That's the attitude! Beat that sucker down. Anyway, since this is such a puzzle, just for laughs and giggles I'd try Dave's way of head on cams shafts off and do the leakdown. You would have access to the top of the valves easy too and could wiggle on them easily just to see if you could change the readings. Also camshaft off would make it easier to play with piston position in the bore on the bad cylinders to see if there are any changes there too. Something weird is happening and really there are only a few places for the pressure to go which makes it even more of a puzzle.
Nothing wrong with my equipment nor my process. Been doing this for too many years and the pros on here understand what I am trying to achieve. Gather accurate repeatable and documentable information is an important part of my work ethic.
Gosh Sorry I tried to help! With everything perfect...there must be nothing wrong I will not waist your time again Dave Bentley
my opening post laid out the situation. there is something causing distortion when torquing down thw cylinder head and therefore air leakage past the valves both intake and exhaust. yes, the gauge, actually all 3 of them give consistent readings for both people that have watched the test, the leak is easily felt out of the ports. Off the block the head is as tight as a drum with both pressure test and vacuum test. I am measuring several things at the moment, following a hunch having found that the oiling dowels are sized very specifically seemingly. possibly they have interchanged side to side and the 0.020" difference in length is causing problem. The 'Italian' fix suggested above might possibly have worked but, I need the answer to the problem, not just for the problem to mysteriously go away. Redos are expensive and lengthy, this is the type of thing that many on this forum are quick to overlook, the RESPONSIBILITY and ACCOUNTABILITY of a pro shop. I chose to do this publically, maybe I should just go back to PMs.
Exactly. We all learn when problems like this arise, only if we work to find the cause of the problem. I actually did the head work and am very much interested in what is causing the problems. Bench tested, the head checked fine with my equipment and when Brian found the problem everything was checked again, and again. 3 different leak down testers don't lie. Plus vacuum tests and the old "solvent in the ports" test all showed fine, off the engine. Hopefully, Brian will find the problem. I'd hate to think that all Diablo heads when torqued on an engine exhibit the same distortion and leakdown numbers.
Well this could be a very italian issue. Their cars are really very notorious for slap it together it will run kind of mentality. I always think Ferrari is bad. I would never own a lambo. Just a WAG coming from my pea brain....If the factory head gasket is that typical old school fiberous asbestos looking thing it would not support the head well if you could torque the head and distort it. Perhaps if you did try the multi-layer steel head gasket it would allow the flat head to sit right on the flat deck and since the steel would not compress perhaps resist head torquing distortion.
FBB- You are on the right track, you Ferrari guys should be proud. Comparing these heads to Ferrari heads- Ferrari heads= Rolex watch Diablo heads= sundial
A common (?) problem seems to be the failure of oil line, either the car burns up or the engine runs out of oil. This one did the latter. One head has had a journal repaired, new cam, both heads have been gone through, a couple of valves replaced, all new bearings, crank checked and polished, Rings were OK, checked and refited.. Car has under 15K, ran synthetics changed every year. the owner drove the car ignoring the oil light, then called me. Engine R&R, teardown repair as nec plus replace any old lines hoses, clutch/flywheel etc etc $25K+
Which cam journal? Did you weld up the cam journal and line bore? Any photos? I've got a head that had an oil starvation problem that needs this.
I'd love to see the thing to try and figure it out but I'm not flying a couple of thousand miles for the privlege. I get asked, begged, conned and cajoled but won't let one in the shop. Life's too short. Good luck Brian.
The valve seats are distorting when the heads are bolted up. Pretty common on some engines. I would recommend doing the valve job over with a torque plate (you would need to make one for this engine) and head gasket (gasket doesn't need to be new for this). Cometics may help but you would need to resurface the block perfectly flat (no sleeve protrusion) for any MLS head gasket to seal. I got Cometic to make the 308 head gaskets by the way and Nick had them make gaskets for some of the other more popular engines. Steve
I just need to identify the cause for distortion. The rear location dowel also serves as a feed for the cam oil. There is n o-ring as well as the gasket at that point. The pos gasket is not located very well at this point. As I've said above, measuring the dowel seems to show it about the length of the counterbores plus the gasket, presumably to help prevent oil leakage (?). I am going to shorten the dowel, polish it's od a little then use some hylomar and cotton in lieu of the o-ring. Thanks for the interest. I've not run into this before even when using a shim steel gasket with a single strand of copper wire superglued around the bore circumference, but that was on a 12:1 lotus twink, 200+ hp. we brits may have electrics that leak smoke and motor/gearboxes that leak oil, but when we build 'em they'll run right and run like scalded apes!
So, how did this all resolve itself? It sounded suspiciously like a 246 Dino valve job, being done for the 1st time, by someone un-familiar in the required useage of honing plates {double-ing as "torque plates"....} ALL DINOs require this process lest the seats leak when heads re-installed. I machine Vintage Ferrari racing engines in my day job, my night job is the making of the parts for my day job, and I am familiar with seeing this sort of distortion... Important issues and concerns.... Are the seats stellite? ARE YOU UTILIZING A SEAT AND GUIDE MACHINE{DCM or Peterson/Berco/Sunnen?)-IF SO, ARE YOU USING DEAD PILOTS, OR , LIVE PILOTS? DID THE SHOP HAVE HONING PLATES? {BHJ??? $685.00ea/2 req'd} Did you hone and bore size the guide bores in the head prior to installing the guides? Did you make each guide, to each of these specifically sized bores?{Okuma CNC for example} How did the seats get replaced-if any as a consequence of loss of valve centerline? Bowl "hogged", or precision contour cuts? Finally, did the finished chamber and ports get evaluated on a bench for flow change(s)? In a car of this type, your specification of tolerances should be =/-.00025, that's plus or minus 2 and a half...TEN thousandths of an inch, for the non-technical out there. This job should have cost $5000.00{NO SEATS, IF MORE WORK REQUIRED, THEN THE BILL GOES UP-DON'T FORGET THE $1300.00 FOR HONING PLATES} or maybe a little more...if not, then you probably have the answer to your question as to why and because outlined above. TO BE CLEAR ON THIS POINT, ..$30.00/guide-48, hone 48 bores/20.00 PER BORE, install and REAM 48 guides-$25.00/guide, , contour 48 seats-$25.00 seat, grind 48 valves-they are all good-right?...$250.00...just about 5k-no?..do the math} This presupposed immacculate heads when they arrive...cleaning is EXTRA! If your machine shop cannot answer these questions, then perhaps a more diligent and proficent practitioner of the art is required! You need to find someone who does these cars regularly(that would NOT be me/us, we are a Ferrari shop) The gentleman who touched on this particular issue-steve race engine I think, is the only other poster on the path of results so far...that I can see.
thanks for the reply, interesting observations. No guides or seats replaced, 2 new valves (in the poor # cylinder). But I found that the dowel which both locates the head and supplies restricted cam oil feed is both very tight and maybe a little too long, I am measuring all once more later today. I will mock up with the old gasket and see if the problem was there.
well I thought I heard it all until I read this thread which confirms I don't know **** glad I'm not a mechanic. would be story at 11 very interesting read though. hope it all works out pics?
I wonder if this might be a variation of what we just identified. Brian, what type of head gasket are you being supplied? Shoot me a PM if this is still evading you.... identified another weak link in the chain a week ago.
