference engines where I worked) when typing that and lost sight of the question. ---
**Author:** ![TheWonderful90s](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thewonderful90s/32/29584_2.png) [@TheWonderful90s](https://community.cartalk.com/u/TheWonderful90s)\ **Post date:** [March 23, 2025, 5:21am UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/33 "2025-03-23T05:21:38Z")
I’m fairly sure that all gasoline Toyota engines that use a timing belt are non interference. The interference engines use a timing chain. edit: davesmopar’s response below is correct. There is an interference engine with a timing belt. Quote from the [toyotanation.com](http://toyotanation.com) froum: “The 3.3L 3MZ-FE engine is a rare example of a Toyota engine with timing belt that is an interference. In most cases, Toyota engines with belts are non-interference, but the 3MZ is a rare exception.” ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [March 23, 2025, 2:34pm UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/34 "2025-03-23T14:34:36Z")
> [@TheWonderful90s](#): > > I’m fairly sure that all gasoline Toyota engines that use a timing belt are non interference. The interference engines use a timing chain. You might want to do a little more research next time before posting… ### 2) Timing Belt Problems We’re moving onto yet another issue that really isn’t a true design flaw. However, the timing belt is an important standard maintenance item. **Toyota 3MZ-FE engines are interference engines.** This means there is some overlap in the area in which the pistons and valves travel. This isn’t a problem when the 3.3 V6 ignition timing is on par. > **[Toyota 3MZ-FE 3.3L V6 Engine - Specs, Reliability, Problems](https://8020automotive.com/toyota-3mz-fe-3-3l-v6-engine/)** > > Learn about the Toyota 3MZ-FE 3.3L V6 engine. Toyota 3MZ-FE engine specs, reliability, problems, & performance. Pretty sure that is a timing belt… ![image](https://global.discourse-cdn.com/cartalk/original/3X/0/1/01b4464c1f2fdeb13d91bffd88526c3b17c217df.jpeg) ---
**Author:** ![WesternRoadtripper1](https://avatars.discourse-cdn.com/v4/letter/w/48db29/32.png) [@WesternRoadtripper1](https://community.cartalk.com/u/WesternRoadtripper1)\ **Post date:** [March 23, 2025, 4:53pm UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/35 "2025-03-23T16:53:37Z")
> [@FoDaddy](#): > > Also note that the 1AR is the 2.7L I4, that is _very_ rare in the Sienna. It shouldn’t be confused with the much more reliable 3.5L GR, which is the engine you’ll encounter 95% of the time (in the years where both engines were available) Thanks @FoDaddy, good info. I’m surprised to know that a 2.7L engine would be used in a Sienna. Would that have helped Toyota lower its overall emissions from the entire Toyota line? Or was it a turbo engine that produced a lot more power than a naturally aspirated engine of that displacement? Or just a big mistake? ---
**Author:** ![WesternRoadtripper1](https://avatars.discourse-cdn.com/v4/letter/w/48db29/32.png) [@WesternRoadtripper1](https://community.cartalk.com/u/WesternRoadtripper1)\ **Post date:** [March 23, 2025, 6:16pm UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/36 "2025-03-23T18:16:43Z")
What’s your source? ---
**Author:** ![FoDaddy](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/fodaddy/32/717_2.png) [@FoDaddy](https://community.cartalk.com/u/FoDaddy)\ **Post date:** [March 23, 2025, 6:41pm UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/37 "2025-03-23T18:41:56Z")
No, it was a normally-aspirated inline four cylinder, albeit a larger displacement I4. It’s inclusion probably had something to do with CAFE numbers, though it was only rated for about 1 MPG more than the 3.5L V6. [Compare Side-by-Side](https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=30176&id=30175) It proved very unpopular and was only offered for two model years. In exchange for that 1 MPG increase, it gave up about 80 HP and about 60 lb/ft of torque. A fairly noticeable difference in a larger/heavier vehicle like the Sienna. ---
**Author:** ![WesternRoadtripper1](https://avatars.discourse-cdn.com/v4/letter/w/48db29/32.png) [@WesternRoadtripper1](https://community.cartalk.com/u/WesternRoadtripper1)\ **Post date:** [March 23, 2025, 7:14pm UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/38 "2025-03-23T19:14:28Z")
Thanks for the reply @FoDaddy. 80hp less in a minivan weight over 2 tons seems ridiculous. I can see why it flopped. ---
**Author:** ![WesternRoadtripper1](https://avatars.discourse-cdn.com/v4/letter/w/48db29/32.png) [@WesternRoadtripper1](https://community.cartalk.com/u/WesternRoadtripper1)\ **Post date:** [March 23, 2025, 7:16pm UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/39 "2025-03-23T19:16:57Z")
Thanks for this @davesmopar. Glad to get this confirmation. I’ll read the piece you attached. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [March 23, 2025, 9:21pm UTC](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545/40 "2025-03-23T21:21:52Z")
> [@WesternRoadtripper1](#): > > 80hp less in a minivan weight over 2 tons seems ridiculous. For some driving environments 187 horsepower is sufficient. The 3.0 L engine in your Sienna is rated at 194 HP. The 2011 - 2012 Sienna has a 6-speed automatic transmission, yours has a 4-speed auto. Consider how much easier it is to replace spark plugs on a four-cylinder engine. > [@WesternRoadtripper1](#): > > I can see why it flopped. It was a strategy to increase CAFE values, whether or not the goal was achieved is not known. [Previous page](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545.md?page=1) [Next page](https://community.cartalk.com/t/academic-esoteric-question-on-early-toyota-timing-belt-engines/199545.md?page=3)