1. Crankshaft Gear (21 teeth) 2. Camshaft Gear (42 teeth), and 3. Oil Nozzle to keep the interface of the two gears well lubricated.
Timing Gear Notes
Jan 2018-2023, R. Kwas, Updates on-going (Comments and Additional material added.)
Failing Timing Gear Noises
Confirming a Failed Timing Gear
Replacement Timing Gear Options
Loose Timing Gear Nut
Notes and Experience on Timing Gear Replacement
-----------------------------------------------------
The Camshaft, operating the Valves, and Crankshaft, to which the Pistons are connected, are connected by Timing Gears. These gears have an exact tooth-count relationship of 2:1, which keeps the correct, and precise Crankshaft to Cam turning and timing relationship necessary for the 4-Stroke engine. Oil-Pump and (mechanical) Fuel-Pump as well as Distributor also are operated off the Cam, and they benefit from turning half as fast as the Crankshaft.
1. Crankshaft Gear (21 teeth) 2. Camshaft Gear (42 teeth), and 3. Oil Nozzle to keep the interface
of the two gears well lubricated.
The B18/20 Volvo engines have been said to be "bulletproof", and there is much truth to this...they seem to love running at elevated revs for hours on end...even when very low on oil (see: Link). If Volvo B18/20 engines have any weakness, it would have to be the Timing Gear failure after high mileage. From the factory, Crankshaft Gear is of Steel, while Camshaft Gear is of a fiber reinforced phenolic on a steel hub construction. The original equipment phenolic gear was supplied to Volvo by SWAG of Germany (not Scientific Wild-Ass-Guess, but SüWest Aktien Gesellshaft). The reason for the phenolic construction is to reduce the noise factor, but these Gears seem to have a limited service life. It has been suggested that the limiting factor is mileage, but as Irv Gordon's experience does not show this, the author is convinced, gear failure is more a function of the number of thermal cycles.
The typical failure mode is that the steel hub separates from the phenolic, and this is more consistent with cumulative stress from thermal cycling. (See also: My Explanation of Fiber Timing Gear Failure.) Thankfully, this actual failure usually occurs slowly, and when actual separation occurs, it is not complete and catastrophic, resulting in a dead engine, but allowing one to limp home with a running engine, albeit with "unique" engine noises. Stories abound of drivers who got significant, even lots, of miles on the engine after it started making these noises...probably not on the highway, but it does suggest a pretty good degree of failure tolerance... If the TG ever looses drive completely, the engine will obviously be incapable of running, but thanks to the fact that B18/20 are not "Interference Motors" (where Valves occupy the same space Pistons occupy, separated only by Crankshaft to Camshaft timing) (Reference: https://en.wikipedia.org/wiki/Interference_engine ) no catastrophic damage to engine results.
A Timing Gear, showing the typical failure mode...outer teeth which interface with the Crankshaft gear are intact, but metal center hub has separated from the phenolic outer section:
Detail of a failed TG...showing interface teeth on hub and teeth on fiber
part can remain engaged enough to provide Cam drive for a while, even after they are
no longer intimately bonded (the Timing Cover is near enough to keep the Hub and
Gear engaged sufficiently to function, for a while). This explains why
engines can keep running, sometimes for quite a while...but the separation does
make itself known by the noises engine makes...as a matter of fact, in the
opinion of the author, it is the contact with the nearby Timing Cover which
actually makes those "unique" sounds.).
Failure of Timing Gear:
Video by Derek of the British Volvo Owners Club Forum:
https://www.youtube.com/watch?v=nGykPiE43Ik
-----------------------------------------------------
Replacing Timing Gear
Although I have heard several failed TGs first-hand (even one shortly after first-start of a new engine, although it turned out not to be the typical failure mode. See: Loose Timing Gear Nut below!), I have never actually had a TG fail while in service while driving...I typically replace the fiber gears preemptively with original equipment fiber gears during engine rebuilding time. The one on Wendy's 1800 did decide to fail one time, but as luck would have it, while I was away, out of the area, so Bob G. (probably one of the few guys I would ever trust to work on one of my engines) stepped up and came to the rescue...Timing is Everything (pun intended!)...so I could not include my own record of an in-service failure and replacement here, but I have included a link to a thread with some good practical notes of such a recent occurrence, which was well documented on the British Volvo Owner's Club forum, including with Youtube videos.
Thread Timing Gear Replacement: http://www.volvoforums.org.uk/showthread.php?t=250654&highlight=Timing+gear
My remarks to that thread (comments and additional, not part of the original posting added):
"
They do usually manage to get us home even when they're hurt, don't they...
I presume you've confirmed TGear failure by observing DistRotor free-play while
turning Crankshaft back and forth...more than about 10Deg of free-play pretty
much confirms TGHub is separating from Gear, and
it needs replacement. (...that is
obviously a Static Test. Alternately,
the Dynamic Test is checking the Timing of a running
engine with a Timing Light...it will likely show unusually high Timing variations
at steady RPMs, or ignition Timing
not returning to the same point after blipping the Throttle.
See also below!)
For TG replacement, Engine does not have to be removed...I wouldn't for
sure...that unnecessarily increases the scope of the job!...but Radiator should
definitely be removed to gain good working access...I would also raise the nose
of vehicle 6-10inches for access from below...Reminder: Two bolts secure Oil Pan
to TCover...but you knew that...
Gasket survival on disassembly depends on what type of sealant was used to
install last time...some types allow careful splitting away from the cover with
a razor/gasket knife...but success is pretty rare...so just in case you waste
Oil Pan gasket (which is likely), when you order TGear set*, I'd include an
engine gasket set, to use as patterns for reproducing (damaged part of) Oil Pan
and TCover gaskets, and use those...save the proper kit for later...trick to get
a a successful repair without leaks is to clean gasket area well of oil film
(with carb cleaner type solvent on a rag, multiple times, obviously minimizing
gasket remnants and solvent in crankcase) and when absolutely clean and free of
oil film, to use a tenacious gasket compound like Permatek 4H on reassembly.
* Beware...in recent times, there have been incidences of problems with some
TGear sets...fitting issues and noisy...I don't have specifics on which type
have these problems...I believe Alu, but hopefully others with first-hand
experience can chime in here!
If TCover does not presently have a modern Rubber Seal, now is the time to
upgrade! Also check WaPu for shaft-slop and replace now while access is best...
Take special care(!) after removing Nut from Cam (36mm / 1-7/16") not to push Cam toward
back of engine excessively...that can push freezeplug out at opposite end...and
that will require an engine removal for access to correct! Beware! "
-----------------------------------------------------
My Explanation of Fiber Timing Gear Failure
...Mileage vs. Accumulated Thermal Cycles [info not part of original posting added]
My post to a Facebook discussion of Timing Gears as related to Irv Gordon's frequent oil changes and high mileage:
" I think fiber gear life is less a function of oil change interval or mileage, instead, the way Irv drives (looong stretches at a time)...I think this goes a long way IMO to explaining why he gets lots of miles from a fiber gear and we driving mortals only get a few hundred kmiles. Since the typical failure mode of the fiber Cam gear is separation of steel hub from fiber part, I believe it is not so much a function of mileage, but more a function of number of engine temperature cycles. Fact is that the effects of the differences in coefficient of expansion at the bond of these two different materials will be cumulative as a function of number of thermal cycles...and that effect will be micro-cracks...the more cycles, the sooner the micro-cracks unite into bigger cracks to cause complete bond failure [or cause delamination at the phenolic to metal interface, allowing ingress of oil leading eventually to complete separation] (I've done life-tests on this very thing in the aerospace industry where we test for these kind of things, among others)...so gear can fail for some owners (who drive more typically, an average of short trips), at 100kmiles, and for Irv at ten times that...or maybe never, because of the types of extended trips he takes, but with less temp cycles...that's my explanation. "
-------------------------------
Replacement Timing Gear Options (non-factory fiber gear):
Aftermarket Aluminum/Steel Gears:
Manuf. Cloyes #2032S
-----------------------------------------------------
Reference Information:
Typical noises from a Failing Timing Gear, (especially after about the 28-30Sec mark):
Video by Derek:
https://www.youtube.com/watch?v=iXxSRQ0johk&feature=youtu.be
Confirming a Failed Timing Gear: If an engine is making those sort of noises and a Failing Timing Gear is suspected, two tests can/should be performed to confirm fiber gear failure, before actually removing Timing Cover, and undertaking serious internal work.
1. Dynamic Test, (Engine Running): Consistency of Ignition Timing should be checked with a Timing Light. If timing varies more than just a few degrees, and particularly that it does not return after a quick blip of the throttle, that certainly is consistent with a disconnected hub.
2. Static Test (Engine not Running): With Distributor Cap removed, monitor the Rotor position while turning Crankshaft manually back and forth...more than 10 Crankshaft degrees of lost motion is also consistent with hub acting like it is disconnected from fiber part.
------------------------------------------------------
Picture of O.E. SWAG Timing Gear set from an ebay offering.
-----------------
Tightening Torque for Cam Nut: Maximum torque of 80nm (59ft/lbs)
Ref: https://www.volvoforums.org.uk/showthread.php?t=250654&page=2 See Posting #17
-----------------
Steel Gears are available (these were OE on the 6 Cylinder motors), as are aluminum ones. A steel TG can be installed on the original Crankshaft gear, but aluminum gears must be installed in pairs as I understand the toothpitch (and maybe even count) are different from the OE gearset (Need to Confirm and add details.):
Steel Timing Gear set installed. Note no oiler is present at oil gallery (Yellow)!
------------------------------------------------------
Notes and Experience on Timing Gear Replacement:
Removing Timing Gear (or Remaining Hub) :
The typical Rag-between-Crank-and-Camgears-to-softly-bind-them-up-and-prevent-rotation-Trick, works well for removal and replacement of an in-tact TG...but if TG Hub has separated totally, first remove phenolic part of Gear, then hold counter-torque on Hub with a beefy slip-joint pliers as loosening torque is applied to Nut (36mm / 1-7/16") to remove. Using impact is very much frowned upon during tightening the Camnut, but limited impact ("soft-hammer") may be used for loosening!
This acceptable technique for loosening the Camnut with low risk for breaking the Cam is simply holding the TG Hub unceremoniously with the biggest pair of slip-joint pliers available (also: Botchlocks, for how they are often used to "Botch things up"... but in this case, it's not really possible to botch up the TG Hub!), is best done by a two-man team, with one holding the Botchlocks for countertorque, and the other applying loosening force on the wrench (36mm / 1-7/16"). If this is unsuccessful, limited impact loosening torque can be applied to the wrench, and this should result in the desired release of the Camnut. TG Hub should then simply slip off the Camnose. If a threadlocker is known to have been used, heat will be necessary to defeat it before applying loosening torque.
(IMPORTANT: DO NOT push Cam rearwards into the engine in the process of working on its threaded nose!...because it is quite easy to pop the Freeze-plug at the opposite end of Cam, and that would increase the scope of the job tremendously...and unnecessarily, especially if engine is still in-place in a vehicle, as it would require a total engine removal for access to correct!!)
Approved technique for removing Camnut and Timing Gear Hub after complete
separation.
Chris Thomas picture used with his kind permission.
My answer to a 
Amazon Forum posting asking for advice on removal:
"Channel locks pliers holding the Timing Gear Hub is what I'd also try! And only moderate loosening impact on the wrench (with a rubber mallet). ...a two man operation...one holding Channel Locks, the other (You!) on wrench...Good Luck!
Edit: In the process of trying to remove Timing Gear Hub, after removal of TG Hub it is CRITICALLY IMPORTANT TO REMEMBER not to push Cam rearwards into engine, or allow this to inadvertently happen! This can and will easily push the Freezeplug at rear of Cam out of place, increasing the scope of the work tremendously (and unnecessarily, if this is simply an engine-in-place TG replacement!...I can see engine is out and on a stand so this is not, but Caution still applies!) Cheers"
"Installation:
The Retaining Plate in combination with Thrust Ring, set the Camshaft End Play. This is a repost of a pretty important IPD notice on the subject.
Also...NEVER use an impact driver to tighten Cam Nut of a replacement Cam. It's OK to use it only on a Cam which is being removed and retired from service, but subjecting a new Cam, which is a machined casting...certainly NOT intended to, or capable of, withstanding those kind of impact forces, to such impacts, risks breaking off front of the Cam!
There is a time and place to use your groovy new impact driver...when installing a Camshaft is not one of them!
Loose Timing Gear Nut A properly torqued Camnut is clearly pretty important! The author has seen first-hand an insufficiently torqued Camnut loosen within 5 minutes of initial Start-up of a newly built engine, (Steel TG on an engine intended for turbocharged service). This resulted in those terrible noises again, this time, from Camnut striking the Camcover. After removal of the Timing Gear Cover, and seeing this was the cause, the Camnut was subsequently safety drilled, properly torqued, and finally safety wired to prevent reoccurrence.
Reference: Torque Tech Article
------------------------------------------------------
PLACEHOLDER FOR TIMING-COVER (REAR CRANK) SEAL UPGRADES FROM FELT RING TO SPRING LOADED NEOPRENE
------------------------------------------------------
PLACEHOLDER FOR VALVE ADJUSTMENT -------- IS THIS A GOOD PLACE FOR THIS???
------------------------------------------------------
Links:
http://forums.swedespeed.com/showthread.php?231377-Timing-Gears
http://forums.swedespeed.com/showthread.php?166459-Changing-out-cam-in-1974-144/page2&styleid=14
http://forums.tbforums.com/showthread.php?t=194582
------------------------------------------------------
Finally...if your Timing Gear fails like this one, and sheds half of it gear-teeth, you will not be able to "limp home".
Catastrophic Timing Gear Failure. F. Floccari picture used with his kind
permission:
Another failure mode of the TG...hub has not separated, but a number of teeth have been chewed from gear. This would clearly result in an immediate motor stoppage accompanied by some gut-dropping-into-bowels-noises (!) with zero chance of restarting, but thankfully, no piston/valvetrain damage will occur as the B18/20 motors are not "interference" types.
------------------------------------------------------
External material sources are attributed. Otherwise, this article is Copyright © 2018-2023. Ronald Kwas. The terms Volvo, IPD, SWAG, Cloyes are used for reference only. I have no affiliation with any of these companies other than to try to keep their products working for me, help other enthusiasts do the same, and also present my highly opinionated results of the use of their products here. The information presented comes from my own experience and carefully considered opinion, and can be used (or not!), or ridiculed and laughed at, or worshipped, at the readers discretion. As with any recipe, your results may vary, and you are, and will always be, in charge of your own knuckles, and future!
You are welcome to use the information here in good health, and for your own non-commercial purposes, but if you reprint or otherwise republish this article, you must give credit to the author or link back to the SwEm site as the source. If you don’t, you’re just a lazy, scum sucking plagiarist, and the Boston Globe wants you! As always, if you can supply corrections, or additional objective information or experience, I will always consider it, and consider working it into the next revision of this article...along with likely the unique metaphor and probably (likely) wise-a** comment.
