Rebuild Finished Mystery - Hesitation every 120 Degrees

[wdfifteen]

Originally Posted by tmaull

Bruce, who is rebuilding the engine in my car, has finished with the build, but there's an issue that he hasn't seen before.

I'm not comfortable with this play-by-play criticism of a mechanics's work. An honest retrospective on the part of Bruce would be great. I'm sure Bruce would be glad to post the results of his analysis of the resolution of this issue.

[RedCoupe]

Originally Posted by wdfifteen

I'm not comfortable with this play-by-play criticism of a mechanics's work. An honest retrospective on the part of Bruce would be great. I'm sure Bruce would be glad to post the results of his analysis of the resolution of this issue.

Sorry, but I don't see criticisms of Bruce's work. Just some people offering suggestions and trying to help. I for one have read many of Brice's posts and threads and it's obvious that he is a talented guy with a lot of knowledge. We all want this to have a good ending.

[Flat6pac]

I'm building something that others have had their hands on and reflection on the work done has me a bit confused.
I posted up the 010 stamping and the first response had to do with cutting the case for cylinder base. Turns out it's a turbo case with 24 old dilivars. My thought was, no, no one would reinstall 24 old dilivars studs after doing machine work. WRONG..
Crank mains had Porsche bearings dated 2/89 so they were original, not center lined bored and resized.
The resistance at each 120 degrees was a concern, realizing the 2 Pistons at that point are changing direction.
Set motor up with enough install to run. Turned it over for oil pressure, there was no noise from Pistons changing direction...good. Added spark plugs, got it to light off.
Sounded like an army Gatling gun on the helicopters.
Engine is out, I'm making comparisons and checking visuals.

1st comparison pictures
Notice cam nose is sitting inboard in chain box
2nd comparison picture 3
Notice 3.2 cylinders. The one to the left carbon deposit above the ring is from a stock 3.2. The one on the right is from this engine when I took it apart. The carbon deposit is narrower. Driving the piston higher because the case spigot is shorter.
Bruce

[Spenny_b]

Originally Posted by wdfifteen

I'm not comfortable with this play-by-play criticism of a mechanics's work. An honest retrospective on the part of Bruce would be great. I'm sure Bruce would be glad to post the results of his analysis of the resolution of this issue.

?? I honestly didn't read it as a critical post at all. As mentioned above, Bruce is one of the Forums good-guys, we know that - I just assumed from my initial read the other day, that Bruce and the OP were scratching their heads and throwing it out there for any suggestions.

ETA - ....and I'm thoroughly intrigued to find out what the answer turns out to be...

[0396]

Im sure this will be resolved by Bruce. But if I understand it sounds like the two pistons were taping their respective heads.

[KTL]

So it's a combination of the case spigots being cut, along with the heads being resurfaced too? That picture of the chain case is good reason why people should send their chain cases with their heads. When the heads are cut, the cases can be cut the same amount and your cam snout will remain centered in the opening.

Problem with cutting the chain cases is that it moves the sprockets further inward and creates more slack in the chain. That additional slack gets accounted for by the chain tensioners. But they can only take up so much slack. Sometimes a larger idler sprocket is needed to ensure the tensioner can do its job w/out being extended so far out.

Looks like to me that the combination of cams with the higher timing/overlap spec and the cut down spigots + heads is the issue. A friend & I timed a set of 964 regrinds on his stock 3.2 top end (high mileage motor that likely had multiple previous head work) and we encountered resistance when started out base timing with the dot/930 positioned up. Had to back off the cam to allow us to get started in our first reading of what the initial timing was.

[tmaull]

Just to be clear, this is NOT a criticism of Bruce's work. I'm EXTREMELY happy with Bruce's work - and would recommend him to anyone, as well as use him again in a heartbeat. I gave him a weird engine, with stamping we didn't understand, and then we put some even weirder parts on it. We came across an issue that we didn't understand at the time, and I wanted to share the issue in case there was a similar issue that the hive-mind had previously seen, or if not, share this one so that people could search for it in the future.

So, I'm not sure if this is clear from the earlier posts, but here's our working theory. The 010 stamping indicates that the case was cut down by a full 1mm. When I purchased the car, it was advertised as having a "Euro" rebuild. I think what happened was the previous rebuilder, instead of sourcing correct 3.2 Euro mahle pistons, used standard 3.2 mahle pistons, and cut down the deck to get a higher compression ratio. So we are adding thicker base gaskets to get some additional clearance, lower the CR, and hopefully get the result we were looking for.

Again, just to be 100% crystal clear, Bruce has been one helluva mechanic, on what I think is a who-dun-it of an engine build.

[Jeff Alton]

So what is the diagnosis of the noise created when the engine was started? Valves contacting pistons? Are the pictures posted above pre, or post, rebuild?

Cheers

[Flat6pac]

Piston coming up and touching the head while the piston changes direction.
Bruce

[LJ851]

Originally Posted by LJ851

Could be piston to head or valve interference

I called it back on post 3, where do i sign up to get my prize?



Hope you get this resolved with minimal headache and $.

[Flat6pac]

Measurements against another case I have shows measurements consistent to the case spigots being machined 1 mm. We have ordered base gaskets to make up the cut difference so we're back in line with not guessing what others have done
Bruce

[356RS]

Wow 1mm on the cylinder spigots. That's way more than a little clean up.

[tmaull]

Probably a hack way to increase CR.

[Tippy]

Originally Posted by tmaull

Probably a hack way to increase CR.

Pretty far from a hack. Machining a spigot isn't like using a dremel to achieve the same results. HEHE

[cgarr]

only cases I machine the spigots on are mag cases because they need it and the most taken off is around .005 thou and that's a bad case: