Importance of verniers

[oilyhands]

I have recently installed a set of 1320 cams in an 1800K series engine and the owner asked me if verniers were really neessary.

 

As an exercise I thought it might be interesting to measure the cam timing on his standard cams with standard pulleys, then measure the 1320 cams with standard pulleys before fitting verniers and timing them correctly.

 

The lift at TDC for the stock cams should be inlet 25 thou, exhaust 25 thou.

 

For the 1320 cams should be inlet 75 thou, exhaust 65 thou

 

Here are the results obtained

 

Cam setup inlet lift exhaust lift

Stock 4 thou 41 thou

1320 stock pullies 13 thou 109 thou

1320 verniers 75 thou 65 thou

 

As you can see the cams were a country mile out, mainly due to latency in the belt system and secondly due the the fact that the 1320s are not designed to be timed on the standard 110degree lobe centres.

 

I have also recently measured a set of superpsort cams installed with the stock pullies prior to me upgrading to verniers

 

The recommended lift at TDC for SS cams is inlet 70 thou , exhaust 60 thou.

 

The actual measured lift was inlet 6 thou, exhaust 94 thou.

 

Om the inlet that is less than a quarter of the recommended lift for the stock cams!!

 

Conclusion.. verniers are absolutely essential however accurately the cams are ground due to inherent lack of accuracy in the stock system. Even the stock cams were approximately 10 degrees out with the stock pullies.

 

The 1320 exhaust with stock pulley was very baldy retarded, enough for the valves to get dangerously close to the pistons.

 

The SS cams were both very badly retarded, around 14 degrees (almost a complete tooth)

 

Dave

 

 

 

Edited by - oilyhands on 25 Nov 2011 21:56:45

[Sheds Moderator]

That is miles out. Recently you were talking about fitting offset cams with a dowel, how easy is this to do one std cams?

 

Secondly, how far out is cam timing on production engines? Is it worth doing a cheapo dowel offset mod on a standard cooking car?

[Fishy Dave]

Thanks for posting Dave, interesting stuff. In terms of power and torque how much difference is this making by having the cams so for away from ideal timing?

As an aside, how much more power do the 1320s make compared to the supersport cams (assuming no other modifications fitted)?

[Wrightpayne]

Oily,

 

With recent posts about pulley wear would you be able to achieve correct timing in these cases with offset dowels?

 

 

I used to time my BLMC A series cams (MD296) with offset woodruff keys rather than verniers.

 

Regards

 

Ian

[Sheds Moderator]

FishyDave, the benefit of verniers is in the midrange. My 1.4 (that you know well!) had no verniers and I'd had the head skimmed. This puts the timing slightly out so verniers are an even better idea. You will remember the flat spot about 2000 rpm, I know I do, and verniers go a long way to improve this. Top line power is the same. Interestingly, RAC seals are attached to the cam cover so you can't fit verniers on the race sealed engines.

[Golf Juliet Tango]

This tells us an awful lot about standard K engines. I wonder how inconsistent they were (when they were still in production) and how inconsistent other manufacturers' engines are.

Maybe every engine might benefit from some induvidial attention but are (insert your favoured engine maker here) so way off standard?

Has anyone else done these measurements on other engines?

[Jason Plato]

but it's also worth checking if you only need one vernier, there is a chance that the cam timing can be achieved with one hole tooth movement of the STD verniers.

 

[6speedmanual]

When cams with more lift, duration and overlap are used, timing becomes more critical, for various reasons.

 

The level of variation inherent in the cam drive system may be relatively unimportant in its effect in a standard production engine running 'mild' cam profile and timing. Therefore may not have been a good area to invest design effort and manufacturing cost.

 

 

Peter

[Stationary M25 Traveller]

Oily told me that all K-series engines were built by Rover with the timing some 8 degrees out - presumably for economy or emissions ?? He fitted an offset dowel on my inlet cam 1.8 VVC) which improved things enormously. Can't fit verniers on the VVC. Also changed the exhaust can to one with longer duration.

 

Gave a huge boost to mid range grunt

 

Where has the Thumbs Up smiley gone ? It has turned into a notepad on my phone

[6speedmanual]

I don't think they were assembled specifically "out" to achieve any particular effect.

More that the assembly tolerances allow such a range of deviation.

Becomes significant with performance cams.

 

Peter

[Golf Juliet Tango]

Oily told me that all K-series engines were built by Rover with the timing some 8 degrees out

Ian, firstly I don't see that that makes any sense; secondly, from what I have read they were incapable of achieving consistency of output and that timing varied considerably.

[myothercarsa2cv]

Oily, or any other knowledgeable fellow, should we be thinking about verniers on standard EU3 1.6's?

 

Also, with all this talk of pulleys being made of cheese, wouldn't we be better off leaving it if we have a standard engine?

[Sheds Moderator]

I remember Oily explaining in the past that the crank pulley is the source of several degrees of variation, it's not a conventional keyway so there is no precise positioning until you have tightened the crankshaft bolt. In addition fitting offset dowels to normal cam sprockets will get round any wear issues, I imagine the originals are steel. Mine look like it, they are just machined grey cast metal, I can't remember whether they had rust stains that would mark them out as cast iron/cast steel.

 

WRT to eliminating production variation, this has been going on for years, it's termed blueprinting. Back in the days of sand castings and hand finished parts I think there were huge gains to be had simply by putting the things together as intended. These days less so as things like die casting, CNC and probably emissions regs mean that batch to batch variations are low. Nevertheless a mate had a 1600 Golf Mk1 GTi which was blueprinted and he reckons it was significantly quicker than the mass produced ones. No insurance hike either. Is it standard? Oh yes. Very standard.

[LesG]

BOSS I can second that with my experience. I had an ex-VW VR6 Vento Cup (I re-shelled into 3 door Mk3 Golf) car with a (Minister no less!) blueprinted engine.

Putting out (only) 188bhp and weighing 1020kg with 1/4 tank of fuel, it was significally quicker than similar cars with more power. The engine was (and stll is) silky smooth with a huge torque range, and consistently embarrassed far more exotic/powerful/expensive machinery at the many trackdays I did.

 

P.S.- must get those brackets made so I can fit my verniers to my SS 1.6 over the winter! Big to Oily!

[LesG]

Meant to add; I'll publish my cam timings before and after verniers once I've sorted it too.

[Sheds Moderator]

I made a set of brackets for a K and they were circulating in exchange for a NtL donation. Last I heard Tony Whitley had them, the deal was that you passed them on when you were done and dropped a couple of quid in the NtL pot. I'm sure they are still out there somewhere, a wanted or a post here would pick them up. It would be good to have them used again.

[jakeandlizzy]

I just had my 1320s timed and the correct setting was achieved with the verniers almost at the limit -- we almost considered skipping a tooth and going the other way, but we got there in the end! so yes, I agree!

[oilyhands]

From experience the cams on a K series are reatarded by around 6-8 degrees. There are many reasons for this, variations in block and head thickness is one, but the prime reason is the slack on the 'D' drive that locates the bottom sprocket to the end of the crank. Everytime the cambelt is replaced, the bolt securing the pulley is undone and the sprocket cam moves introducing further changes.

 

In the worst case I have measured 8 degrees of slack in each direction giving a total variance of 16 crank degrees between the pulley at the furthest anti-clockwise position compared to the pulley at its furthest clockwise position.

 

Whenever the belt is changed or the head skimmed, the timing needs rechecking, it is less significant on an engine with stock cams as there is reduced danger of valve/piston contact, but on a VHPD/R400 there is an ever present danger of the exhaust valves kissing the pistons.

 

Oily