DOO

I was told by the chap i bought the car off that it had low compression piston fitted when it had a full rebuild.
How can i tell do a compression test or not ??

cossie1

afaik the only real way you can tell is by removing the head. altho I could be and probably am wrong

Glenn5

Do a compression test m8 the figures will reveal what you have m8

SPADGE

Doing a comp test will only tell you what the comp is and not the ratio!
The head needs to come off i do believe for anything else!

Karl

A compression test will reveal nothing in terms of identifying compression ratio.

The only way to verify if you have modified pistons is to remove the head and burette the piston crowns for volume.

DOO

I think i leave it at stage 3 then for now.Only done 5000 miles since rebuild.Can`t be fooked to take the head off to find out

Cheers for the info lads anyway

AndyRST

Tony, why dont you phone bluesprint motorsport. Im sure if you give them the car details and reg etc they will have a record of it. I know the previous owner was a little fussy when it came to rebuilding that engine Im sure he didnt do things by half

GARETH T

anyone ever tried to do it thought the shark plug hole? even though it would be tricky

James

It'd be difficult to get out whatever you put in then though.. ?

Karl

No can do gareth.

Piston rings can leak fluid giving inaccurate results.

I can do it this way if its a dummy build whereby I have filled the top ring area with grease to prevent fluid leakage. However its easier to simply burette all volumes rather than a dummy build just to measure C.R.


Hence on an engine thats in car its a no go.

DOO

The only prob mate it was a cash job no invoice .I spoke to joe @ BLUESPRINT But he can remember the car and rebuilding it but not a 100% sure what work was done on it.

He did tell me the previous owner was fussy as fook though.

As i do trust the guy i bought it off was telling the truth i just wanted to be 100%.

Look like i may have to take the head off

AndyRST

From memory the story goes something like this: They rebuilt the engine and before it was even run in the previous owner took it back to them and made them rebuild it again because he was unhappy about something minor thing with it

So yeah i heard he was a little fussy

Glenn5

You could still do a comp test 2 see what the figures are if there all the same across all cyls and are low or high will help denote health of engine and will help explain whether low comp or std it wont give a comp ratio but will help

RSrussell

what does buretting involve? I know what it does and heard the term use for ages but never actually know whats involved

Karl

Glenn5

NO it wont determine whether its std or low comp in any way!!!

DOO

He did say he had to get the piston`s from germany.But that don`t mean anything to me

GARETH T

Karl,

i was thinking baout the rings leaking!

Glenn5,

you gotta think about what effects the compression test, cam timing, cam choose being just two

smartrs

sorry to jump on your post but its kinda related , would anyone in the know say thease are low comp pistons ?? as i was told by the last owner that they are but am not sure ??

Glenn5

SAD V .SAD

RSrussell

wtf

Karl

smartrs, they look like std 4X4 pistons that have had valve cutouts machined into them, but I can't say for 100%!

GARETH T

Glenn5,

wrong v wrong

smartrs

thanks karl thats all i need to know i hate having a enging that i dont really know the spec of , all i know is that it needs a set up and hopefully some one will be able to shead some light to the spec and what it caperble of ?

Glenn5

WTF is a compression test 4 then if not 2 determine whether you have high or low comp on each cylinder.

Fudgey

iTrader: (4)

only way to tell is to remove head

Stavros

DOO= Does it matter? You can go well past stg3 on std comp anyhow if live mapped, and TBH if u was going past stg3 youd idealy wana whip the head off to fit a decent gasket anyhow.

bob s2zvh

how can you tell with the head off? i'm away to buy a low comp bottom end 2! had a quick look at it a few weeks ago and the pistons were dished! how deep should the dish be? or would the pistons just sit lwoer from the top?

Karl

Glenn5, I'm affraid your attitude is pretty poor!!

A compression test is used to test for leaking/bent valves or damaged/cracked piston rings. It can give an indication of general engine health IF you know the compression readings when the engine was new.

It is a very crude test simply to help identify if the engine has any obvious internal faults which would then require stripping to investigate.

Glenn5

If you want ratio's take the head off. If you just want to know whether its High,Low or standard compression then do a compression test.

Simple really.

Karl

Glenn5,

You really don't get this do you. You're either stupid or have'nt read what I wrote above.

A compression test does NOT tell you whether your engine is high or low comp.

If you can't accept this I will give you an example that will help explain why it's of no use.

As I've said its a crude test to help identify IF a problem exists in the engine. The results do not indicate the C.R.

Fudgey

iTrader: (4)

low comp pistons are dished, only way to tell is to take off head

Stu @ M Developments

iTrader: (12)

Karl is of course absolutely correct Glenn M8

Glenn5

Like i said above if you want ratio's take the head off.

The question wasn't how do i determine ratio's just the compression.

Is anybody on this post to help or are we here just to bitch at each other?????

Karl

Glenn5,

Don't get all arsey because you're wrong. We are'nt all born knowing what we know! It's a learning curve for all of us including me and stu!!

Stu @ M Developments

iTrader: (12)

Glenn.
If you do a copmpression test and its low at say 120PSI. How will that tell you its a low comp set of pistons?

How do you know the valve's arent leaking or the piston rings not worn? Maybe even the followers are knackered and causing a low reading.

Stu @ M Developments

iTrader: (12)

Its been a while, but tonightr ive learnt that after only 5bottles of beer, i cant type properly... quality!!

James

Glenn, I think you'll find he wants to know if he has low compression pistons or not, meaning a low compressin ratio as opposed to how much actual compression there is in there.

Karl

Not to mention stu the cam timing could be well out from factory, due to variances in manufacture, head height, and even the odd case where people have got the cam a tooth out!! lol

Stu @ M Developments

iTrader: (12)

Whats odd aboout it? I find it more a "Normal" ccase.. roflol

DOO

Stu not geting into this argeument i may be wrong but the engines only done 5000 miles since rebiuld and running fine no knocks a rattles.
so i don`t think anything would be wrong.

so is it worth doing a comp test or not