[ROVERNET - UK] 3500s head compatibility
kkinard at swbell.net
Sat Feb 18 17:24:28 GMT 2006
peter king wrote:
> I'm using an SD1 block. What is the benefit of the newer type heads?
All NAS SD1 heads were certified for use with unleaded fuel. There is
some debate as to how well the NAS SD1 heads hold up to this. I
personally think they did just fine. I have seen worn valves but never
any seat erosion on NAS SD1's. All '82 and later heads have hardened
seats...a real advantage if you plan to put very many (more than 20K)
miles on the engine.
All '76 and later heads use slightly larger valves. Not really much of
an advantange unless you bore and sleeve to use 3.702" pistons. If you
are going to buy new pistons, consider going to the larger bore. If you
do so, do not use Rover 3.9 sleeves. There are after market sleeves
that are thinner and will maintain cylinder wall integrity better than
factory 3.9 sleeves.
Measure the bores for ovality at the bottom and wear at the top. If the
bores have wear or ovality problems, you will most likely have to
replace the pistons and sleeves anyway.
Sonic test the block for core shift and the main caps for fretting. If
the water jackets are reasonably uniform and the main cap register
surface is tight, you might as well go for the bigger bores.
The increase in bore size is the single biggest improvement you can make
in engine performance for an every day street engine and you are MUCH
better off starting with a 3.5 block, either early or late, than you
would be investing in a factory 3.9, used or new. I will never again
buy a 3.9 for any reason. I would only buy a 4.0 if I knew the vehicle
and it's service history from new and intended to fit "top hat" sleeves.
All '76 and later heads use longer reach plugs which maintain a more
even opperating temperature because of their increased contact with the
One possible disadvantage: Early dual valve springs and their retainers
are stronger and can be revved a little higher. You cannot use early
springs on '76 and later heads.
I'd write my own book, but all this stuff has been said before. I'm
basicly an historian with lots of books, old parts, and a little hands
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