The V8 Owners Forum -

it's an 11A***** engine number , is it likely to have comp gaskets ( sd1 auto )

use the 9.35 pistons with tin gaskets should give you about 10:1 would be about ideal for a combined LPG petrol set up.
Mike

use the 9.35 pistons with tin gaskets should give you about 10:1 would be about ideal for a combined LPG petrol set up.
Mike

thankyou for that mike , i think he has offered it too the other bidders ..

i was just wondering ..as i say i have 8.13:1 pistons now
what if i just get the heads skimmed ?

..it would save money on gaskets

SD1 engine will not have comp gaskets standard, no 3.5 ever did. The only heads to use comp gaskets are 10 bolt heads. 4.0, 4.6 and the very last 3.9 engines are what these heads belong to. The last 3.9 ones are actually early heads with a bolt hole blocked of and skimmed by 1mm to make up for the thicker gasket.
Skimming 1mm of the older heads and using tin gaskets gives around .7 rise in CR assuming they haven't been skimmed before. To be honest there are other figures out there for this but I have always went with .7 as its the one I have seen the most tho never tested it for proof. Ontop of that you can take 40 thou off the block with 25 thou of the piston tops and that will give you another jump. Warning though in that you will probably have to machine pockets in the pistons or your valves have a good chance of hitting. As ever everything needs to be carefully measured to make sure as the rover engine was never the most accurately machined. You will also have to machine the inlet manifold as it will no longer fit the V.
Add all that together and your looking at a fair bit cash in machining so my advice is you would be better buying pistons. Safer if your not sure what your doing and cheaper even with new pistons. .75 pistons arent hard to get and if you wanted you could also skim heads, depending on cam this should all be safe.

kiwicar wrote:use the 9.35 pistons with tin gaskets should give you about 10:1 would be about ideal for a combined LPG petrol set up.
Mike

I thought that the stated CR of the pistons was with tin gaskets? ( I could be wrong here!)

When Rover went to comp gaskets they skimmed the heads to reduce the standard 36cc to something like 28cc to retain the same CR. (Or was that just for the 4.6 lumps?)

The tins are around 20 thou thick, the comps around 40 thou.

Someone suggested skimming 1mm of the heads to retain the same CR as tins, infact you would only need to skim 20 thou (0.5mm) off to retain the CR of the pistons whilst using comps.

V8 Dev told me that every 8 thou off the heads is worth a 1cc reduction in the combustion chamber vol, my measurements confirmed this.

You certainly could skim more off, mine have had 70 thou off to get my 9.35 CR 4.6 pistons up to 10:1.

The problem with the different head gaskets and skimming is that it will mess up your lifter preload. You need to aim for 20 thou. You can sort this out with shims under the rocker shaft pedestals but IMHO they are a bit crap! You can never get all of the lifters the same or anywhere near each other! The other problem with shims is that they mess up the valve train geometry which isn't all that good to start with even with a standard cam. Real Steel do adjustable pushrods which I think are "Crane". I still had to shorten mine by 4mm but I did have 1.5mm off the rocker pedestal bosses to sort out the bad valve train setup which made the pushrods in effect far too long.

The other thing with the pushrods is that they get very close to the heads in the pushrod holes at either end of each head. I filed out the holes in the direction required rather then drilling them out.

As to how much BHP you'll get out of raising the CR, well its never as much as you would hope for! Finger in the air, maybe 15- 20 BHP. There is a CR change calculator floating about on the web that will give you an idea of the increase. You may get more as you are using LPG as this likes a high CR.

By the way, if you are using 14 bolt heads don't fit the outer row of bolts at all, they are the reason that the heads blow into the valley area!

Do you ever get the feeling that doing one simple thing ends up being a 'can of worms' ?

HTH,

Pete

it looks like i may have just come across a set of 10.5:1 pistons

now what do i watch out for , do i need to shim the rocker pedestals , i have a set of shims here

with TIN head gaskets lets say .... ?

the engine number i have been given is

48105167b ??

bodger wrote:it looks like i may have just come across a set of 10.5:1 pistons ...complete engine actually

now what do i watch out for , do i need to shim the rocker pedestals , i have a set of shims here

with TIN head gaskets lets say .... ?

ps:
can i tell if the pistons are 10.5 .. do they have any dish at all in them ?

If you are dealing with these engines day in day out I dare say that you can tell what the CR will be just by looking at them. I think that all the pistons do have some dish in them.

I guess the 10.5 jobbies are quite old as it was only the earlier engine that used them.

If the engine is setup for tins and you go to comps the pedestal shims won't help, they'll make things worse! (They're really really ment for high lift cams). Of course if you use comps and skim the heads 20 thou the engine dimensions will remain the same so your preload won't change. (Of course that does not mean that it's right!) Your manifold should drop straight on.

Personally I would not consider using tins as they leaked on my old 3.5 engine, others may disagree. (It did have the outer bolts fitted though).

You should check the preload by dismantling each lifter and draining the oil out, you can then measure from the snap ring to the inner part of the lifter with a thin (0.5mm) thick piece of wire when the lobe is on the base circle. This is a pain in the arse and in my experiance is totally impossible with shims! (hence adjustables on my 4.6)

The only real 'proper' way to work out the CR is to burette at least one piston at TDC and the coresponding head chamber, you can use a bit of maths to work out the gasket vol. You can then work out the CR. I did all 8 cylinders on my 4.6, they do vary a bit but not too much!

Pete

i have just found another engine ... with 10.5:1 pistons

this one is with an auto box too ...

engine number 42526254C

i was wondering as chris mentioned about shims ...do i not need them to keep pistons WELL away from valves ...sorry to be a bit dense on this but i don't want make a mistake

Keith,

No need to worry about shims for clearance reasons, I would have some concern with using s/h pistons of that age though, they could be anything from 30 to 40 years old unless the motors had a complete rebuild with new pistons at some stage, then they could possibly be oversize if they were available.

It would be a good idea to check your existing cam and followers and be prepared to replace them if worn, I believe a 3.9 cam properly set up can yield some extra power without running into any clearance issues for a nice torque based motor.

Kevin.

thankyou Kevin , i was thinking about that but hey why not ...lol

the ones i have in there are 1982 ish era so whats 6 or 7 years

i'm won't be dragging up the strip and i can always have the old ones to put back in ..if the pistons are really badly scored then i wont use them

Keith.

The later rods are slightly stronger but for your use the early ones should be ok.

If the engine has been modded with a lightened flywheel, worth taking a close look to see if their are any other goodies.

If you going to strip it and the cam looks in good nick remember to number the lifters to the lobes so that they can go back the same position as they came out, presuming that they ok and it not something with too much overlap which wouldn't suit your application.

Kevin.

it comes with dissy , carbs , inlet manifold , heads , covers , SD1 exhaust manifolds and downpipes , clutch , flywheel , block & pistons , alternator , and i think front cover and water pump ...

so lots more bits to play with ..and find room in my cuboard for , theres always the bedroom i suppose ...lol

Keith,

Sounds good and I still have the hardware for an injection system on the kitchen table!

Kevin.