Assessing an unknown engine

[PeterK]

I’m enjoying your creativity (& braveness) Rob

[911hillclimber]

PhewI
That is a lot of hard work Rob, but you know I love the DIY approach.

First set-up is always the hardest, all the thinking time and building the confidence.

Soon be onto the next stage!

[sladey]

Nice work

[RobFrost]

Not being an engineer, some apprehension has been building with respect to machining the gasket faces of the remaining cylinder heads. The first went fine, but I doubted my ability to get them within the required tolerance of each other.

The tip of the cutting tool didn't move during the first one, but I thought it might, so I welded and ground the backstop behind the tip to hold it tighter.



Here it's sitting on the granite slab I'm using to measure the heights, next to one of the steel blocks I sit under the gasket face when measuring.



As I understand it the radial runout isn't as critical on this job, because the upstand around the gasket face is to protect the machined face when the heads are out of the engine. Here's setting up to minimise the axial runout.



And here's the runout dialled in to a hundredth of a mm: https://photos.app.goo.gl/aCv8o3fr6RCBQd4x8

After cutting the gasket face, on 1970 heads (not on earlier heads, I believe), you have to pull the cutting head back 2.6mm and take the exact same amount off the surrounding upstand.



The method i think a better engineer would use to get these coplanar, would be to have a larger aluminium jig in the lathe head, eliminate runout on that, then bolt the head flat to the jig. Doing that way ensures the two planes in top and bottom of the heads are parallel. My simpler method has been to set runout using the existing gasket face. That's fine, assuming they were true in the first place, which I measured them to be. Of course I'm compounding my inaccuracies with the inaccuracies of the engineer who went before me. But I'm standing on the shoulder of a giant here so to speak, they were so accurate before.



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[RobFrost]

The big uncertainty in the cutting process was that I had to rest the cutter gently against the face and hand-turn the lathe, adjusting to the exact point where it was cutting 0.00mm, but would cut 0.01mm if I advanced the carriage. Here, I would zero the DRO, put the cutter to the side, advance the carriage exactly 2.50mm and lock the carriage. There's probably a better way of doing this, but if there is, I don't know it.


If you remember this creation, it's the original sump plate made a touch taller to accommodate the 964 oil pump. Whilst at the machine shop, I availed myself of the oven to powder coat it.



After cutting and measuring the next three cylinder heads, it started to look like I might not be entirely incompetent. (Note one is having a 0.25mm thicker shim than the others.



Nobody was more relieved (or surprised) than I, that they were so close to each other. So I proceeded with great trepidation and care in the hope the good results would continue to the end of the day.

And sure enough I soon had six freshly faced cylinder heads looking up at me.



The task took all day, a large part of which was pulling the studs from each head and fitting studs short enough to go in the jig. But generally, going painstakingly slow and being careful over every step. I felt great driving home, knowing probably the most difficult part of the rebuild is in the bag.

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[neilbardsley]

Well done. Hopefully downhill from now on!

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[RobFrost]

With all six sealing faces cut, extra care is now required to not scratch them. To this end, I have taken to keeping them covered with masking tape when possible.

I had another oven session last weekend driving in the remaining valve guides.

It would have felt like a big watershed to finish this job, but one inlet valve seat went in a bit easier than the others. In fact with the head heated, it started to drop a couple of mm into the bore of its own accord. Once driven in, it was well and truly stuck in there but on reflection I decided not to take any chances and to machine it out and go again.

My suspicion was that this was the first head I bored, before I refined my technique, and it may have rocked in the vice a little, causing the bore to be slightly tapered. This would result in two further visits to the machine shop which I was able to squeeze in on evenings after work.

Having done the job before and now appreciating the degree of painstaking care required, I could now machine out the new guide with greater precision than before.



Subsequent measuring revealed this bore was indeed slightly tapered so I cut it again a little bigger and confirmed no taper. This required another new seat, this time half a mm wider, and another visit to cut that precisely to size on the lathe.



And finally this morning, it drove in nicely before going back in the oven for twenty minutes to stabilise.



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[RobFrost]

A spot of powder coating today.



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[RobFrost]

Time to cut the valve seats again, this time with shiny new seats. Three angles, 30, 45 and 60.





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[RobFrost]

Finally finished up the valve seats this weekend, cutting the exhaust seats to three angles.

30



60



And 45



Before putting all the studs back in.



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[911hillclimber]

Really good going Rob, you have fought it all out!
Assembly of the engine will seem a breeze after all this machining.

[RobFrost]

With the 1970 911 going off to paint, I have the luxury of some space in the garage and a chance to move this engine on.

The nose bearing removed from the engine looks mint (at least on the inside) and I suspect it was new when the engine blew. Recall, the engine had clearly failed after a rebuild as all six pistons were intact but I found fragments of a seventh piston inside the case.



So I measured it and 0.03mm is at the new end of spec.



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[RobFrost]

A minor fly in the ointment is a score mark around the nose of the crank. It's around 1mm wide and will sit somewhere under the nose oil seal. I'm going to leave it because being radial rather than axial, I think it will still seal, and thinning the crank would make it less likely to seal.



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[911hillclimber]

Dear me, a lot of work and stress Rob!

Started the read back when you re-cut the faces for the gaskets etc. Did you need to do them, or were they uneven/damaged?

When I did my valve seat grinds I used thinners to roughly check the seal (one valve spring used, then a good light which was the same diameter of the port(!)

Keep making gains while the body is away!

[RobFrost]

Dear me, a lot of work and stress Rob!

Started the read back when you re-cut the faces for the gaskets etc. Did you need to do them, or were they uneven/damaged?

When I did my valve seat grinds I used thinners to roughly check the seal (one valve spring used, then a good light which was the same diameter of the port(!)

Keep making gains while the body is away!

Plenty to do but no stress - I'm doing it for the pleasure of doing it. Some of the gasket faces were pitted with galvanic corrosion where they met the gasket - only 10th of a mm or so but it needed cleaning up. Thanks for the tip re the valve seals.