Timing gears

[sleek lemur]

Hi all,

Surprisingly, I couldn't find any conversations on this subject in forum history. My B18A rebuild will be fairly standard, but with K cam and 9.5:1 CR. What timing gears are recommended? Alloy would be tougher than fibre and cheaper than steel, so that's what I'm minded to use.

Unless anyone knows better.....

[Laird Scooby]

Originally Posted by sleek lemur

Hi all,

Surprisingly, I couldn't find any conversations on this subject in forum history. My B18A rebuild will be fairly standard, but with K cam and 9.5:1 CR. What timing gears are recommended? Alloy would be tougher than fibre and cheaper than steel, so that's what I'm minded to use.

Unless anyone knows better.....

Fibre would be the quietest and have the best "safety" out of the three, if anything goes horribly wrong and any valve to piston contact occurs or similar, it will strip the timing gear before trashing all the valves.

Steel is noisier but less chance of anything going skew-whiff on the timing and is more for competition use. I'm not sure where the alloy timing gear would fit in comparison to those as it all depends on the alloy in question.

You probably already know this though.....................

[john.wigley]

I have no experience of alloy, 'sleek lemur', but having once had a gear fail on my 'cooking' 145 many years ago, agree with 'L.S.' and would lean towards fitting steel.

Regards, John.

[sleek lemur]

Thank you LS and JW. That's a great help.

Steel is twice as expensive as fibre. Very interesting comment about the wheel stripping, rather than destroying the engine. Those clever old Swedes, eh?

Just need to work out where alloy fits in, buy am minded to go for fibre.

[c1800]

“ Fibre would be the quietest and have the best "safety" out of the three, if anything goes horribly wrong and any valve to piston contact occurs or similar, it will strip the timing gear before trashing all the valves.”

Dave, being a non-interference engine, how would this contact occur?

[Burdekin]

I have aluminium/steel ones from Tinus Tuning to go in.

[sleek lemur]

So is that steel or Alloy, Burdekin?

[john.wigley]

Originally Posted by c1800

“ Fibre would be the quietest and have the best "safety" out of the three, if anything goes horribly wrong and any valve to piston contact occurs or similar, it will strip the timing gear before trashing all the valves.”

Dave, being a non-interference engine, how would this contact occur?

I wondered about that as well, but would bow to 'L.S.'s near encyclopaedic knowledge of these cars. I can envisage a 'dropped' valve, but that would not necessarily be associated with a timing gear failure. Perhaps it is the increased C.R. that gives cause for concern, although didn't the B18B run 10:1 as standard?

As it happens, the gear on my 145, a B20A car (C.R. 8.7:1) did not disintegrate as such. The bond between the fibre gear and steel hub failed, which allowed the gear to spin freely on the hub and resulted in a 'failure to proceed'. I have no idea if this was a common failure in period, but the marginally higher noise seemed a small price to pay for the peace of mind provided by it's steel replacement.

Regards, John.

[old fart]

Hi Tim, I have an alloy timing gear from Amazon Cars on my 122s, after the original broke 7 years ago. On my first Amazon 30 years ago I fitted a steel set( they were cheaper then), and didn't find it noisy, although, as a lorry driver, I wasn't used to quiet vehicles. Regards, Andy.

[Laird Scooby]

Originally Posted by c1800

“ Fibre would be the quietest and have the best "safety" out of the three, if anything goes horribly wrong and any valve to piston contact occurs or similar, it will strip the timing gear before trashing all the valves.”

Dave, being a non-interference engine, how would this contact occur?

Pretty much as John suggested, chances are the CR has been raised but even without that, i've known pushrods bend for no apparent reason, tappets to stick in the block and so on. We also don't know what other mods are in there, high-ratio rocker arms for example.

In theory it shouldn't happen but as we all know, theories are made to be disproved!