Piston protusion

[Ben]

I was about to crack on and fit the head onto my block today, but I've just noticed that the 4th piston doesn't protrude from the block surface as much as the other three.

Pistons 1,2 and 3 all stick out about 1mm. Piston 4 does not stick out, it remains about flush with the block surface.

Am I right in thinking this is going to cause a big difference in cylinder compression and cause a rough running engine?

Can't think how this has happened because the pistons were all removed from the same block and the HDI rods were also a matching set.

Really hope its nothing to worry about! Any thoughts appreciated..

[Dave]

Dan rang me about this, the only explanation I can think of is one of these...

• The crank is bent (highly unlikely, and would be a bastard to assemble/turn over)
  
  
• The conrod is bent (again it could be mildly bent but certainly not enough to shorten the length of it by 1mm)
  
  
• The shells are missing/little end bushings are f*cked/lots of slop
  
  
• The pistons are not all equal - and I suspect this would be the killer...
  

There is only 2 things it can be, just check these

[Ben]

I was hoping that I had been a tard and forgotten to put a shell in, but I just checked and sadly I'm not a tard.

Little end bushings are fine.

Rod doesn't look bent but I will take it out tomorrow for a good check.

As for the crank being bent, I bought the engine as a good running engine, and the rods I took out of it were fine, which would suggest it wasn't bent else they would have been mullered? It's not too hard to turn it over, but does get slightly stiffer when all four pistons are in line, that normal?

I'll also check the piston lengths, as this seems most likely to me as well. It would also be very strange though because the pistons are a complete set out of the same engine, and a whole mm shorter is a lot!

Cheers for your reply, I'll report back after further investigation.

[Tom]

Interesting problem here! Look forward to what you find. Best of luck chap

[Ben]

I'm not finding it interesting! I look forward to getting it sorted though, thanks for the luck I may need it!

[londondan86]

I could be way off here but are you sure the block surface is completely flat?

[Matty]

I could be way off here but are you sure the block surface is completely flat?

I'd think you'd probably notice if the surface wasn't flat. As if Piston 1, 2 & 3 are at one level, then 4 at a different. That would mean the surface is fine until number 4. I don't think a drop of 1mm is going to be likely, and would be fairly noticeable I would of thought! Might be wrong though...

[CJ_Derv]

Really strange this, hope its something simple to fix dude!!

[Jake]

Just helped take the rods out, number one Is definitely as bent as Louie spence

[CJ_Derv]

Ahh simple fix then just got to source a rod could have been worse, glad it was an easy find guys!! Is louie spence really bent?? Jus seems happy haha jks

[Dave]

Wow thats impressive bend!! Get photos. I would replace all... If they are from same block most likely all bent a little

[darrenjlobb]

As Dave said, replace the set, good job you noticed it, as that motor wouldnt have lasted 5 minutes! Alot would have glanced past it, so add some man points

[Dave]

Following advice darren gave me, I always check my rods prior to fitting by sliding a gudgeon pin through two of them, and sliding them together. They should meet flush at the little end and the big end.... if there is a gap at either then at least one of them is bent...

[darrenjlobb]

Following advice darren gave me, I always check my rods prior to fitting by sliding a gudgeon pin through two of them, and sliding them together. They should meet flush at the little end and the big end.... if there is a gap at either then at least one of them is bent...

Which is the case alot more often than people might first think!!! ^^

[Dave]

Yeh I pulled a set of hdi rods out of a block, completely stock with 157k on it, and they were all scrap as being a fraction bent I didnt wanna risk it!

[darrenjlobb]

cheesy stock rods, the bigggest issue with all psa dervs!

[Ruan]

Christ, does prove that there was definitely a fault in the forgoing process when some rods were made...

[Ben]

Cheers for all the replies guys. Glad I've found what seems to be the fault, incredibly suprised the bent rod made such a difference up top though! I'll post a picture of it soon, because I'm not really sure how bent a very bent rod is!

[darrenjlobb]

This is a point ive been making regarding bending stock rods / decreasing compression making them safe again / loose power, then tuning it back up to compensate, then bending them more etcetc until they let go, this is how all xud's ive had have died, but people never believe me that bending the rod can acaully drop the comp enough

[Ben]

Well I'd certainly believe that it would drop compression, just suprised it brought the piston down a whole mm! I am quite suprised how far they come out of the block though, I know they are supposed to but surely they would touch the head!?

[darrenjlobb]

Head gasket is quite thick...u don't need much squish gap

[Ben]

I just assumed the gasket would get squished to way under a mm