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TiGurr
09-13-2008, 09:09 PM
Hi,

This forum is a great resource! :biggrin:

Thanks to all that regularly contribute to it.

I'm fixing a 1998 Ti for a friend that is in trouble. basically the car lost power and would hardly drive, and produced a loud 'chuffing' sound.

BMW stealer checked it out and found misfire on all cylinders with a compression test result of no compression in 3 & 4.

The stealer quoted £600 to remove the head and check what the problem is.

So I've searched on here, whipped the head off and found the head gasket literally melted away in the thin bridge between cylinders 3 & 4. Cylinder 4's piston top is carbon free, while the other 3 have about 1mm carbon buildup.

The head and block face look ok, but on closer inspection the head has had a LOT milled off the face. The block has been sandpapered too. This can't have been done too long ago, perhaps within the last year.

I had the head checked, and while the face is only about 4 thou warped, the cam cover face is like a banana! The exhaust cam has been running in a bent head, as the rear cam bearing is shredded.

A full reconditioned head is on order including cams :smile:

Just need to clean off the block face & check if that's warped. I hope not. Maximum allowable front to rear and corner to corner is about 4 thou. Across the block is 2 thou.

Will report back tomorrow :confused:

tiFreak
09-13-2008, 09:16 PM
wow, sounds like the PO didn't do a very good job with maintenance, good luck fixing it

TiGurr
09-13-2008, 09:39 PM
No, they obviously overheated it, got a cheap & dirty fix done and sold it as quick as possible while it still ran!

Some people just don't deserve to own a decent car.

Mallard
09-13-2008, 10:01 PM
sounds like a stitch up mate :(

give us he´s address, and we´ll send the heavy´s over to do his kneecaps ;)

TiGurr
09-14-2008, 11:42 AM
Right, the block's flatness is just on the limit.

Modern gaskets can withstand approx 1 thou of deviation per cylinder along the block. So, for example a 3 cylinder can have 3 thou, a 4 cylinder 4 thou and a 6 cylinder 6 thou. A v6 is treated as a 3 cylinder on each side, so its 3 thou. These figures are for the length of the block front to rear and diagonally across ther block front to rear, measured with a straight edge and feeler gauge.
Across the block (inlet to exhaust) the limit is 2 thou.

Well, my measurements are:

Length of block = 2 thou
Diagonal = 2.5 thou
Across block = 1.5 to 2 thou.

The worst reading is the cross block measurement at the rear of cylinder 4. Cylinder 4 is the one that blew the head gasket, so I'm hoping that a new (straight) head will seal it up.
I've ordered some M10 x 100mm cap head bolts to replace the head bolts. These will be torqued up to 46 lbft. Hopefully these will seal better than the stretch bolts. This is a technique used by Metric Mechanic for their performance builds.

b.u.ti-ful
09-14-2008, 04:33 PM
Sounds like you are taking as much care as possible - good luck and let us know how it runs.

dave45056
09-14-2008, 05:15 PM
If you buy the M10x100 cap bolts be aware that they are 5mm longer than stock strech bolts. So make sure the holes in the block are very clean. And run a tap down the hole a few times to make sure your torque is accurate. I'd recommend threading in all the bolts on the bare block and measuring the distance from the top of the block to the underside of the bolt head just to make sure.
Buy 12.4 grade bolts. These can be torqued to 64 lb-ft, and I'd recommend going to that number in 3-4 steps. And buy new washers for the bolts (standard part shown on realoem.com). They are cheap.

TiGurr
09-14-2008, 09:46 PM
If you buy the M10x100 cap bolts be aware that they are 5mm longer than stock strech bolts. So make sure the holes in the block are very clean. And run a tap down the hole a few times to make sure your torque is accurate. I'd recommend threading in all the bolts on the bare block and measuring the distance from the top of the block to the underside of the bolt head just to make sure.
Buy 12.4 grade bolts. These can be torqued to 64 lb-ft, and I'd recommend going to that number in 3-4 steps. And buy new washers for the bolts (standard part shown on realoem.com). They are cheap.

Yep, thanks Dave. I had that all planned.
Don't want the bolts bottoming out. If necessarry I'll grind a little off the bottom of the bolts if they're too long. I'm estimating 1.6mm for a crushed gasket. Is this about right?

I just noticed my typo.... 46 instead of 64 lbft! Luckily I have it written right in my build notes. Thanks for reminding me though :)

Just been looking at the Ra surface finish values. I'm aiming for 50 to 60 for a Reinz gasket, which correlates to 100 to 120 grit emery cloth to clean up the block face using a machinists straight edge to keep it all flat. I'm glad to say it cleaned up beautifully (after plugging the deck holes and sealing around the pistons with a bead of silicone) :biggrin:

dave45056
09-15-2008, 01:37 PM
Sounds great. Good Luck, It should work great. I did the same thing when I did my HG on my M42 engine thanks to the same Metric Mechanic article.
Sounds like you are on your way to having a good running engine. By the way, do you have a cam lock tool, flywheel lock pin and rigid chain tensioner to time the valvetrain?

TiGurr
09-15-2008, 05:54 PM
No, I don't have any of those tools. Rather than buying them I was going to use a DTI to measure TDC on piston 1, then install the head and align the cams using a vernier gauge to ensure they are parallel, and a set square to ensure they are perpendicular to the head face. Once this is all measured up I'll offer up the cam sprockets (which I fastened the chain to in 3 places on each one so it didn't jump teeth) and then bolt them up.

Unless anyone has any tools I can borrow ;)

TiGurr
09-30-2008, 07:26 PM
Right, the job is all done, plus a full service too. Drives great.

The head went on fine and the 12.9 bolts took some torquing to get to 64 lbft! I did it in 10 lbft stages up to 60, then the final 4. It was a bit nerve wracking as the bolts seemed to be stretching.

The hardest part was fitting the exhaust manifold back on as it was still connected to the rest of the exhaust system. Other than that it all went fine.

So at a total cost of £755 (including a reconditioned head, new thermostat, water pump & full service) its not too bad. Much less than a dealer would have charged.

b.u.ti-ful
09-30-2008, 07:39 PM
Thanks for following up and helping the archive with a conclusion indicating your methods were successful.