Engine cams and compression ratios

Paulcovy

Member
hi all started my v8 up on Saturday after noon only for it to cut out .... after removing the starter Motor and other things I deduced the engine had locked up ..... after removing the heads and sump I found that the big ends have picked up and locked the engine due to oil starvation .... so I'm gonna rebuild the motor ive done around 40 miles in the car since I bought it and the plan was always to rebuild it anyway so no biggie ... however if the engine is a 10.5 -1 compression ratio can I use the rebuild kit from a 9.35 -1 as the price seems very good for the kit ... the cam in mine is shot .... and a right mess ....
 
Rebuild kit doesn't have to match the compression ratio.

The compression ratio is decided by the pistons - so if you change them you'll change the compression ratio.

The type of headgaskets you use will also change the compression ratio. Composite ones will lower the compression ratio a little as later cars with this setup usually have smaller compression chambers in the heads.

A slightly lower compression ratio will enable you to run on standard unleaded rather than the super you'll be using now to avoid pinking.

If you're rebuilding you may want to also change the front crank seal to the neoprene type.

If you're taking the engine out it may be worth machining it to take the rear neoprene seal rather than the rope seal too.

Rich
 
Is that by changing the front cover to sd1 ? So changing to my this cam and composit gaskets will actually be beneficial to the engine
 
you can just change the seal rather than the whole cover... unless you happen to have a front cover and dizzy/oil pump gears lying around of course....
 
It's really your choice keep the 10.5:1 or go down to 9.9:1 using the later, composite gasket for the cylinder heads. With that you'll lose a few bhp but as Rockdemon says, you can use regular 95 octane. The advantage is supposedly better sealing but done correctly, the original, tin gasket should be perfectly fine.

Cams are always shot. 40-60k miles from these. Mine had the original cam at 100k miles and basically it was slower than a milk float.

If you are going to do a rebuild then there are some basic "no brainer" upgrades you can include as the engine was improved over time. I'd look at the following:

1. Change the front and rear seals to neoprene - front is a direct swap, rear require a little machining.
2. Fit a bigger oil pump. You can get a kit with a spacer to fit bigger gears - as you'd of course fit a new oil pump anyway.....
3. Get some later SD1 or Land Rover Discovery cylinder heads, these have bigger valves for a few extra BHP. These can be had very cheaply. As a bonus these has better valve sealing too.
4. Consider a mild cam upgrade. Many offer a few BHP and are more durable than the original.
5. Use a decent duplex timing chain and not the Rover original.
 
I cant think of a UK available 3.9 gm car?

you can get the buick 215 cover from the states with bigger oil pump gears.
 
The Sd1 front cover has an uprated oil pump. IIRC, the uprated pump offered by Real Steel and the like, were based on the SD1 pump.
 
Do you know what gm/ Opel cars it was fitted to ?
Don't know on your side, but in South Africa it was the Chevrolet/Opel Commodore V6.
It used the GM V6 cast iron engine, not sure if it was Odd-Fire or Even-Fire, though, produced until early 80s.
The engine is a 6 cylinder version of the V8 block in cast iron......
 
That never made it here.... The v6s in vectras and omegas are a new engine design... Apparently with an odd angle between the heads.
 
You say oil starvation, did you prime the oil pump? (I don't know how true this is but have heard that the oil pump can drain dry on standing, especially if the engine is old and worn)
 
No I don't think it would have made a lot of difference... the sump was full of horror really thick like tar .... the pick up was partially blocked also and having stripped the engine have found more than one blocked oil way
 
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