Assessing an unknown engine

[RobFrost]

I don't think this clamp was perfect for these particular cylinder heads but it looks like it'll get the job done.



What struck me on this first exhaust valve was just how tight and smooth it was coming out. I was expecting some corrosion and/or pitting. Let's see if the others are the same.



The jury's out on the valve seat. I gave it a wipe with some isopropyl alcohol. No problems obvious yet but I'll know more after a proper clean.



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[911hillclimber]

I used to use one of those compressors, so awkward esp when re-assy of the collet halves.
Use my motorcycle cheapie off ebay since (last 2 re-builds) and so much better, lighter and slimmer.

As to the seats:
I would not wright-off the seats until clean, clean the respective valves and do a simple lap job on them. Fill the chamber with thinners and see if they leak.
If not shine a high intensity torch down the ports in a dark garage and look for any light breaking through.
Use the lightest of valve springs to give things a chance.

If you change the valve guides, then things might change.

[RobFrost]

I used to use one of those compressors, so awkward esp when re-assy of the collet halves.
Use my motorcycle cheapie off ebay since (last 2 re-builds) and so much better, lighter and slimmer.

As to the seats:
I would not wright-off the seats until clean, clean the respective valves and do a simple lap job on them. Fill the chamber with thinners and see if they leak.
If not shine a high intensity torch down the ports in a dark garage and look for any light breaking through.
Use the lightest of valve springs to give things a chance.

If you change the valve guides, then things might change.

I have noticed since, the valve is seating on two thirds or more of the angle of the valve seat. In a good video online it said cut the seat so only one third makes contact. Not sure how critical that is. A thinner contact gives higher pressure between the valve and seat, which is likely to seal better.

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[911hillclimber]

Yes, that is true, but need good clean contact of valve and seat to see where things sit.
You can see where head prep takes so much time effort and money as you dig deeper.
You need all this lot set correctly to shim each valve spring seat…possibly.

I had to re shim my 3.2 in several places to get pre tension right.

All good fun!

[RobFrost]

Evidence continues to point to the engine having recently been rebuilt before it failed. One or two of the valves look like they might be new.





And some of the springs.





I got all the heads fully disassembled this morning. My teenage daughter helped do one valve. She said it wasn't "excessively unpleasant" which I'm taking as a win.

The exhaust ports were pretty coked up.



Tricky to capture in a photo but there's a clear ridge around the intake port where it approaches the valve.

And another bulge where the seat meets the aluminium.




As every good physicist knows, a flow will stick to a convex curve, provided the curve is smooth, due to the Coanda effect. This will draw gas into the valve, fully utilising the sharp part of the bend, freeing the space above for more flow.




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[RobFrost]

Sorry the photos are poor but I polished off the ridges making the curve constantly smooth.



And the same where the seat meets the aluminium.



That took the entire day.

There's some nice aerodynamics inside the ports guiding air around the valve stems which I didn't want to tamper with but I gently eased off some of the corners to reduce unnecessary turbulence.

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[RobFrost]

Here's where I eased off the corners.



I seated a valve to confirm the contact area is bigger than spec.



The intake studs look great.



But predictably the exhaust valves could be better. I forged a plan to take them out. Needless to say the studs had another idea. After heat, penetrating oil, impact driver, they were firmly in place.



The trusty solution, which has never failed me (yet) is welding a nut on. But it's a gamble, given these studs are actually usable and I could easily end up with something not so.

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[Nine One One]

Rob,
Have you tried any of that FREEZE OFF penetrating oil at all? Normally works quite well, and for the price might be an idea before you weld your nuts together?

There are others on the market, but Eurocarparts sells this stuff.........

https://www.eurocarparts.com/p/normfest ... or28944421

[RobFrost]

I pulled this ancient protractor from the depths of my measuring/marking drawer. Upon spotting my name scruffily scratched into the surface, I reflected how I was just a boy when I etched it there with my compass. The compass was part of a set my dad got me for my birthday and one of my most treasured possessions at the time.

A lot of water has passed under the bridge, and I've owned and held a lot of treasures since then. I wonder how that little boy would have felt to learn where life took me.

With it, I set the angle square to 30 degrees to help me make a seat cutter.




The MFI stacks could do with a little clean.





So I gave them a little hone inside.



And carefully cleaned up some of the mating faces with a razor blade.

They tapered down from 38mm to 35mm, where the throttle body suddenly jumps back out to 38mm. I took the executive decision it'll flow better if instead of a sudden step, it eases back out to 38mm over the last 5-10mm.




Next I polished the exhaust ports, and the inlets focusing especially on the critical areas around the valve openings where flow is the fastest.




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[RobFrost]

Rob,
Have you tried any of that FREEZE OFF penetrating oil at all? Normally works quite well, and for the price might be an idea before you weld your nuts together?

There are others on the market, but Eurocarparts sells this stuff.........

https://www.eurocarparts.com/p/normfest ... or28944421

Thanks I might give that a try... if I have the patience to wait for it to turn up.

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[Bruce M]

Aluminium expands more than steel when hot. You need to heat the head at least 60 degrees around the stud. Hot air gun works well if you are patient.
Or stick them on the BBQ like Alan Millyard does. I wouldn’t even try cold. Heat is applied first.

[RobFrost]

Aluminium expands more than steel when hot. You need to heat the head at least 60 degrees around the stud. Hot air gun works well if you are patient.
Or stick them on the BBQ like Alan Millyard does. I wouldn’t even try cold. Heat is applied first.

Funnily enough I had worked out the same thing. But I used a propane torch and nothing.

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[RobFrost]

I made a seat cutting tool for the 30 degree slope and picked a valve which was representative of the others.



In my garage sharpie serves for the blue stuff I've seen proper engineers use.






It cuts spot on, but if I cut here it'll only take a smidge before it's into the cylinder itself. Whereas I can cut the 60 degree side without too much worry.



I measured the 45 degree section on which the valve sits, at 1.65mm. I think spec is 1.25mm. I'll check that. I could do with it being a touch undersize before I seat the valves so it comes up to spec.

I'm tempted to take the smidge that's available from the 30 degree section. I'd rather the opening was wider than smaller, as it'll flow marginally better.

I'll not do anything until I've checked the play in the stems versus spec. One certainly seemed to have a lot of play on a simple manual check, without cleaning them up first, but most were tight.

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[RobFrost]

Five of the head gasket faces are good.



One has some pitting where it was corroded at the gasket, so I guess they all need a quarter mm off.



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[RobFrost]

I realised I can cut the outer 30 degree and the inner 60 degree faces regardless of whether any valve guides will be replaced. Only the actual mating face grind, made with the valve itself, needs to be made in the final guide.









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