peckinpah

Here is what mine looked like after 200k miles:





Since a couple of sprocket teeth are also broken, I gotta assume the tensioner was not doing its job and that chain was flailing around inside the case pretty badly.

So why was the tensioner not working? I'm thinking that it's because I had a habit of letting the oil level get quite low. This is because of a leak at the main engine seal that ends up being about a quart every 6-8 weeks. And so I would sometimes forget to check my oil for a few weeks at a time.

What say others about my theory of low oil level, causing loss of tension being at least one possible cause of guide breakage?

theAuthority

state your theory on how oil level affects the tensioner?

crafthorse

I think the plastic fails after so many heating and cooling cycles, along with an occasional tap from the chain and WHAMMY!

muddpigg

iTrader: (1)

I think its because people ignore the service intervals.

theAuthority

not everything lasts 200k miles without breaking?

peckinpah

So if my theory is correct, and people religiously keep their oil levels topped off, then the guides ought to last until the tensioner quits working on its own. And being such a simple device that's powered by oil pressure, the tensioner ought to in theory last almost indefinitely.

And also, once the chain is already flapping around in there, metal guides are eventually gonna break just like the plastic ones do. So the usefulness of metal guides is fairly limited, in that they merely prolong the inevitable for a few minutes longer.

I wonder if that's why Toyota engineers figured the plastic ones were good enough.

peckinpah

Sounds reasonable.

And if the oil level is really low, I would think that might interfere with the tensioner working properly even after the truck is running. Especially if combined with high RPM downshifts and stuff like that. Or that's how mind pictures these things breaking.

I think mine broke right during or after I unknowingly drove for 100 miles with a broken fan belt and my coolant boiled over several times.

theAuthority

http://www.accusump.com/

It's an electric oil pump. Will raise the oil pressure BEFORE you start your engine.

mcm375

The plastic guides become embrittled, it doesn't really matter what you do, eventually they will shatter. Get the metal guides w/ plastic/rubber coating and call it a day.

theAuthority

would still be nice to have that accusump unit to prevent scoring from cold starts.

might extend the life of engines a good percentage.

abecedarian

Here's the reality of why the guide(s) break:
Single row chains stretch more quickly than dual row chains. The tensioner receives pressure from the oil pump. This pressure extends the tensioner thus taking up the slack in the chain. Over time, when the chain has sufficiently stretched, the tensioner has extended as far as it can physically extend. Once this happens the slack in the chain, compounded by oscillations induced by the camshaft and valve train, can allow the chain to slap against the guide. Beat on a piece of plastic long enough and it breaks. Oiling the chain is not a significant contributor to its failure. Take a look at that hidden bolt in the front of the cylinder head for proof- it's hidden by a perpetually refilled puddle of oil, splashed up there by the timing chain.
The dual row chain Toyota used to use is also susceptible to stretching but since it essentially two chains side-by-side takes longer to stretch. The main downsides to a dual-row chain is its higher mass and increased friction which takes a tad more power from the engine to move.

The same principles apply to motorcycle chains too.

Matt16

Plastic gets brittle eventually in that environment. I think there is a lot of truth to what Abe is saying too.

Isn't the timing chain assembly supposed to be replaced every 100K?

Windsor

Accusump isn't an electric oil pump, it is a pressurized oil reservoir with an electric valve controlling collection or discharge.

The original intent was to keep the oil pressure up in certain V-8 engines under long high-G turns. It requires a handful of design shortfalls to cause this condition; low-profile oil pan (diminished capacity), week/insufficient drainback holes, etc. When a car took a high-speed sweeper at the track, there was potential for the oil to collect in the top of the "outside" cylinder head and in the lifter valley, eventually starving the entire engine.

Someone thought it would be novel to increase the oil capacity by adding a reservoir that could hold pressure and feed the system when the pump came up short. From there they added an electric valve (managed by switch in cockpit). This is the accusump system.

Later they figured out you could pre-pressurize your oil system by charging the reservoir while running and lock it down, and then pop the switch about a minute before you bumped the starter.

theAuthority

Yah I read that on the site. I called it electric, because it's activated electrically with valves.

I guess it could mean electric powered motor and pump system.

I think it is a good idea for both uses, high g's and pre-lubing.

Windsor

Meh, if you need it for high Gs, you need to fix yer engine.

For that purpose, it's band-aid tech.

theAuthority

also cheaper tech, also instead of a turbo timer it can be activated when a vehicle is shut off to shoot fresh oil through the turbo to cool it down naturally.

use it in conjunction with turbo timer?

Also it is an alternative to baffling a oil pan or using a dry-sump which is illegal in most forms of racing.

A lotus which is meant to compete in road races, during hill climbs suffers from oil surging/starvation.

TOYOTA 1

i agree with abe.

chain stretch + deep wear grooves in the tensioner + wear grooves in the guides = allot of slack. then the slack causes the chain to smack the brittle giudes and then they break.

also i think that in a low oil situation the rockers / cam would fail before the guides. and probably the crank and rods before them.

my thought process on being "low" on oil is, its different from being danger low and sucking air threw the sump. being a qt or so low on oil is not a big deal (unless its a race application or something similar). so i think being "low" on oil would not cause the guides to break.

and like gnarls would say, thats just my worthless opinion

theAuthority

email them and ask them that question. then get back to me

91Toyota

Yeah, every time I start my enigne (when cold) I can hear the valves clattering really fast for a second or so then it all stops. I'm assuming its building up oil pressure.

theAuthority

it does it when warm too, it just happens really fast.

If you could start your engine without hearing that clatter, would you?

My truck has been sitting for 4 weeks almost with no starts and I'm hesitant to go start it. I might drain a quart of oil out and pour it back in, than start it. Just to make me feel better.