New head studs ? Increasing compression ratio

mtb_tuli

mtb_tuli

Active Member
Hi,
Just sorting out all parts, that I will need to re-build my heads to the engine. I will give away my SD1 heads for skimming, but not really sure, what to skim to slightly increase CR. I plan to use tin type gaskets again.
At the moment I plan to reduce by 0,6 mm (20 thou inch is 0,508 mm) which should increase from 9,25 to around 10 :1. If anyone has experienced figures, it would help.
Then, for the older heads there are no "pre-stretch" bolts used, where you always must use new head studs.
Obviously, the old heads (no SD1) which I removed, were off some time ago, because all studs had no rust and were mounted with copper grease. The lower 4 ones were tighten like hell....
I´m not sure, I have read somewhere (manual ?), that you could use the studs 3-4 times, but i.e. RPI says, never ever use the old studs (ok, they sell new set for over 100 ;)).
Any help appreciated.
 
P5B/P6B/SD1 engines use bolts to hold the heads which can be reused without problems. The outer row of bolts only need to be lightly tightened as they were dispensed with on later engines.
 
Apparently the lower bolts were deleted as they contributed to headgasket sealing / uneven clamping and poor combustion causing oil to be contaminated and sludging / coking up engine internals .
Using correct oil / keeping it changed at least 2 times a year reduces the chances of sludging.
Took rover at least 25 years to find that out.
Clive.
 
I don't think you need to do anything more than what is standard fit for a 10,1 CR build.
The P6 engine at 10,5CR uses bolts, like Harvey says, so anything more than it came with is OTT in my mind.
 
Thanks for your help, guys.
No, I do not want to raise CR over 10, but I´m not sure, if 0,6 mm is a correct figure (should be "approx ok"), so if anyone had tried this, a figure would help.
 
If you want to ensure you can comfortably use regular 95 unleaded, you might want to take it no further than 9.75:1 or thereabouts of the later LR Discovery.
 
It´s ok to use 98 oct or the popular 100 oct fuel, the car will not get more than 5tkm per year I think, but who knows, I still have only the "ride of fear" from the Netherlands in my bones and originally only wanted to change a front screen seal...
The V8 Forum is interesting, but all the guys have mixed up components from all over the Rover generations. A P6B base and SD1 heads is definitely a combination, which these guys put in the pedal cars of their youngsters. But, I think I will try calculating it myself, let´s see, what happens. On saturday I took off the oil pan. Oioioioi, the bottom looked like the bottom of a river in the goldrush days, but you cry out, AAAALUMINIUUUM !
 
actually Rover new about the lower stud issue way back in the early Seventies. The Leyland P76 engine has them deleted but the bosses remain.
 
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