Interferenc or Not

[BigDingus]

Hi all.

I had the misfortune of one of my small timing chains snap.

I'm now looking to fit a new chain plus other bits.

Before I start I'm wanting to find out it the engine in an IS250 is an interference engine or hopefully not.

I did see on Youtube a guy turning a camshaft but I like to bee 100% sure.

[ColinBarber]

I'm 99.9% sure it is an interference engine.

[Linas.P]

54 minutes ago, BigDingus said:

Hi all.

I had the misfortune of one of my small timing chains snap.

I'm now looking to fit a new chain plus other bits.

Before I start I'm wanting to find out it the engine in an IS250 is an interference engine or hopefully not.

I did see on Youtube a guy turning a camshaft but I like to bee 100% sure.

Do you mean an ACTUAL timing chain snapped? Or do you mean accessory belt snapped?

Because I have NEVER heard of chains snapping on these engines and frankly I don't believe it is possible (until I see one myself)... unless the engine already been catastrophically destroyed and chain snapped after rod exited the side of the engine. 

If later, then it is not an issue at all, it only drives accessories, water pump, A/C and alternator... it could snap because maybe one of them or tensioner locked-up. It is not ideal of course and the actual cause has to be determined (those belts can easily last 100k miles, so not exactly common to snap for them either)... and it is important to make sure engine was not overheated as result. Overheated 4GR-FSE (the engine in your car) are junk, they warp heads, blow head gaskets and generally are not repairable.

General rule of thumb - Toyota engines that have chain are interference engines, most of engines of VVTi (all?) are interference engines. I can't find reliable information of whenever 4GR is interference or not, but 2GR is and generally speaking most likely 4GR is interference engine. BUT that is moot point - your engine has to be messed-up in some fundamental way for it to snap the chain and it doesn't really matter whenever it is interference or not, after snapping chain it would be full of junk and not salvageable anyway. There are no circumstances where chain snaps and engine survives, although as I said you probably would be first person in the world to snap chain on 4GR so I assume you just snapped the accessory belt.

Now if you happened to need a new engine (which you 100% will need if you snapped the chain), then I can let you have one for cheap. Even just assuming it just needs chain replaced and there is certainly no other damage to the engine... it would still be cheaper to replace the whole engine, than to replace the chain.

[BigDingus]

Thanks for helping guys.

Ive now removed bank 2 exhaust camshaft.

Ive also checked all the valves and they are in perfect nick.

The only damage apart from the timing chain, are 2 cam followers, now removed and ordered, plus the chain tensioner.

I gingerly rotated the cam and there was no indication of any valve coming into contact with a piston.

Linas. The Lexus mechanics and the 2 storemen had never heard of the secondary timing chain snap. Just my luck.

Im hoping the chain can be split or fitting it will be a nightmare.

[Linas.P]

You certainly the first person to have achieved that... may be "luck" as you say.

Just please clarify, you said "secondary timing chain snap" - what do you mean? So it isn't your main chain that snapped, but the small chains that only drive VVTi (intake and exhaust valves)? i.e. as highlighted below?

Your engine is absolutelly, 100% not worth fixing (I must say - my biased opinion here). Not only it is uneconomical time wise, it is uneconomical literally. Let's think about just money, forget the time it will take.

You need new chain, new tensioners, all new seals, new secondary chains... not 2 new cam followers - all new cam followers (24 of them!). Are you imagining you replace 2 cam followers when the rest of them already has worn over the time and be done with it? Why would you invest in repairing the engine when you can't trust the rest of the cam gear? What about the rest of the engine? It needs full rebuilt isn't it? Chain snapped, then there will be debris in... everywhere... also it is not like something soft like sealant or bearing material, it is hardened steel, chains are hardened steel. So you need to split bottom end as well, inspect all the bearings, crankshaft and realistically when you there - replace all the bearings. Slip all engine apart and clean every single oil passage.

Only the gasket kit is £344 + VAT + delivery... and you will need it for sure. I just put absolute bare minimum basics here and you are close to £1000 just in parts to rebuild it. But how can you trust VVTi adjustors, camshafts etc. You need to inspect crankshaft also, you need to inspect piston pins for blockage... Like really, where do you realistically stop inspecting the engine? It was compromised by "foreign material" of hardened steel variety (actually it is kind of "native" just doesn't belong in oil), everything needs to be disassembled down to bare block, cleaned, inspected and reassembled. Even if you just do bare minimum and replace just the parts that broke, it still going to be something like £500 with labour... and what for? So that your bearings go in a 1000 miles, because either oil passage is blocked or there are contaminants on the bearing surface? 

I mean sure, it is my assessment (and I have conflict of interest because I have engine to sell, so I am transparent with my bias here) but this sort of thing is considered "catastrophic" for the engine. If this would be some sort of rare, expensive or unique engine... like 2UR (form IS-F), then sure, it may be worth the effort to rebuild, but 4GR?! Just for reference - mine would be £400 if you pick-up, or whatever extra it comes to deliver if you want it delivered and I can warranty it for a year, I know it came out of running car.

By any means get second opinion, but I can't imagine any engine builder advising you to replace only few parts and giving any sorts of warranty for you.

[BigDingus]

Thanks Linus.

Lots of info there. 
Labour is nil as I’m the engine builder. 
Sorry I said follower, I meant rocker. 
Followers are seriously expensive. 
All the parts come to £375 and that’s with some parts that really ain’t needed but better to have them incase.

It is the 4GR I have. 
The rest off the engine is in good condition. 
Although not 100% perfect test, but compressed air shows no bent valves.

 

[Linas.P]

375 + time + risk, somehow does not sound like economical decision, but I guess you can take the risk if you are the one building. The valves holding pressure would be really last of my worry. Still not sure how you planning on checking and ensuring that you don't have contamination in the engine? 

Either way, if you need the engine shortly you know who to message 🙂 

P.S. forgotten to say, chain snapping for me sounds like symptom not the problem itself. So if I were you, I would try to figure out why it snapped, not simply replace it and leave the cause unfixed. These chains DO NOT fail (what mileage is the car? Unless it is something like 300k miles... it should not happen), neither the timing chain nor smaller chains that run valves. In poorly serviced car tensioners could fail, that could lead into premature wear of the chain, which would lead into it stretching and you get "check engine" light long before an actual chain actually snaps. In short - there should be warning signs. If it just snapped one day without the sign, then there has to be something that caused it, it wasn't manufacturing defect, it could not have been just normal wear, it has to be something "unusual". Was the engine messed with before? Maybe chain was previously split by some person, for whom I will avoid making epithet? Something not properly installed? In short - this just can't be normal, look for the cause past the obvious part that is damaged here.

[BigDingus]

Linas.P again loads to answer.

The main chain was replaced about 10,000 miles ago. It had streched.

All the checks have been done and there's no indication to why this chain failed. No snags... Nothing.

Timing on the rest of the engine is perfect. All moving free and easy. Thankfully no valves damaged. Bore check shows no sign of piston or cylinder damage. Cam has no damage. No valves bent. No lack of oil marks.

Actually there was one piece that was damaged, and I was amazed, a collets. None of our mechanics have heard of a collet being damaged.

Channels etc will be cleaned through before total reassembly. Including removal and cleaning of the sump, which is a nighmare on the GR engine due to the front of the sump fouling.

I agree the something must have caused this, but extensive investigation hasn't shown anything. Hard to think something other than the cam jamming, but agian all valves etc are fine.

We will see when the start button is pressed. This will be a while as I ordered 1 rocker short.

[Linas.P]

Okey, but that just support my view, you had engine with stretched chain (likely just lack of basic maintenance), I would have scrapped the engine back then, because if chain gone, then the rest of the engine is likely not good (kind of depends what mileage etc. but generally chain replacement is more costly then new engine anyway)... and now 10k miles later you have chain problem again. That is my point!

Isn't that exactly what I am saying - you throwing good parts after bad, what makes you think it won't have another issue in 10k miles? Also I am puzzled by the statement that there is "no damage"... yes there shouldn't be, presumably your chain snapped, the engine stopped, minimal damage caused, BUT the engine is now contaminated and "decontaminating" it will be major piece of work... and if you leave even small spec of chain bits in the engine, it will snowball into more catastrophic damage. So that there is no damage yet is really irrelevant, because short of complete rebuild I just cannot see how you can be confident there will be no damage in next 10k miles... especially after already having issue on the engine 10k miles since last major failure. It is not a question of whenever you can make it run, it is a question "how long it will last after that" and "is the effort fixing it now is worth it, if it blows-up after another 10k"?

I mean sure you have benefit of working on the engine yourself, I don't know maybe it is your hobby or something (I am have same issue, working on the car with electrical issues where it would have been more economical just to scrap it), but in my opinion that engine is not worth the effort.

Also I am puzzled with replacement of only failed bits, on these modern engines the tolerances are tight... you can't just replace one part here and one part there, it will in itself cause issues, if you replace just one rocker with the rest already being worn then there inevitably going to be imbalance and valvetrain vibrations. Is that enough to cause the damage... eventually yes, how long it will take nobody knows... but in either case it is kind of the case of "faulty unit". I hate it when people nowadays don't fix anything and throw whole "unit" away, but sadly it needs to be said - sometimes that is most economical thing. 

And I am not saying "it can't be repaired", what I am saying "it can't be repaired piecemeal like that". If one part in valvetrain goes, the whole valvetrain needs replacement... but who is going to do that at £2000? And if you not doing it "right", then why bother? Why fix it in a way that will cause problems in near future?

[BigDingus]

Linas I would agree that chains usually only have an issue due to bad maintenance. Low or bad oil.

I can’t comment for before I purchased the car, but it's been better looked after then most cars since it arrived here.

I'm fortunate to have the use of a 10 bay garage whenever I want. 8 of which have hydraulic ramps.

You’re mostly correct about Lexus timing belts, but they are not immune to stretching. Usually around 100K.

The last one I did, it was found to be the tensioner ratchet that had failed. This caused the tensioner to retract too much and let the chain run loose (and stretch) until the oil pressure built up on the next start.

I’ve never been one for just replacing things. I ALWAYS repair first.

The decontaminating was extensive and time consuming. Every channel was checked, cleaned, flushed and even blown through.

Quote: I hate it when people nowadays don't fix anything and throw whole "unit" away, but sadly it needs to be said: Unquote.

Sadly the mechanics here can’t usually FIX things. As you said, it’s down to economics. Far cheaper to fit a part than repair the old one.

I’ve been all over the engine with my mic checking the tolerances. So far all are within spec.

[Linas.P]

Never suggested you were the one not to maintain it, always assumed you got used car which likely came with maintenance lapses. 

100k is very low for chain, around 200k for cars that are not well maintained is about where the chains starts to fail, for it to fail at just 100k there had to be significant issue.

Regarding tolerances... it is not so much about tolerances as much as the parts needs to be evenly worn... you can't put half valvetrain new and half worn out and expect it to work well together.