1999-2009 [Subscribe to Daily Digest] |
The steel does not stretch*, the issue is wear. So a stretched chain is a lubrication issue. With the now essentialy mandated Mobil 1 0W40, and changes to suit driving profile, I do not think that such 'stretching' will occur. To suggest that the TC needs to be routinely replaced at 100K is absolutely bogus. So that is the good news. (High amounts of chain wear can also be expected to be accompanied by large amounts sprocket wear. The balance chains will suffer the same fate, and experiece tells us that the balance chains are typically the first to show sings of failing.)
* yes a motorcycle drive chain can stretch, especially when new. But that application is subject to shock loads and other abuse. The timing chain application does not see any loads of this nature that would cause the metal to deform. Motorcycle drive chain stretch is noticeable when one abuses a new chain and a shock load stretches one half of the chain, then the drive is noticeably uneven and bogus as the chain pitch has changed in one half of the chain.
A 'stretched chain' means that there is abnormal metal wear. So cylinder walls would also be effected. Wear metals themselves accelerate wear as they are hard and most of these particles are so small, that they pass though any full flow oil filter. These have little effect on things like journal bearings, but things like chains(2), sprockets(6), rings/cylinders/pistons, valve guides(16), cams lobes and followers(16) are all boundary layer lubrication where the fluid films are very thin and hard wear metal particles do create more wear;so these are sources of wear metals as well. The only way to remove the wear metals is by draining the oil, or bypass fitlers, or very strong magnetic drain plugs or such that will remove (only) the iron and steel wear particles. When an engine has high wear metal contamination, a fair amount of this will drag over from one change to the next. Running the engine on the street prior to the oil change is probably better at stirring up such stuff prior to the draining VS backing out of the garage and idling for a few minutes. An amount of oil never drains from the engine, and the oil cooler and hoses do not drain during a change.
And finely divided metals act as polymerization catalyists that further break down the oil and produce plastic/aka-sludge. In combination with moisture (which creates acid), ethanol and other fuel additives and the soup of blowby gasses that include all kinds of partially burnt and reactive combustion products, there can be all kinds of unwanted chemical reactions going on.
So early chain stretch/wear is not normal.
Badly fouled injectors that spray fuel onto cylinder walls can massively increase wear at those locations and begin a cascade of wear metal induced wear. (Stuck piston rings allow for large amounts of blowby gases, moisture and fuel contamination and accelerated piston/cylinder wear.)
Chemical breakdown of the oil induced by fuel contamination (stuck rings), moisture(short trips) and whatever else contributes to oil sludging is a significant issue.
An oil that cannot stay fluid on the top compression ring grooves will lead to stuck rings. Only a good and real synthetic oil will resist this long term. Stories of old C900s that ran forever on dyno oil do not apply, as the compression rings are not much closer to the piston crowns which increase the temperatures greatly. Not much oil gets into the rings and the lubrication circulation can be considered almost zero. The rings were moved up to reduce the volume of gases in the piston clearance above the rings. The fuel/air in this thin annular cavity does not combust very well at all. With high compression and turbo boost, the amount of A/F in that space is more that one would think at first. So that change was done to reduce hydrocarbon emmissions.
It might be that when synthetic oils do break down, that the reactions produce results that are in some ways more nasty than dyno oil. But we don't know about such pathological details of oil failure. You can use the Mobil 1 0W40 (or 5W40 for 2003-), and have an advantage. Stuck rings may release with the use of the right synthetic oils, but the good news is that stuck rings can often be released by solvent type additives or flushes. AutoRX is also effective, but not dirt cheap like the other items. Injectors can be easily cleaned with Techron Concentrate, which also cleans combustion chambers. And as well, one should expect that Techron will get to the rings on engines that have stuck rings and/or larger amounts of blowby gas problems.
As for catalytic oil polymerization, there are paints, stains and oil finishes where oil oxidizes and forms a hard plastic material as part of the dying or cure. One can purchase a product called 'Japan Dryer' that is solvent with metal compounds that act as calylists to greatly increased polymerization reaction rates. And these do contain lead which would surprise many in this day and age. Bearing wear releases silver, copper, tin, lead and perhaps some nickel and other things, piston rings release iron, nickel, chrome and other metals. So the analogy between wear metals in oil, and metals added to paints and such to make them polymerize; is very compelling!
, Thu, 3 Mar 2005 03:36:41
, Mon, 7 Mar 2005 18:54:39
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
