Assessing an unknown engine

[RobFrost]

I found half an hour's worth of midnight oil to burn measuring valves yesterday evening.





All may yet be discarded, depending on measurements, so I haven't cleaned them up fully.

This one's looking a bit funny. I'm guessing it either got a bit hot or the guide has opened up so much to allow the exhaust gases to creep up inside the guide.



Something for the weekend.



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[911hillclimber]

Yes, a bit of a gap to allow the ingress of carbon deposit to creep up.
All new valves are expensive!

[Gary71]

All new valves are expensive!

Yup. I went all in with new springs as well.
I’m still recovering now…

[RobFrost]

I finished measuring up tonight. I read it's the exhaust valves that always need replacing because they wear twice as fast.

All the exhaust valves are bigger than the minimum wear spec of 8.928mm, albeit only just above.

Whereas all but one of the intake valves are worn outside the wear spec of 8.948mm.

However I fully expect that when the guide wear is factored in too, they'll all be outside if the play spec.

One option I'm considering is to knurl and burnish the guides to suit the valves. But some of the guides are visibly out of round so I'm pretty certain they'll need replacing. They could still be reamed to suit the valves.

I'll measure the guides at the weekend before making any decision.





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[911hillclimber]

I think the engine rebuild kits from Design 911 also have new guides, but you need to check that Rob.

Fresh guide bores may well close things up enough to have a reasonable clearance.

[Gary71]

Once new guides are pressed in they normally reamed to size to suit the new valves as they may close up as they are fitted.

[911hillclimber]

Indeed, that is why I though the guide being 'shrunk' when pressed in the head might nip-up the wear on the valve shafts.

MORE head work, the most complex bit of the old 911 engine I think.

[RobFrost]

I think the engine rebuild kits from Design 911 also have new guides, but you need to check that Rob.

Fresh guide bores may well close things up enough to have a reasonable clearance.

Thanks for the suggestion Graham. Sadly it doesn't look like they do the kit for this engine, only the later ones. I do fully expect guide replacement will become inevitable as soon as I measure the guides but you never know, let's see.

[RobFrost]

In preparation for removing the exhaust studs, I was watching a couple of videos as you do, when I saw one of these contraptions.



It turns out I have a couple in a lovely old Britool tool set. I'd been wondering what they were. It took the first stud out no problems. But I wasn't feeling quite so pleased with myself after the second one.



All in all about six played nicely, four were a pain in the ass and that left two which were very very naughty indeed.

This one was flush so I welded it to a washer.





And welded a nut on top.



It took a lot of torque but ultimately sheared off.



In fact it was a lesson in perseverance- four attempts before it came free.



And the next one sheared too.



But came away second time

The aluminium cleaned up perfectly, no damage. That's all the exhaust studs out. So I can get the flanges faced if I want to now.

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[Gary71]

Good recovery I can see the struggle in the pics!

[impmad2000]

Well done , I ended up drilling most of mine out !

[RobFrost]

The magnesium stacks and throttle bodies have blooms of corrosion in all the nooks and crannies, including inside.



It would have been a lot of work to abrade it all off so I tried using some ferric chloride to turn it into something soluble.



I knew the reaction would be pretty quick and I had to keep the acid off any bare magnesium. A minute or two and the corrosion was turned into soluble chloride, and I neutralised everything in a bath of water.

Coating the magnesium is still something of a riddle. Sophisticated aerospace coatings will work, but no doubt be costly and require everything stripped to scratch.

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[RobFrost]

Having measured the guides and found one or two substantially out of spec, as large as 9.2mm in some places, I decided if I was replacing one, then I was replacing them all.

I already decided the job can be done to a high standard in a garage with basic tools. So given a) I'll be tooling up to do one, b) guides cost next to nothing, and c) it may bring some of the exhaust valves back to the top of their play spec, it was pointless to waste my time accurately measuring them all.

To drive them out you have to mill the end flush so it doesn't mushroom out when you're driving the guide out.

Not having a mill, I formed the strategy of buying an 8mm counterbore end mill, which would self-locate within the guide.



All I needed to do, was go slowly as the mill approached the head and keep the angle perpendicular to the spring seat. The aim is to not scratch the spring seat, although a tiny scratch would not matter since the shims and steel spring seat sit on top.

With a little cutting oil, the bronze cut really nicely and with a bit of care and taking time, it proved a highly satisfying job to do.



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[RobFrost]

Supplies arrived for the next chapter. Awaiting a 9mm/12mm sleeve.



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[Gary71]

Seeing that reminds me I have a Flexhone suitable for 84mm cylinders if you want to borrow it?