Cam Knock/tap

[lemmingzappa 75 1 Cars]

Well I've had the engine apart today and it looks like cylinder 1 has some scoring to the walls and the piston isn't sitting straight at all, probably due to the broken rings.

 

Where would you guys recommend I buy new liners and pistons? (I assume I should be replacing all 4 whilst i'm at it).

[welshpug 1,627]

Anywhere you can get hold of them these days! indeed it would be daft to buy 4 and only fit one.

 

now is the ideal opportunity to get hold of some 1.6 pistons and liners to push the compression up so the cam will work properly.

[lemmingzappa 75 1 Cars]

Ah ok thanks for the advice. I assume that would still be the case with the XU10 head (sorry i'm not too clued up on compression ratios and how they work).

 

Looking around online, some places list the liners as both 1.6 & 1.9, are these just incorrect descriptions?

[welshpug 1,627]

if they are bare liners without pistons then it is correct, however with pistons then it is incorrect.

[lemmingzappa 75 1 Cars]

I see, so the liners are non-specific. Only new 1.6 pistons I can find are those 'Forged Wossner' jobbies, expensive

[welshpug 1,627]

with engine bits, you need to go old school, you're not likely to find anything on the internet, old dog and bone it'll have to be!

 

 

as for your current compression ratio I have no idea, depends what the difference is in chamber volume from XU9JA to XU10J2, but as standard with a 1.4mm gasket they are 9.6-1.

 

 

those forged wossner are cheap tat from all reports I've heard of them from people who know how to build proper engines!

Edited October 5, 2013 by welshpug

[lemmingzappa 75 1 Cars]

Just for reference, here's a pic with the flash on. You can see some wear to the top right of the piston which has eaten in to the liner, and the offset of the piston.

 

http://imgur.com/rse0wUq

[cheesegrater 43 1 Cars]

I'm pretty sure iI have a set of pistons/rods in my garage if you want them.

[Anthony 1,000]

Compression ratio on that engine should have been around 10:1, although it was always a slight question mark over how much was actually skimmed off the head by QEP and I think that it was considerably higher than that - my best guess is around 10.5:1 but it could be higher.

 

Certainly the CR was high enough that a standard 1.9 dizzy was not ideal and needed to be run retarded, and a static compression test was around 220psi.

 

I would strongly suggest not running pistons with reduced dish sizes (e.g 1.6 XU5JA) as that will make the CR excessive for the cam and you'd likely have no end of issues with ignition timing. Indeed, possibly lowering the CR slightly (e.g 1.9 CAT XU9JAZ pistons) might be beneficial, but replacement 1.9 non-CAT (XU9JA) pistons should work nicely as that's what's in there now.

 

Shame about the liner damage, as that makes it a rather more involved repair. As above, makes sense to replace all four liners and rings as a matter of course - you could, certainly until recently, get very reasonably priced liner/piston/ring sets that's the route I'd go down... assuming you don't just swap the entire bottom end over and just reuse the existing cam and head.

[lemmingzappa 75 1 Cars]

I'm pretty sure iI have a set of pistons/rods in my garage if you want them.

 

Which ones do you have Tom?

 

Compression ratio on that engine should have been around 10:1, although it was always a slight question mark over how much was actually skimmed off the head by QEP and I think that it was considerably higher than that - my best guess is around 10.5:1 but it could be higher.

 

Certainly the CR was high enough that a standard 1.9 dizzy was not ideal and needed to be run retarded, and a static compression test was around 220psi.

 

I would strongly suggest not running pistons with reduced dish sizes (e.g 1.6 XU5JA) as that will make the CR excessive for the cam and you'd likely have no end of issues with ignition timing. Indeed, possibly lowering the CR slightly (e.g 1.9 CAT XU9JAZ pistons) might be beneficial, but replacement 1.9 non-CAT (XU9JA) pistons should work nicely as that's what's in there now.

 

Shame about the liner damage, as that makes it a rather more involved repair. As above, makes sense to replace all four liners and rings as a matter of course - you could, certainly until recently, get very reasonably priced liner/piston/ring sets that's the route I'd go down... assuming you don't just swap the entire bottom end over and just reuse the existing cam and head.

 

Thanks for the info mate, I have much to learn about internals!

 

Would I need to get the dizzy re-curved again after the rebuild, or would that only be the case if I used the 1.9 CAT pistons?