Subject: Re: V12 timing gears
Hi Charles,
Welcome to the Forum, Club and V12 ownership.
This spigot is the odd sort of part that club spares might have, possibly unidentified; so worth a call to Robin if you haven't already done so.
My car is the next later chassis number to yours, and I am in the process of getting it running again. I last drove it in 1983!
Mine had the original factory idler gear, which was in fact made of "Celeron", a similar material to Tufnol. The aluminium (or possibly duralumin) one you have discovered would have been a later replacement. Beware replacing with another metal one. As you state, the earlier engines had bronze idler gears. Those engines also had oil jet pipes spraying oil onto the gear teeth. If your engine is like mine, you will not have those. Presumably Lagonda felt that the additional oil spray was not necessary for a fibre gear. I had a new gear made up by Freedom Engineering. I can email you details if you would like more info.
I had only owned my car a month, and only driven 100 miles, when this gear stripped. This was back in 1976, and the London firm I took it to averred that it had stripped because of oil starvation. Many years later, I discovered that this starvation was because my engine was missing the vibration damper. Believe it or not, the damper is deliberately designed to also act as an oil thrower for these gears.
Your issue however appears to be more likely a restriction in the oil feed to this spigot. Unfortunately after 40 years I cannot recall the oil feed, but Lagonda favoured restricting oil flow by the size of drilling, so there is likely to be a pinhole type hole that you need to attend to.
Now. The Celeron gear had a steel centre, with a pair of bronze open top hat bearings riding on that spigot. When my gear stripped, I found those bearings were a fairly loose fit in the Celeron gear boss. Were the bushes intended to ba a tight press fit in the Celeron steel centre, or were they supposed to rotate separately? The gearmakers making the new gear were unable to advise either way, so I went with how I found it, and they made the bushes up to be a loose engineering fit to the spigot and the steel centre.
Wrong decision. The new fibre gear worked loose on its new steel centre. That firm kindly made up a new steel centre, this time with bronze bushes pressed into place. So...the bushes must rotate with the gear, not separately to it.
I have to say that I noted no tendency for the retaining nut to self loosen. My engine is perhaps unusual in that just about every bolt and stud is drilled for locking wire or split pin, so I can be pretty certain the central stud is drilled and the nut split-pinned. I did take a few photos of the engine dismantled at that time; if I can find them and have one relevant I'll scan and email it to you.
Do take care to clean out all oilways. The V12's oil filtration was weirdly basic given the advanced engine design. Hence there is an enhanced possibility of sludge having built up and blocking or partially blocking oil feeds.
As you're probably aware, originally, the duralumin rods bore directly on the crankshaft. In my case, Dodge racing bearing shells were fitted at a later date, and these appeared to have worked well.
Right, now I'm off to continue removing the nearside front wing. As you will doubtless have discovered already, there are few V12 jobs that are straighforward. This one is typical. Removal is easy...if it wasn't for the headlamp mounting bar. The wing design means that needs to be removed completely. As it sits between cut-outs in the radiator shell, it can't be lifted up...and it can't be moved back because the fan is in the way. So...the radiator and bonnet also need to be removed. Just as well I was thinking of removing those items anyway!
Laurence
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