Skimmed Big Valve TC Head; can it be used?

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Spider 1969
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Skimmed Big Valve TC Head; can it be used?

Post by Spider 1969 » Sat Jun 04, 2016 11:24 pm

Guy,

I found an 1800 engine with a 105TC head. Took the head off, disassembled it (cam boxes had already been removed), solvent cleaned it, hot water cleaned it in an industrial washer and finally bead blasted it.

Bloke I bought it from already said it had been skimmed but as he was running standard cam pulleys and timing marks I figured it could not be that much. Turns out that 1 mm has been removed presuming that all TC heads have the same height (Seems logical and I've measured two others which were the same).
Also some crude porting and valve guide shortening has been done.

Questions:
Inlet seat has been affected (see attached photo):
- Can it be used or has the seat become too thin?
- Will it be possible to do full GC race style seat and valve modifications? If not will new seats make this possible?
Valve to piston clearance has been decreased:
- Am I right that if needed piston valve reliefs can be adjusted when using high lift cams ?

Appreciate your thoughts on this matter.

Sincerely,

Charles
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Guy Croft
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Re: Skimmed Big Valve TC Head; can it be used?

Post by Guy Croft » Sun Jun 05, 2016 2:48 pm

fantastic photos Charles, wish I could take them as good.

No problem with any of the things you want to do but I strongly recommend you press those shaved cast-iron guides out and fit some GC ones. When you shave the guide like that (yes I did do 20 years ago..) it can be impossible to do precision seat grinding. Yes a Serdi with solid pilot can cope but not my Serdi grinder with its uber-accurate taper-lock pilots nor Neway cutters with solid or expanding ones.

Moreover the shape that result from shaving the guides means loss of support for the valve on part of the radius and this can cause the brittle upper part of the guide *where the stem seal fits) to crack.

Just be careful with machining the piston valve reliefs (VRs) - the head is already closer to the pistons - you need to retain 4mm thickness in the VR region. Machining so much off the head *very silly thing to do..) will also have reduced the radial valve-piston clearance, because the valves are inclined not vertical.

I would advise you to use GC forged pistons, they can cope with any valve size and cam type.

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Spider 1969
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Re: Skimmed Big Valve TC Head; can it be used?

Post by Spider 1969 » Sun Jun 05, 2016 3:23 pm

Hi Guy,

Glad you like the photo's; actually I took them with my iPhone!

I have a nice GC head in my car and I consider this head a side project and an opportunity to develop my skills in porting and seat ops coming winter season (I try to keep summer for driving and winter for engine fettling). So nice to hear the head is useable. I now have to figure out which tools I need.

I will definitely use your trojan guides GC cams. As for pistons: depending on the chamber volume I will decide whether to build a new engine with GC pistons or to install the head on the engine in my car which already has GC A8 pistons. We'll be in touch after summer on this.

Thanks for your advice.

Sincerely,

Charles
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Re: Skimmed Big Valve TC Head; can it be used?

Post by Guy Croft » Sun Jun 05, 2016 3:45 pm

Get yourself some Neway cutters, they are good, I used them for years..

45/20 deg combo (or 45/30), 70 throat. for the inlet seats. A smaller diameter 15 x 45 deg for the ex. Solid pilots not expanding, 8mm and 7.8 (or 7.9mm) the size depends on the bore diameter which of course depends on the valve stem diameter, valves should just fall under their own weight after honing, 8mm may be too tight.

You'll need two valve-guide Flex-Hones (180 and 240 grade) but I will send info when needed.

Those 130/105/VX heads do not need a huge amount of work. Some smoothing on inlet side and short-radius correction. On the ex side mainly enlargement on the sides of the port near the valve guide boss, reduction of boss height and smoothing at 180 grade. You could go 220 grade but to honest that is more cosmetic than functional. I know as well as anyone else that somebody who buys a GC prepped head expects it to look gorgeous and 180 grade can look a bit ragged! Cosmetics do matter to people. I say that from a professional perspective.

As for fitting guides, you'll need a press tool. Not something I sell to be honest, though I do sell stem-seal fitting tools.

G
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Re: Skimmed Big Valve TC Head; can it be used?

Post by Piotrek125p » Mon Jun 06, 2016 9:14 am

I thought before that "skimmed" valve seat is unacceptable and should be lowered by grinding or cutting.
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Re: Skimmed Big Valve TC Head; can it be used?

Post by Guy Croft » Mon Jun 06, 2016 1:54 pm

it's not a problem to recut or regrind it,

G
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Re: Skimmed Big Valve TC Head; can it be used?

Post by Piotrek125p » Mon Jun 06, 2016 4:32 pm

Yes, I know, this is a common problem with TC head, but lot of folk use heads with "skimmed" seats and take for it a lot of money.
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