Block Decking?

[rallysteve 22]

Now I am gathering the bits to rebuild by XU9J4 engine, I am thinking about getting the block 'decked' partly to make sure the liner protrusion is correct and also to raise the compression ratio a bit ready for some better cams at some point in the future.

My question is, how much is safe/needed to be taken off to get a better compression ratio suitable for some fairly meaty cams?

Also how can I tell how much it might have had skimmed in the past?

 

Cheers Steve

[petert 588]

Now I am gathering the bits to rebuild by XU9J4 engine, I am thinking about getting the block 'decked' partly to make sure the liner protrusion is correct and also to raise the compression ratio a bit ready for some better cams at some point in the future.

My question is, how much is safe/needed to be taken off to get a better compression ratio suitable for some fairly meaty cams?

Also how can I tell how much it might have had skimmed in the past?

 

Cheers Steve

 

The only way to assess these things is with a mock up and measure acurately. You would normally take 0.4mm off a D6C, 1.4mm off a DFW, to achieve zero deck height. Beware that it's not a job for the faint hearted, or inexperienced. If you're near QEP see them. The chances of ending up with skewed liners is high. With that amount you'll end up with around 10.8:1. You can push the pistons through a bit higher and posssibly get to 11:1. Beyond that you'll need hi-top pistons.

 

Also remember that you're decreasing the valve-piston clearance at the same time. So you start chasing your tail if you're after a lot lift @ TDC. Measure carefully however, and you'll achieve good results with matching compression and cam choices. I'd measure up twice. Once for the decking, then again once that's done for lift @ TDC.

[rallysteve 22]

Would a suitable measure be to fit the liners (without seals), clamp them down then fit crank/rods and pistons and see how much clearance there is between the piston and the top of the liner?

 

I dont want to go to insane levels with it. Mainly just want to make sure im not going to have problems with the head gasket leaking and thought it would be a good opportunity to up the compression ratio a bit as I have heard these engines respond well to this. It is a D6C by the way.

 

Many Thanks

Steve

[Jrod 7]

I've got a recently decked block that had liner seats cut by QEP in the forsale section, will save the cost of machine work.

[petert 588]

Would a suitable measure be to fit the liners (without seals), clamp them down then fit crank/rods and pistons and see how much clearance there is between the piston and the top of the liner?

 

I get the block grit blasted around the liner seal area first, to ensure there's no scale or nasty tooth decay. Then do a trial assembly as you say, with no seals. Decking the block is the cheap and easy part, but then taking the liners down so they're square and the correct height is difficult without the right tooling.

[rallysteve 22]

I get the block grit blasted around the liner seal area first, to ensure there's no scale or nasty tooth decay. Then do a trial assembly as you say, with no seals. Decking the block is the cheap and easy part, but then taking the liners down so they're square and the correct height is difficult without the right tooling.

 

hmm, okay cheers I will have a look into it. I am a fair distance from QEP unfortunately, I will have a word with the local engine tuners to see if they can suggest anywhere who could do the work for me. Midland Engine Services have been suggested as being very reliable, although the talk of possibly ruining the liners worries me a lot. Might just measure up and hope the liner protrusion is okay. Will have a serious think, but was hoping to get the compression ratio upped a bit now I am rebuilding so I can just pop some different cams and TB/carbs at a later date without having to strip the engine down again.

 

Thanks

Steve

[SPGTi 2]

Don Loughlin engineering can do this. Very good engine builder (been building race engines since the 60's). Also did quite a lot of work with Dave Vizard. Don is based near Kidderminster (Hartlebury).

 

cheers

 

Steve

[rallysteve 22]

Don Loughlin engineering can do this. Very good engine builder (been building race engines since the 60's). Also did quite a lot of work with Dave Vizard. Don is based near Kidderminster (Hartlebury).

 

cheers

 

Steve

 

Cheers, good to know