Cylinder head dimension

[bobbo]

Is there a reference dimension for the 1725 cylinder head, which would be used to indicate how much shaving could be done before increasing compression to high. I am in the throws of prepping a rebuild and will likely have the head shaved to ensure its flat. Don't want to go too far, and the head has likely already gone through this procedure before.
Bob

 

[Shannon Boal]

I do not know how thick the head was when new, but this spec was in auto machine shop reference books years ago. You may learn all you need to know by sanding with a long flat block and some 80 grit sandpaper...., or the head can be checked for flatness with a machinist's straightedge and feeler gauges: the type of head gasket used here will work fine if flat within 0.004". I do not believe that you should "machine it to be sure it is flat". (Machining this way affects the valve train geometry, and makes the head thin....nobody is making new heads.) However, if you decide to have it done, a qualified operator on state of the art machinery can clean up the surface with very little metal wasted.

 

[Alpine 1789]

The head has circular wear indicators cast into it that should answer your question. I know there are multiple photo on this site somewhere, but I just pulled this photo from the web to show you where they are.

You can see the indicators on the upper edge of this head. Ideally, you might not want to invest too much in skimming a head that will take it right down to the indicators, since that will mean the head can not be skimmed again.

 

[bobbo]

Great photo. I think this is exactly what I needed. I'll check those on my head once off.
Thanks.

 

[alpine_64]

As a side note another good indicator of what you have is the depth of the metal between the head face and the side cover holes... When the heads are skimmed very heavily they can get very close to the face... Or even cut through.

You can skim a rootes head beyond the wear bars, but you need to open up the chambers to drop compression ( vizard mod will do this and add performance) however as mentioned you need to consider the valve train geometry.. You may need to get different length pushrods if its extreme

 

[RootesRooter]

If you go to or beyond the wear bars, you'll be encroaching on the threads for the side chamber cover bolts. I've broken a chunk off the head around the threads of one hole that way. If the head is otherwise stock, significant shaving will also raise your compression ratio enough to have to run premium gas.

But really, unless your head is damaged, 10 thou is all you'll want to have the head skimmed to assure its flat.

 

[Shannon Boal]

Is there a reference dimension for the 1725 cylinder head, which would be used to indicate how much shaving could be done before increasing compression too high.
I have searched every reference I have, no spec found for thickness, sorry. You can measure what you have, look at the casting where the side cover attaches to see if it is symetrical.....guess that it was an even fraction of an inch when it was made.....I do not know.

 

[bobbo]

Just want to ensure it is flat. So I wont be going too far. As suggested, A straight edge and feeler guage may be all that is required, and a light old school clean-up.

 

[puff4]

I don't know that I've ever found the original dimension for the height of a stock AM3 head for the alpine, but Tom H very accurately measured a virgin head a while back and got 39.2 cc. If you compare your current volume with the original volume (which resulted in the stock 9.2:1 compression ratio), you'll have some idea as to where you are.

For me, even my replacement head was skimmed pretty significantly, so I had to do the Vizard mod to bring the head back to nearly the exact original compression ratio. I will say that after that mod as well as porting, trimming the guides, doing 3-angle valves and matching the intake ports, it does run like a banshee, and even more so with Jerome's Weber setup and a distributor re-curve by Jim at Advanced Distributors. I kept the stock cam and it's an otherwise stock motor (apart from better seals)... I'm very happy with the results.

Here's an Excel spreadsheet you can use to calculate your compression ratio, if it helps. It includes original reference data as well.

https://drive.google.com/file/d/1mF_Ifq9wNK7dYJvDbn4CV54rpa1NbAFH/view?usp=sharing

 

[Knightowl61]

An option I'm looking into for a head at the end of the skim marks is a thick gasket.
Cometic makes a lot of different thicknesses and the link below says it's for the 1725 Alpine, but other browsers say Ford.

Cometic C5515-066 .066in MLS-5 HEAD GASKET | eBay

Anyone used thick head gaskets?

 

[Shannon Boal]

If you can get a thicker gasket, it sounds like a good idea to me: it should get the valve train close to original angles. I have no source for custom head gaskets, but, I think they are made from dead-soft copper. In 1974, I modified a Cheyy 427 L-88 to run on pump gas.... I stacked two head gaskets. Worked fine, the Corvette owner said it had never run that well. Did that in the eighties with a VW Diesel using an oddball long stroke crank, no problem there, either. I don't do much anymore, but I got some stories...

 

[Tim R]

A company in the UK called Gosnay's Engineering are pioneers in making stainless steel shims to restore 'meat' to cylinder heads that have been repeatedly ground and as a result have too high compression. The normally do Rovers and their initial charge to make a template for the Alpine head is quite high but subsequent shims would be cheap. At one point the UK owners club was looking at the possibility of getting a template made but I think the decision was that at the moment it is not critical as plenty of heads are around. Some people have fitted either two solid copper head gaskets or an extra thick one to achieve the same result. The other thing to remember when looking at heads and compression is that sometimes the block gets skimmed too which can throw all those calculations out.
Tim R

 

[bernd_st]

Kevin,

what are those light blue valve stem oil seals?

 

[puff4]

Kevin,

what are those light blue valve stem oil seals?

Those are Precision Race Components Viton (FKM) valve seals, sourced through EOK, Bern. You need the OD of your valve (probably 8mm) and the OD of your guide to get the right ones. The guides need to be cut-down to make them fit, so that has to be done prior to guide installation. Here's a website, narrowed down to the basic sizes:

http://usseal-eok.com/seals-by-size.html?material=9&style=4&style_type=35

As with most things in my work restoring cars (and lots of other stuff), I try to modernize under-the-covers to create a better build standard wherever possible, while leaving the outward appearance to be bone stock (as much as possible) to preserve the original look.

The original factory o-rings in the stem cap work pretty well... for a while... until they harden. Once hardened - and that doesn't take long - they no longer offer protection from oil loss, so you'll start burning oil through your valve stems - a common complaint. As a result, the backs of your valves will start to load up with carbon deposits, impacting gas flow and thereby reducing your overall performance. So, a more modern approach was needed, and these fit the bill nicely.

 

[bernd_st]

Extremely good stuff, thanks for your explanation. Hardening oil seals are indeed the culprit. Don't know how many brittle ones I have scratched out of the retainer grooves over the years. Nice and a great idea...

 

[Tom H]

Note that it takes about 0.014" shaving of the head to decrease combustion chamber volume by 1 cc. Furthermore, a 1 cc decrease in chamber volume will increase stock CR of 9.2:1 to 9.35:1.

Kevin, nice job publishing that spreadsheet !

Tom

 

[puff4]

Kevin, nice job publishing that spreadsheet !

Tom

Thanks, Tom. Glad it was helpful. But wasn’t that originally your spreadsheet?!

Hey, as for performance, Tom, having driven my Alpine you should be able to testify about its punch. (And it’s about 15-20% stronger than when you drove it, since it now has a new Weber setup and a nifty dizzy recurve!)

 

[Tom H]

Kevin, yes, that is my spreadsheet. But you cleaned it up and made it more usable and easily accessible.