Assessing an unknown engine

[RobFrost]

The case itself reacted differently to the iridite.



I don't know if the alloy is slightly different but either way it definitely changed by the process.



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[sladey]

Impressive work

[911hillclimber]

Been busy then Rob!

Get it built before the cold comes in hard, thinking of the case sealant etc.

[RobFrost]

Matt grey high temperature coating seems closest to the original factory look.



Oh yeah I got a kg or so of steel parts zinc passivated.



In spite of some pitting from previous corrosion I think it's gonna be okay, very nice in fact.



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[911hillclimber]

It all needs to be the same colour for the castings and I think that could be tricky to do, mostly why I leave all the engine parts to mature by nature and leave well alone!

[RobFrost]

It all needs to be the same colour for the castings and I think that could be tricky to do, mostly why I leave all the engine parts to mature by nature and leave well alone!

How's the Lola Graham? All fixed up ready for next season now?

[RobFrost]

Last night I bagged up all the parts and tools I needed for an afternoon off work visiting the machine shop in Hinckley. Sadly today they called and cancelled, with a puncture the reason given.

So I settled for a little job reassembling the fan. I waxed in-between the metals to prevent moisture ingress and inhibit any galvanic corrosion.



First aluminium rivet going in - faithful to the original.





Followed by the others.



And all done.



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[RobFrost]

Today, armed with a couple of bronze blanks and my little drawing I finally made it to the machine shop in Hinckley. It's a good little place, a lathe, a mill, welding kit, a couple of bike lifts and some other stuff. By early afternoon there was a little congregation of men tinkering with their mechanical items, including a non-ddk 912 owner welding a rear bumper.

With only two blanks in hand, and two oversize valve guides to make, to a tolerance of .01mm, there was little room for error.

It turned out to be a wise precaution to turn the larger one first, as I had soon cut it a couple of hundredths of a mm too small. But I was able to use it to make the smaller one instead. It turned out the DRO on the lathe was only good to within about 5 hundredths of a mm so I relied upon many small cuts, a micrometer, and polished the final thousandths down with 3000 grit abrasive paper.

Four hours after arriving, both were done.





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[911hillclimber]

Good going Rob.
You need a good lathe to hold these fine cuts and a keen tool to cut rather than rub the surface.

Final assembly soon!

[RobFrost]

Another day back at the machine shop, milling out the old valve seats.








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[neilbardsley]

I assume that Bob had on some metal music in the background?

How do you set the angle in that machine and can't you put a tool in and tap them out from the other side?

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[RobFrost]

I assume that Bob had on some metal music in the background?

How do you set the angle in that machine and can't you put a tool in and tap them out from the other side?

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Yes there was metal blaring out turned up to 11 but it was inaudible due to the shot blasting cabinet.

You can't get the seats out without milling them because the interference fit is extremely tight. They have to be frozen and the head heated to 200°C before being driven in hard. To remove, you mill them out to within 0.2mm of the edge at which point they suddenly crack and come loose.

To set the angle, the main part is to use a cam box as a jig for the heads. That gets the valve stems vertical. On a couple I had to tilt the mill about two degrees, because the studs sticking out of the heads prevented it sitting dead flat on the mill base.



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[RobFrost]

It was with great trepidation I remeasured the custom turned oversize valve guides I made at the weekend, and remeasured the head bores. Dead on 0.06mm interference on one and 0.05mm on the other. Hallelujah!

It seems like an age ago I was putting the other guides in. I lubed them up, sat the head on a rubber mat and smashed them in with my home made drift.



I didn't ream them on the lathe, because I didn't know how precise the lathe was and the slightest offset on the live head would have yielded a guide too big for the valve stem. So I reamed them in the head by hand and honed.



Feeling very satisfied at having solved this little problem. Hopefully my happiness does not prove to be ill-founded.



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[PeterK]

Super impressed and feeling slightly guilty (but I’ll get over it in time) that I had my heads done for me.

That said, my exhaust studs had previously been replaced at a very jaunty angle, requiring drilling, welding in new aluminium, correctly drilling & tapping. I have the honour (?) of having had the worst set of heads the engineering shop had ever seen. My guides, etc were done at the same time.

[RobFrost]

I was back at The Machine Shop in Hinckley on Saturday. This time, an easy alternative to piston oil squirters to keep temperatures down in the engine. Suggested by Mike Bainbridge, notching the con rods allows oil which has lubricated the big ends to make its way on to the undersides of the pistons.



Six con rods notched both sides, a 1.5mm v shape. This is a strong part of the con rod not prone to failure so apparently doesn't create any weaknesses.



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