Assessing an unknown engine

[911hillclimber]

Dare I say Rob, the cylinder head place you know of in Warrington would have done the lot.
Welding was a major hurdle, great job fixing that.

[RobFrost]

Dare I say Rob, the cylinder head place you know of in Warrington would have done the lot.
Welding was a major hurdle, great job fixing that.

If I remember correctly, they didn't seem keen on doing the valve guides the way I wanted. A lot of places nowadays slide a sprung sleeve insert into the existing guide, but in my view this reduces the capacity of the guide to conduct heat away from the valve. The best possible job is a single, new piece of manganese bronze pressed in with the correct clearance to the valve and the correct tightness in the head.

I do now plan on using Headshop who you refer to, to reface the gasket face of the heads and I was always going to ask them to twin plug them. I may ask them to set the valve heights too, depending how those turn out. But I've bought all new valves so that may not be needed.

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[911hillclimber]

You may need to re-shim the spring buckets so the spring loading is right and equal, all depends on the amount of lapping etc that the engine may have seen.

I had to mess about on 3 valve to get the spring heights right and the shims are all a bit coarse, so tricky to find a compromise.
Dempsey book details this well.

That method of sleaving the valve guide ID sounds awful to me!

[Gary71]

I had new valves/guides and the seats recut so inevitably the spring heights needed work. I bought a selection of shims from Porsche and spent a joy filled day mixing and matching with the originals to get it right!



Satisfying to get it right, how much difference it makes in a normal road engine that tops out at 6500 is debatable.

[RobFrost]

That method of sleaving the valve guide ID sounds awful to me!

These are the liners they use. I'm pretty this is what Headshop do.
https://www.fondera.co.uk/classic-bronz ... uides.html

I'm sure it's very good but it wasn't for me.

[911hillclimber]

I presume the idea is to ream the existing (oval ish) guides out and push these in so that the edges come tight together and hence a tight interference fit. Ream again to valve stem tolerances.

Ref the spring height and shimming.
As Gary says, endless fun...

I was building for 9,000 rpm and very very expensive valve springs, so prob too cautious.

As I've said before, rebuilding the heads is the most time consuming (and boring) part of the flat 6 air cooled build.

[RobFrost]

I picked up the heads in the week, and some of the parts had arrived to make the jig for drilling the two bores myself.

I measured up the four studs on the cylinder head and drilled 8mm hols to slide over them, into a 4mm mild steel plate. I figured this thickness will be rigid enough to give me an accurate jig.





I deburred all the holes to make sure I don't marr the machined surface on top of the heads.



And some of the studs had a couple of threads showing, so I turned all the studs in until the threads were in the aluminium. I noticed on dismantling that some of the studs stuck out a bit high.

I have this steel rod, one end of which I polished down to 8.98mm for a snug fit in the valve guide.





This 15mm outside diameter sleeve fits over the top.

And then I'm going to slide one or two of these 15mm inside diameter sleeves over the top and weld it to the plate. This jig can then be bolted over the head with the damaged bores for me to run the 15mm drill through.



Slight error though, I bought aluminium outer sleeves which obviously won't weld to the jig so I have steel ones on order.

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[RobFrost]

While I wait for the correct sleeves I gave a final ream to the new, fitted, bronze guides on the heads that are ready.



It just took the tiniest amount off where they may have tightened as a result of being driven into their bores. Then I honed them.



And cleaned out and put away to one side.



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[RobFrost]

The bits I needed finally came, so I made a little progress this weekend. I'd been waiting for 14mm and 15mm inside diameter sleeves for this jig, which would form the guides for the drill.



I got the drill guides welded in place on the jig using a good head.



They were good and centred on the damaged head.



And I measured to make sure they were coming through central in the valve seat.



Once I was happy I drilled through the bores.



I've reamers on order to tidy up the bores.

Then I set about cutting the 45 degree angle in the seats with a more precise cutter than used for the 30 and 60 degree faces.



That all looked good and tidy to me.



But sadly, inserting the valves showed the seats have been cut too far. The valves seat right on their edge. They need to seat a few mm in from the valve edge in order to conduct heat away adequately.

That was a bit demoralising, because I don't think replacing the seats is a job within my capabilities. Most of it I can do, but it requires cutting the head to receive an oversize seat. The cutter alone is £500+ and I'd need a mill, as well as a specialist punch to drive the seat in, and a jig to hold the head to receive the necessary force at an angle.

Does anybody know the standard sizes of the seats? I can measure them to roughly 43mm x 36mm x 8mm and 48mm x 42mm x 8mm but I need precise measurements. With Porsche tax they're circa £400 a set of 12 whereas Serdi ones are around £6 each. But I can't find the precise measurements.

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[911hillclimber]

Mmmmm...
I think I would be taking that head to the Cylinder Head shop in Nantwich to sort it out?

[Bruce M]

The top cut narrows the seat to move it away from the valve edge but only if there is enough room for that top cut (can’t hit the outer edge of the seat) and it doesn’t narrow the seal less than spec.

[RobFrost]

The top cut narrows the seat to move it away from the valve edge but only if there is enough room for that top cut (can’t hit the outer edge of the seat) and it doesn’t narrow the seal less than spec.

Exactly that. The 30 degree face is already in contact with the cylinder head itself on a couple of exhaust valves so I'd be cutting aluminium. And if I did, once I flip them over, the valve would be standing up taller than spec anyway. They would work fine without new seats but I think I want new unless it proves impractical.

[RobFrost]

With the lack of updates one could be forgiven for thinking there has been no activity on the engine over the past couple of months. And indeed I have found a renewed energy for working on the bodywork so that has taken priority of late.

Nevertheless I have had a few experts performing various processes for me and found a few spare evenings to tinker things along.

Of the four spots I decided to weld on the mag case, this was one of the trickier ones.



This broken off bolt hole, previously welded nicely, I machined flat.



I chose a different type of plug for the oil bypass mod to the one I originally chose, and gently sculpted the case so the shoulder of the brass plug seated nicely. Fixed in with permanent loctite. Blocking off this hole prevents surplus oil being returned to the sump where it would have to be scavenged again. Instead it is directed straight to the scavenge side of the pump.



I got the correct piston for the bypass style oil pressure valve.



Another little area of welding on the case which was a touch too pitted for my liking.



And finally I reamed and honed the 6th cylinder head bores ready for the guides.



I remembered why it is important to ease off the corner of the bore. As you drive the guide in, it prevents tiny fragments of aluminium being broken off the corner and getting dragged in-between the bronze guide and the bore.

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[RobFrost]

I used a bolt to drive the steel threads into the mag case.



Had I paid closer attention I would have noticed on an insert done previously, that the nearby flange had been eased off to make room for the hesd of the bolt. You live and learn.



Various inserts - pretty sure I placed them in all the places recommended by Mike Bainbridge!









I was warned that I had no chance of getting all the studs in parallel without a mill. For that reason, I was especially careful with the jig I made and I think everything is as straight as if a pro with all the gear had done it.



Keeping any detritus out of the oil passages as I worked.



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[RobFrost]

Getting the alternator apart was quite a game, it was so jammed.

And this little guy was determined not to come out. But I got him in the end.



I left all the magnesium parts with a local media blaster for a couple of weeks and they came back looking pretty shiny.







And I found an aerospace company able to give them all the original chromate surface treatment. No finish will adhere properly, long-term, to magnesium. But with this process they will.


The chromium 6 used has a bad safety reputation so I washed everything thoroughly before handling just to be on the safe side.




This is the worst spot of pitting. I was undecided whether to fill it with something.




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