Do head stud bolts have to have exact same torque?
 

I've found that the camshafts are a little tight if I torque all the head studs to 23.5 ft/lbs, but if I tighten the outside cyls a little bit and loosen the center one a tad, it's very free. No other pattern of torquing makes a difference. Should I leave the bolts at different torques, or leave the camshaft tight?

Jeff

Just to clarify, this is only an issue with one of the camshafts. The other one was fine.

Jeff

not having any experience with this I can't answer you, but I can add to the responses to get someone else to look who can. Plus you might check in with Mark at Sportech where you got the head washers from, he will tell you for sure, and he is close by.

Seems if you can quantify "tad" and "slightly" to the actual torque numbers, it would help.

Jim

I don't have exact torque numbers. It was hard to measure with a click-style torque wrench. I just torqued them to 23.5, then loosened them a tiny little bit, maybe a few degrees of rotation. Same for the overtighting of the outside cyls.

I can redo the process and get exact values, what's the acceptable range for these? I've seen different values mentioned, usually proportional to HP.

This is just a 150HP 2.4T street engine so I'm not stressing anything too hard.

Jeff

You want to have all the heads torqued properly and you don't want the cams to bind.

You definately don't want the cam binding. If the cam is binding it will be rubbing on the cam housing bearing surface instead of riding on a film of oil. Bind it enough and you will be flexing the cam until it breaks.

If the heads are not the same heights the cam will bind when everything is torqued up. The proper way to make everything square is to deck the case spigots, make sure all the cylinders are the same height and make sure all the heads are the same height. I bolt the heads on and run a straight edge across the top to check.

If it's not possible to address the mismatch in deck+cylinder+head heights there is a work-around. You can torque the cam carrier bolts (8mm nuts) to different torques. It's not an idea situation but it works. Put the cam in and torque the nuts as you spin the cam and feel for binding.

Before you do that, pull the cam carrier, clean off the sealant, and run a (machinist's) straight edge or piece of ground stock across the top of the torqued cylinder heads and see if they are even. If they aren't, maybe you can swap a "tall" one with a "short" one from the other bank or something. If they are even, clean the sealant off the cam carrier and check that for flatness. Maybe you just got too much sealant on there?

-Chris

EDIT: I said "spin the crank", I meant "cam".

Ok, I'll pull it apart and figure out where the difference is coming in. These are all stock parts so I'm not sure what could have changed, execept the valve job. The machinist said the heads had been previously resurfaced, so maybe there's a short one from that. I did mix up the cylinder numbers, so maybe it's just a case of getting the right 3 on each side.

Thanks!

Jeff

use a large micrometer across the heads, from the cylinder contact surface to the flat area that the cam tower contacts. hopefully they're all the same. 85.5mm is stock if i remember right. most shops cut 0.25mm at a time. then the base gasket which measures 0.25mm is increased to 0.50mm by either doubling them or using a single thick one to compensate for the amount removed. so if they were cut, the measurement would likely be in the 85.25 range. the base gaskets themselves can get squished out of shape too, so they should be replaced in the troubleshooting process.

So I pulled everything apart, and the problem seems to be the case itself. If I put a straight edge along the cylinder mating surfaces, it floats over the center surface about .004". With the cyls and heads torqued down, theres the same .004" over the center cam housing mating surface.

That's bad, isn't it? :(

Jeff

Your magnesium case is warped. Did you get your case checked/measured for case alignment, spigot deck, and main bearing bore tolerances before reassembling? Read Wayne's book and/or search the forum regarding mag case work - you may need as little as having your spigots machined flat or you may need as much as a complete case resize.

please add the year of your car to your signature so we can cut to the chase.

Ok, fixed the sig. It's a '70 T.

It's only off by a tiny little bit, so if there's some way I can shim something or shave something else without having to open the case...

Jeff

You didn't answer the question - did you get your case checked out? If not, then yes, you need to investigate what's going on. If your crank is binding and/or your main bearing bore is off center by 0.10 mm, that's significant and must be addressed. Need more information here.

The case was brought to a machinist, but I diddn't explicitly ask for it to be measured.

Jeff

afaik every mag aircraft engine "must" be line bored at a rebuild.

So, as said before, you have to measure everything out and find out why you're out 0.10 mm. If the case is warped, you'll probably end up having to get Supertec or Competition Engineering to resize the case...about $1k. I've never heard of just the deck being warped but the main bore being straight, but maybe you'll get lucky.

You should read the engine book too, so you'll know what else you've missed. Oil bypass mod, head stud inserts....read the book.

Thanks for the info. I've read the book about 10 times now. Decided against the oil bypass, did the inserts.

Diddn't measure the deck.

Back to step 1.

Jeff

fwiw.. based on my limited understanding of machining the 911 engine I just sent the parts out to Competition Engineering to do whatever is necessary. He wanted to know what I'll be using the engine for then Walt talked me out of work I thought I needed..

There are a limited amount of trully good machinests around for our engines. I wouldn't even consider someone who doesn't have a history with them.

meaning our engines can sometimes be a pia compared to Detroit iron..

The engine ran fine when we tore it down, it just had a lot of easy miles on it. The PO drove it very carefully for 25 years. I just diddn't suspect warping. Is this something that just happens over time, or is it only because of overheating?

Can't you get a 7R case for $400? Why would you spend $1K getting one fixed?

Jeff

Case warping is inherent to the mag cases, it is not necessarily due to overheating.

You can indeed get a 7R case for $400 - but that's going to require a complete conversion to a 2.7 motor due to the wide spigots, unless you find a small spigot 7R (Not likely for $400). Any used mag case you find is going to have the same potential issues as yours, unless it comes with a clean bill of health from a very knowledgeable machine shop. Something else to consider is the value in retaining your case with the car to preserve originality. With the recent skyrocketing prices of early cars, even the T cars, your investment in preserving a 'numbers match' status will be paid back in spades upon resale.

Why not see what's wrong with yours first? It may not be so bad...and Competition Engineering and Supertec are both shops that have the experience to take care of your mag case right, and the integrity to deal straight with you.

PIA? No way. Come on:
-Resize case: $1,000
-New fiberglass shroud from Series 900: $275
-Rebuilt MFI pump: $900
-Spending upwards of $10,000 on a Porsche engine and still having less than 200hp: Priceless