An Extra Timing Belt Idler For the 12 Valve V6

[Duk]

This is 1 of those things that annoyed the piss out of me  .
Why anybody would design an engine with such little belt wrap is beyond me! Well, maybe when the V6 was designed there were only so many belt sizes available and they had to work with they could get. But still........

So I decided to do something about it and add a much needed extra idler and a mounting bracket.
Unfortunately I did stuff up the bracket a bit (silly things like not being able to refit the fuel pressure regulator and I got the shape wrong ), so there will probably be a MarkII at some point.
The belt is a T034, and is 142 teeth instead of the original's 134. The drivers side cam pulley has about 4-5 extra teeth of contact with is nearly 50% more belt wrap. The passenger side cam pulley also gets more wrap, but it already had more than 25% to begin with (about 50% wrap now).
The idler is for the Nissan RB twin cam engines and is currently mount back to front with some washers being used as spacers. I'm on leave at the moment, so I don't have any access to lathes or mills to do any machining work, so it'll have to do for the time being.

Incidentally, I've been around quite a few belt driven camshaft engines and I have never seen any other engine with less than 25% belt wrap for a cam sprocket.

[david sammartino]

Nice work, and good thinking, but not to take anything away from you, however i just gotta ask, you mustve broken a few belts in the past to go to that sort of effort?
Ive personally done alot of miles in these v6's, and have run them in all states of tunes, from turbo, to standard road car, to modified n/a revving to nearly 8000rpm and never had any trouble, but i do change the belts religiously when needed and always check/replace things such as tensioners/bearings or oil pulleys if i even see the remotest issue, as im sure you can ask any 164 owner out there who has been a little "tight" in these areas lol and broken a belt.
If nothing else im sure youd have no problems running a thicker oil on start up now, and not jumping a tooth. Benefits i guess.

[Duk]

Nice work, and good thinking, but not to take anything away from you, however i just gotta ask, you mustve broken a few belts in the past to go to that sort of effort?

Actually I've never had an issue. But then I haven't done many K's with my Alfa. I was prompted to do it based purely on the above mentioned lack of belt wrap and number of horror stories I've read about skipping belt teeth.

I have never heard or read of any other engine suffering from timing belt related problems like the 12 valve V6's. I'm a firm believer in correct maintenance, but I still call it bad engineering. The worlds most elaborate belt tensioner (which obviously requires periodic maintenance) and the worlds poorest cam sprocket wrap........... Hmmmmmmmmmmm 

If you look at the trouble Alfa went to with the 24 valve engines to improve belt wrap. Each camshaft sprocket has 25% or more wrap. And they also use the radius tooth profile, a profile which is much less prone to climbing out of it's 'groove', then they must have felt it was needed.

[david sammartino]

I guess with alfas we always hear alot of "stories" sometimes, and im sure someones cousins uncles grandfather may have indeed encountered an issue at some stage.
When it comes down to it, im sure it is always better to be safe than sorry. If you have the time than why not.

In regards to the newer v6's, im sure it was more a matter of it being a completely different head setup being quad cam and thus needing a completely different belt setup, (no cam belt driven oil pump) and the type Of belt available at the time of design, but at the end of the day, belt tooth design or not, 3 years or more then 60k can kill either setup, and whilst in the 24Jv it may be the actual belt or idler being the culprit, in the 12v it may be the oil pump pulley or tensioner etc, i can only reinforce what i said earlier in that with proper and on time maintanence, you can almost guarantee being trouble free. This is however from my experience only though and i will admit that i run a blocked tensioner on my 12v and am very fussy bout belt changes on my gta.

[Duk]

The 164 24 valve engines still used the auxiliary input driven oil pump.

Most (probably all) of Toyota's over head cam V-engines use only 1 pulley per bank (4 cam engines but with gear driven exhaust cams). From what I've seen, they always use an idler between their cam sprockets plus 1 on the return side of the engine, and get 180*/50% or slightly more belt wrap. They also have much longer belt change intervals, think 100,000km minimum. My guess is that they rely on less tensioner force and that keeps belt life higher.

[david sammartino]

And so we could go on forever and begin comparing designs and a million different setups. But.....No need to over complicate or reinvent the wheel here, i quite clearly understand your point and the technicalities of it all, quite simple really and anyone who has studied anything about engineering or read a gates belt book can understand the reasoning and how it all works, but like i said again, proof is in the pudding really, and if you have the time to sit down and do these extra things i have no issues, but id rather spend my time designing go fast bits or a solution to something more problematic.
Once again not taking anything away from your work, just dont see the point imo

As for the 164 24v, i presumed i didnt need to list every nitty engine model and so forth, and presumed by 24v i covered the general area. Simply the 12v has more belt strain due to the oil pump, so i dont think we can even compare the designs you are refering to. Imo only naturally.
Alas if i was running bathurst and i needed to be super dooper sure, and i had to run another tensioner i would prefer one on either side of the pulleys as thats were there seems to be less wrap. Having said that id have a dry sump, etc etc and it would all be simpler again. Were does it all end lol

Really all in good fun anyway. Cheers

As for the toyota v6, they can keep their belt wrap and whatever else, i wouldnt touch one bc i dont wear cardigans

[Al Campbell]

Duk,

Good effort. Isn't this one of the reasons that some of us like ALFAs? We see something that isn't quite right and try to make it better. "I can fix that".

Al.

[Duk]

Al,

I know it's not the same same for everyone, but that's the way I see it. If it removes a question about durability/reliability then it makes the cars even more enjoyable because there is less time fixing and more time driving.