Douvrin PRV V6 engine cams

[Graeme Purches]

Hi there
I saw your post from way back about odd-fire cams on the PRV engine, and an attachment by OddFireV6 who I cannot seem to locate.
I am in New Zealand, and managed to get a grind spec from the UK for my Alpine GTA D500 (2.85 atmo, carburettor), and Franklin Cams here in NZ have ground two sets which both worked fine on two other cars, one mine, and one another chap.
We have now had another set ground for my second car, but had trouble setting them up.
The engine concerned has had head swaps, with the heads fitted modified by a head expert Lindsay Rodgers here in NZ (now retired and unable to be traced).
Those heads were originally fitted to a car that threw a rod, and were purchased and fitted by the owner before the guy I bought the car off. He too is now untraceable!
When my recon guy stripped the engine (he did the other two cars as well) he did not mark the cam timing location before disassembly, as he knew the standard timing procedure which had worked fine on the other cars.
We now believe the cams in this car came with the heads, and that those heads were off an even-fire engine.
I have been advised that the 2.5 litre even-fire cams are identical to the 2.85 litre odd-fire cams, but the cam gears are different, meaning the cams cannot be timed using the standard method.
I note from your Volvo cam spec sheet, that there appears to be a different between the A and B bank settings, which is confirmed by a German manual I have, although the numbers there appears a long way different to ours.
Do you know what the actual difference in timing should be between the A and B banks on an odd-fire engine?
We have had adjustable cam gears made, and would be setting up at full lift.
The specsheet for the cams specifies both the lift at cam and the lift at valve with 1.5 rockers.
Any help or thoughts would be appreciated.
Regards

 

[Aln]

If you set up the cams so that at TDC on overlap the valves on that cylinder are compressed an equal amount, approximately 2mm depending on the size of the cam, and you won’t be too far wrong. The bigger the cam the larger the overlap lift. On an old SOHC race BMW I have, it has over 5mm of lift at TDC on overlap. To be 1 tooth out is very noticeable when checking this way.
Mostly engines like to have their cams slightly advanced, too much and you will have a torquey engine that won’t rev. Retarding the cam will in theory give better top end whilst losing some midrange, but I have found it just loses power everywhere.

 

[Rally]

Hi there


We have had adjustable cam gears made, and would be setting up at full lift.

I am interested in how and who made your adjustable cam gears made .

 

[PeterT]

Do have any grind information from Franlins? If so, it will be easy enough to work out the lobe centrelines and use that for the initial installation point. Then you can fine tune with the verniers.

 

[Graeme Purches]

If you set up the cams so that at TDC on overlap the valves on that cylinder are compressed an equal amount, approximately 2mm depending on the size of the cam, and you won’t be too far wrong. The bigger the cam the larger the overlap lift. On an old SOHC race BMW I have, it has over 5mm of lift at TDC on overlap. To be 1 tooth out is very noticeable when checking this way.
Mostly engines like to have their cams slightly advanced, too much and you will have a torquey engine that won’t rev. Retarding the cam will in theory give better top end whilst losing some midrange, but I have found it just loses power everywhere.

Thanks for this
Much appreciated.

 

[Graeme Purches]

Do have any grind information from Franlins? If so, it will be easy enough to work out the lobe centrelines and use that for the initial installation point. Then you can fine tune with the verniers.

Thanks Peter
Much appreciated

 

[Graeme Purches]

I am interested in how and who made your adjustable cam gears made .

My son, who is doing the work, found an older guy here with water cutting gear. He actually had two guys with the gear look at the job, but the first was reluctant to do it, because it would be easy to stuff up and he was also worried about clearances.
The guy that did the job took a couple of months to deliver the goods, but it has worked out fine - basically he split the original gears, made a face plate with bolts, and water cut as required the gear behind to give adjustment slots. I have attached a link, where you will be able to see some pix of the setup. Sorry, but do not have an actual drawing, but this will give you the idea.
https://photos.app.goo.gl/yq4pEsM3eK6Y7pT29
Cheers
Graeme

 

[Graeme Purches]

Do have any grind information from Franlins? If so, it will be easy enough to work out the lobe centrelines and use that for the initial installation point. Then you can fine tune with the verniers.

Yes we do.
Thanks Peter
Appreciated.

 

[OddFireV6]

Hi Graeme
Sorry I could not be found, you have generally good advice from the blokes above. Because it is difficult to grind cams to get an accurate bank to bank timing re=ground cams are often not very good. To get around this I used a degree wheel as you have and two dial indicators. I created a table that considered lobe centres opening at 50thou on the valve and closing at 50thou on the valve, I then redid this at a range of lifts to get consistency. From this I calculated the overall advance or retard of the cam. This is done, just for the timing process, with large valve clearance settings, say 15 thou on inlet and exhaust. No idea which engine this was but it was a long time ago.

The 5 degrees advance is excessive here, go for square timing to 2 degress advance.

LH Cyl 3	Inlet	BTDC	ABDC			lobe ctr		cam adv
mm	Thou	Open	Close	duration	overlap	ATDC	lobe sep	retard
0.025​	0.001​	33.5​	57.5​	271​	58​	102​	107​	4.8​
0.254​	0.010​	26​	50​	256​	43​	102​	107​	4.5​
0.508​	0.020​	21​	44.5​	246​	33​	102​	106​	4.5​
1.270​	0.050​	11​	33.5​	225​	13​	101​	106​	4.8​
1.788​	0.070​	5.5​	27.25​	213​	2​	101​	105​	4.8​
LH Cyl 3	Exhaust	BBDC	ATDC
mm	Thou	Open	Close			BTDC		4.7​
0.025​	0.001​	66.5​	24​	271​		111​
0.254​	0.010​	59​	17​	256​		111​
0.508​	0.020​	54​	12​	246​		111​
1.270​	0.050​	42.5​	1.5​	224​		111​
1.788​	0.070​	36​	-4​	212​		110​

 

[Graeme Purches]

Hi Graeme
Sorry I could not be found, you have generally good advice from the blokes above. Because it is difficult to grind cams to get an accurate bank to bank timing re=ground cams are often not very good. To get around this I used a degree wheel as you have and two dial indicators. I created a table that considered lobe centres opening at 50thou on the valve and closing at 50thou on the valve, I then redid this at a range of lifts to get consistency. From this I calculated the overall advance or retard of the cam. This is done, just for the timing process, with large valve clearance settings, say 15 thou on inlet and exhaust. No idea which engine this was but it was a long time ago.

The 5 degrees advance is excessive here, go for square timing to 2 degress advance.

LH Cyl 3	Inlet	BTDC	ABDC			lobe ctr		cam adv
mm	Thou	Open	Close	duration	overlap	ATDC	lobe sep	retard
0.025​	0.001​	33.5​	57.5​	271​	58​	102​	107​	4.8​
0.254​	0.010​	26​	50​	256​	43​	102​	107​	4.5​
0.508​	0.020​	21​	44.5​	246​	33​	102​	106​	4.5​
1.270​	0.050​	11​	33.5​	225​	13​	101​	106​	4.8​
1.788​	0.070​	5.5​	27.25​	213​	2​	101​	105​	4.8​
LH Cyl 3	Exhaust	BBDC	ATDC
mm	Thou	Open	Close			BTDC		4.7​
0.025​	0.001​	66.5​	24​	271​		111​
0.254​	0.010​	59​	17​	256​		111​
0.508​	0.020​	54​	12​	246​		111​
1.270​	0.050​	42.5​	1.5​	224​		111​
1.788​	0.070​	36​	-4​	212​		110​

Thanks heaps for the advice.
Will let you know how we get on.
My son is flat out at the moment but should be back on the case in a week or so.
Cheers
Graeme