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JPSH120
United Kingdom
1178 Posts |
 Posted - 03 Dec 2010 : 21:42:01
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I have met people who have replaced the cylinder head on a holbay engine with a standard one, but does anyone know what is involved in doing so?
Is it a simple swap or are mods required??
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Edited by - JPSH120 on 03 Dec 2010 21:42:51 |
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UMU
United Kingdom
343 Posts |
Posted - 04 Dec 2010 : 10:40:37
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im pretty sure that the only difference between the two are the size of the manifold inlets, meaning that if your wanting to run stromburgs, your able to just swap to the standard one.
im thinking more and more about putting webbers on mine so want to find out what i need to do, but my mechanic doesnt think theres much involved
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1922
United Kingdom
549 Posts |
Posted - 04 Dec 2010 : 19:26:27
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The combustion chambers are a different shape.
The holbay one is bigger and heart shaped, the standard one ha s straight sides.
If you put a standard head on you will have a higher compression ratio and you might have problems with pinking.
The standard inlet manifold will fit the Holbay head, I've done it.
Unless the Holbay head is badly damaged why would you want replace it with a standard one? |
Edited by - 1922 on 04 Dec 2010 19:27:54 |
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1922
United Kingdom
549 Posts |
Posted - 04 Dec 2010 : 19:36:08
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Martin, you can fit webers to a standard head. The only problem is that the lower centre bolt for the inlet is in a slightly different place.
I have done this one too :-) but it was a long time ago. P
But it'll go better with a Holbay head or one that has had some had flowing etc and a higher lift cam. |
Edited by - 1922 on 04 Dec 2010 20:22:27 |
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1922
United Kingdom
549 Posts |
Posted - 04 Dec 2010 : 19:50:41
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Just read your other thread.
How damaged is your head?
It might be fixable, I've had badly corroded heads repaired in the past for couple of hundred quid. |
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JPSH120
United Kingdom
1178 Posts |
Posted - 04 Dec 2010 : 21:54:10
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The head that came off the car is knackered, internal waterways are corroded beyond repair.
I have another holbay head but I'm not sure of its condition, keeping my fingers crossed!
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UMU
United Kingdom
343 Posts |
Posted - 05 Dec 2010 : 18:46:51
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thanks for the advise
i have 2 spare heads, would you like to see them, one may be a holbay, but not sure.
theyre not in A1 cond, but am sure there worth a shot.
the one that i think may be a holbay one, had a holbay type rocker cover on it
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JPSH120
United Kingdom
1178 Posts |
Posted - 05 Dec 2010 : 20:54:21
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If you do have a spare holbay head then that would be great, just incase the one I have is no good.
I'll let you know once mine has been health checked.
Thanks.
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1922
United Kingdom
549 Posts |
Posted - 06 Dec 2010 : 18:49:26
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I thought some pictures of heads would help you identify what you have.
If the head is on the engine check for the serial number stamped on the top. If this was a Holbay head you would see a number where I have drawn the red box:
If the head is off the engine have a look at the underside - the combustion chamber shape will give it away.
This is a standard unmodified head 1725 allow head with straight sided combustion chambers. As fitted to the Rapier, Alpine, Humber Sceptre, Hunter GT and the posher Hunters:
A standard H120/Hunter GLS will look similar to this. This is a Holbay Marathon head with slightly larger than standard combustion chambers but still with the 'heart' shape chamber you should find on an H120/GLS head:
Lastly for comparison this the combustion chamber on my Coltec head. Note the enlarged chamber and bigger valves:
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Holbay120
United Kingdom
177 Posts |
Posted - 06 Dec 2010 : 21:43:47
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Thanks Derek, that's a big help to a lot of people and I am most certainly one of them! Cheers
Best Regards
David McKenna |
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UMU
United Kingdom
343 Posts |
Posted - 07 Dec 2010 : 20:37:33
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yeah thats brill to see the difference, thanks.
also it clarifies that my spare heads are NOT holbay, sorry
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1922
United Kingdom
549 Posts |
Posted - 08 Dec 2010 : 13:27:11
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Standard heads can be modified to Holbay specification by modifying the combustion chambers and fitting better quality valves and springs etc (my new Coltec 1922 head started life as a standard Rapier head).
It's not that much more work than having an old head refurbished and converted to run on unleaded.
So if your H120 head is in very poor condition it might be cheaper to have a standard head modified. This is something a your local local engine shop might be able to do, or give Richard at Coltec or Chris Draycott a call to find out what is possible (and how much it will cost!). |
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Topic |
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Standard head on Holbay engine.
