ALFAGTV6.COM

[ChrisS]

How can you work on that like that???? There's no crack showing???? You can't possibly work on an Alfa without crack!!!!

I can if it's -2C and I've been out in it for 6 hours!! I'm not a young man any more don't you know...us old 'uns need to keep wrapped up and warm

[Zamani]

-2 C ??? That's a bit cold innit?

[MD]

Oh Romeo, 2C* or not 2C* the Crack, that is the question.

[MR2 Zig]

rotfl!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[ChrisS]

I do like the humor on this site!

[MD]

Yeah Chris, you gotta watch these guys. Half of them are bed wetters and the rest are simply bent. Me, I am the only straight one here

On a less sane note, I did a stint in the UK and I can clearly remember freezing my credentials off working in the gutter repairing some sheit box just to get to work. Being a renter, I never owned a garage and had to endure the cold- something all you guys living on the upside down part of the planet can relate to I am sure.

I haven't had a chance to express my congratulations for all your hard work so I thought I better chime in soon..

..and BTW the worst of the bunch is that SAARF AAfrikani Kevin-he'd wet the bed if he had one..

[ChrisS]

I'm saying nowt about folks sanity or lack of it - after spending 3 consecutive weekends, in -ve temperatures, taking the same gearbox out and putting it back again, on a car I don't normally drive in winter, I don't really feel I've got the right

Trouble with our weather is it's usually just not that bad or that good. If it had been -10C or lower I wouldn't have contemplated the job - I'd have had the good sense to stay indoors. As it was, I figured why not. Mind you, we did get -13C the other day, but I've yet to experience anything worse than the -55C when I went to Moscow back in 1977 (or 76 or 78, I forget). That was proper chilly that was.....

[Mats]

Nippy...

[ChrisS]

Right then chaps....I'm hoping for some genius help here!

This 12V engine of mine.....it's great above 3k or so, but at lower revs, it sounds and feels harsh. Almost as if it's a balance or mis-fire problem, but it smooths out as the revs rise, it's driving me to distraction and I'm running out of ideas.

Things I've tried so far to no avail;

Compression checks - did one at about 50 miles and again at about 250. Figures identical and matched cylinder to cylinder within a PSI or two.

New plugs - old ones looked fine anway.

Tweaked the mapping in the problem area - so far I tried adding a load of fuel, then a load of timing - neither made any difference. I've yet to try removing fuel though, will try that next. I also need to check if I set the ECU to cut fuel on overrun, as it still exibits the problem off-throttle as far as I can tell. If fuel is cut and the problem is still there, then it can only be something basic and mechanical...surely.

After reading a post about the V6 having a vertical balance component, I started to wonder if maybe the balancing method hadn't detected this, so thought I'd try putting a 3l flywheel on, rather than the 2.5l flywheel just in case there was a subtle resonance thing going on. Made no difference at all. (But I don't really think it's a balance thing anyway).

Next I intend swapping the injectors in case one has a bad spray pattern.

One suggestion I had was to fit the blower and see how it behaves under boost at these revs. Might try that too. The blower setup is rigged not to boost until about 75% throttle, but it's easy enough to change that, so boost comes in a lot earlier, if only for testing.

I also wonder about the combination of the cams and the exhaust at lower revs perhaps?? Cams are low overlap (for the supercharger) and the headers are reworked 24V items, so a wee bit bigger diameter, but primary lengths are very close to stock cast. I'm wondering if there could be some problem due to poor scavenge under these conditons that goes away as revs pick up??

Next will be to try some other cams, then refit the old exhaust which has cast manifolds and smaller pipework.


If I still can't find the solution, I will have run out of things to try so will have to pull the engine and strip it. If it gets to that stage, I will be tempted to give up on the supercharged goal, sell off any parts I can and just put the aspirated engine I took out, back in.


I don't get why it is so smooth and runs so well at higher revs, yet is so grumpy lower down. The engine mounts are pretty stiff (some 70 Shore wishbone bushes), so will transmit pertty much everything from the engine into the chassis and it's this that makes me doubt it's a balance issue (plus the fact I had the whole engine balanced to 0.28gmm).

Is it possible for piston seal to be OK for a cranking test, then go bad at low revs, then come good again at higher revs????

As you can probablay see, I'm getting desperate for ideas here.....clutching at straws doesn't even come into it!

All thoughts welcome as I'm going round in stupid circles with it and it's really p155ing me off now.

Thanks.

[ar4me]

I would double check cam timing to make sure you didn't jump the timing belt. You are so close, don't give up, keep at it!

Probably obvious as well, but I would make sure there are no air leaks.

Jes

[ChrisS]

Thanks Jes, I was sure I had the timing right....but it can't hurt to do it all over again to make sure.....and to be fair, it does have a somewhat similar feel about it in some ways to when my last engine had a cam timing error...but that one never really liked to rev, this one is fantastic. That one I relied on the cam cap marks, and one of them turned out to be a tooth out. The scribe marks were right though.


As a sanity check for me, this is how I timed it up Yell if I screwed up.......

I set zero lash on #1 & #5 inlets, I found true TDC using a large protractor on the crank pulley and a positive stop on top of #1, splitting the difference measured going clockwise & anti clockwise. Reference pointer bolted to the block.

Using the timing numbers from the cam grinder, I then measured 0.050" lift at the cam follower, using a DTI and with the probe at 90 degrees to the face of the follower. I checked both sides of the lobe (valve opens and valve closes crank angles) to make sure I had it right. Turned it over a few times then did it again to make sure. Did both cams this way.

Once I was happy, I then looked to see where it had come up using the scribe marks on the pulley hubs and the 164 timing template - very close to the 70 degree marks on both heads FWIW. Also very close using the cam cap marks (not like I believe those any more though!). I realise this may not mean anything as such, but AFAIK, the cams are ground to the original marks so should at least be close, although I have used vernier pulleys to get them spot-on to published spec.

I re-checked timing using the template and my previously established template reference marks and no movement - both cams as I set them. Sadly!

Also checked for leaks - nothing found

I've taken the day off tomorrow to once more remove the gearbox...while putting the 3l flywheel in on Saturday, I thought I'd install the 6 puck cerametallic clutch plate now I've had it modified so it all fits together.....it horrendous. Shocking judder on takeup, so that's got to come out again. I figure I may as well re-fit the lighter flywheel while I'm at it, given that fitting the 3l one made no difference to the harshness.


Keep 'em coming chaps.

[ar4me]

Do you have a wideband o2 sensor and portable meter like the innovate motorsports setup:
http://www.innovatemotorsports.com/products/lm2.php
for measuring air-fuel ratio? With the WBo2 sensor in the exhaust clamp you can hook it up in 2 min and measure/log while driving/idling/etc. to make sure fueling is about right in the trouble area.
Jes

[Zamani]

I think a balance problem will manifest itself in the higher rev range. That said I don't know what is going on. Maybe just fuel mixture? Too lean in the low revs? Get the wideband A/F as per Jes.

Ignition too retarded or too advanced?

[ar4me]

Another suggestion is to check your fuel and ignition maps. With a different standalone engine management system I have seen what can be perceived as "rough" running if there are spikes/outliers/non-smooth regions in the maps. Though, not sure if this applies to your system...? Just a thought...
Jes

[kterkkila]

Have you checked the exhaust temperatures on the different cylinders? If it's running harsh at let's say 2500 rpm, you could run it on that rpm for a while and then check the temperature of the pipes near to head with infrared. If one is giving significantly different readings, there could be different air fill on cylinder, or different fueling.