mopar wrote: ↑Wed Jan 20, 2021 5:36 pm
Got them out now the next thing to do is clean the block surface
Prior to reassembly, completely clear all the head bolt holes of any residual oil or debris. I like to confirm that a head bolt will easily thread all the way in by hand to each hole when I am done. It is common on these engines to suffer cracked blocks and failed head gaskets due to folks over looking this step.
As you mention, clean the block surface to remove all residual gasket material and corrosion with a sharp scraper making sure to not score the surface at any of the sealing areas. It is good to check the block for flatness with a good straight edge, but I have yet to find a warped block needing milling. I like to finish up with a good scrub down using brake-clean or something similar to remove all oil or grease just prior to placing the gasket.
Drew wrote: ↑Thu Jan 21, 2021 6:59 pm
When I did mine, the block was true, but the head needed a skim. I don't recall anything standing proud from the head, and I was able to leave the alignment parts in the block in situ. Lowering the rebuilt head has to be done gently and accurately to avoid those alignment parts scoring the newly machined head!
IIRC the rearmost head bolts need to be loosely in the head when refitting as the scuttle / firewall gets in the way once the head is in place
Nice work on the iron maiden!
After a skim, has anyone worried too much about timing? I.e. fitting an adjustable cam sprocket?
IIRC, BMW specified the head thickness at 129mm and allowed up to 0.5mm of material removed before the cam timing dropped out of spec.
My thought is that if the total machine work on the head and block combined is less than 0.5mm (0.019"), we should be in spec. Of course this is all assuming that the block has not been previously decked.
It would be interesting to obtain the cam specifications for the "7" cam that M90s were equipped with. This information would be useful to those with heavily milled heads.
The Iron Maiden has been tested and after some fine tuning it dit the job, so the cam is out (good advise RT(F)M more than once)
Rockers are out so I can test the valves.
I had a leak in cilinder 1, the inlet valve die not close, I thought it was some dirt from the disasembly, but after cleaning the valves intake nr 1 is not closing, it remains open about 5mm without springs. The valve is bent.
I lapped all the other valves with succes.
So I need to replace one intake valve for my M90