B6 Camshaft Mechanical Fuel Pump Lobe Help

[drddan]

All the threads i've read, says the mechanical fuel pump lobe is still there on the B6.
Well...SOME of it is there! It is not as WIDE as the B3 fuel pump lobe.

See here. In the pic, the B6 cam is sitting on top of the B3 head above the B3 cam. You can see the arm of the mech. fuel pump resting on the B3 fuel pump lobe. The B3 lobe is much wider.




So I have this question now.

Is that enough to run the mechanical fuel pump?

I took the B6 cam out to polish the pump lobe.

[zoe60]

That's why I used my original B3 cam. I think it would work if it were machined smooth but that rough surface would wear out your fuel pump arm quick. If you read my post, mine makes a squeaking noise now. If your B3 cam is in good shape you'll probably have to use it. I would like to get an Aspire cam and the roller arms and have a fuel pump lobe machined onto the cam. Either that or get an electric pump. Mine's been running great with the B3 cam. The noise just started and it's possible it's not even the cam. May just sound like it is.

[drddan]

Arent the grind on the cams different? B6 vs B3?

I have the B6 cam out to polish the lobe smooth.

[eurotiva]

Tom can get you an electric pump for $35. Mr Gasket brand @ advance auto parts.

[drddan]

I measured the lobe height's B6 vs B3.
There is a difference in the measurements. I dont have the specs on the cam grinds at the moment, but the measurements I got with a micrometer are:

B6= 1.431 over the high point of lobes

B3= 1.419 over the high point of lobes

...with the "round" diameter being 1.220, about the same for both B3 and B6.

That is a diff. with the B6 cam lifting the rocker .211 and the B3 lifting the rocker .199. for a extra .012 lift for the B6.
Of course my B3 had 250,000 miles and the B6 is supposed to have 100,000 miles, so could the B3 lobes could have worn that much?????

[drddan]

Tom can get you an electric pump for $35. Mr Gasket brand @ advance auto parts.

Yes he can!
I am looking into my next move.

I can turn the B6 cam lobe at work on a lathe and 4 jaw chuck

...or get an electric pump.

Hmmm...decisions....decisions :p

[FestYboy]

lobes should never wear, and if they did, they'd be showing the raw casting. as far as the fuel pump lobe, make it smooth-ish and run it, the width shouldn't affect it's performance.

[zoe60]

The measurements are interesting to know. I guess I assumed they were the same since you can use the FMS cams in B3's or B6's. Wish I had my old B6 cam back. Wonder how much difference 12 thousanths would make?

[drddan]

.012 x ratio of rocker. Not sure what Mazda/Festiva has for that.
Usually 1.6 - 1.7 which is .019 - .020 lift at the valve.

Of course, this is all conjecture, since I am doing this in my head and i'm not sure of the ratio.

I would venture to say, better MPG with B3 cam, and better performance with B6 cam?

I think the FMS cam is a performance cam, and prolly has more lift?

[zoe60]

Well shoot. I guess my Aspire cam idea is definitely no good then. I remember thinking about machining the surface smooth on mine but wanted to hurry up and get done. I guess you would be smart to take the time to do it. It would probably be best to keep the original cam in the original head. They've gotten used to each other. Wish I had kept mine. I end up throwing out stuff I don't think I'll ever use. Good luck Dr. Dan, maybe we can race someday! lol

[bravekozak]

The cam lobe for the fuel pump is eccentric. You can't just turn it on a lathe. I am surprised the fuel pump cam isn't ground. You may have to do the same as me. Electric pump with a bypass pressure regulator.

[blkfordsedan]

I don't believe there is any difference between the B3 or B6 camshafts, as long as they're both mechanical or both hydraulic (at least replacement part numbers are the same). I don't know what year your B3 is, but if you're comparing an early mechanical cam to a later HLA cam, then there very well may be some difference. The ramp profiles and valve acceleration speeds can be different between the two designs, so don't get too caught up in worrying about total lift. It's also possible the mechanical rockers have a different ratio. I've only measured the HLA rockers, so I can't say for sure. If you have the mechanical B3 cam, I would use it, along with the adjustable rocker arms and be done with it. You'll never notice a difference in performance, and at least you'd never have to worry about sticking HLA's. Otherwise, run the B6 cam, HLA rockers and an electric fuel pump.

The hydraulic B6 cam should measure .213" lift @ the lobe. Depending on wear, factory grinding tolerance and what you used to measure it, (dial indicator, micrometer, caliper, etc.) you can easily be off by a couple thousandths. The rockers are variable ratio due to the follower design, but at max lift they give ~1.75:1 ratio for a valve lift of ~.373".

[Movin]

The cam lobe for the fuel pump is eccentric. You can't just turn it on a lathe. I am surprised the fuel pump cam isn't ground. You may have to do the same as me. Electric pump with a bypass pressure regulator.

He said four jaw..

[BigElCat]

I'd stick with a mechanical fuel pump, no matter what it takes.

The B6 fuel pump lobe would have to be done on a cam grinder, and the surface rehardened.

Is the FMS cam made for the HLAs?

[FestYboy]

FMS cam can accept the mechanical and hydrolic rockers (both have the same style follower)