Problems with pistons and block :( [Archive]

robi1000

22-11-2008, 21:55

Hello!

I have a slight problem and I would like your opinion. I've got round to putting my BE together and now my pistons are cca. 1.8mm over the top of the block.

http://shrani.si/f/2G/zt/xk3XWOg/22112008001.jpg

http://shrani.si/f/3J/fY/1jEsxDrm/22112008002.jpg

http://shrani.si/f//6z/1RPw7p89/22112008003.jpg

Obviously block was skimmed (don't know what else could it be). So how would you guys solve this problem? I don't want to buy another block, because prices here are crazy for F7R engines and I've already spent a lot of money reboring it to bigger bore. Could I use some sort of spacer, similar to those for turbo use? What do you guys think?

richy

22-11-2008, 21:58

what pistons are you using mate?

also are you using the std crank/rods for the block ?

Brealbags

22-11-2008, 22:00

woah thats a bit wild. Shouldnt be any need for skimming the block. Had the head skimmed cos its aly and increases comp ratio.

Maybe oversize big end bearings would help?

robi1000

22-11-2008, 22:39

I'm using Wossner 9034 pistons and std conrods. Don't know why anyone would want to skim the block, but hey that's the way it is and I have to deal with it. Currently I have two ideas. One is a spacer (sort of a metal gasket similar to turbo ones for rising CR) and another is to skim this pistons. But I'm a bit more inclined towards the first solution. Any other ideas? Will this spacer work?

richy

22-11-2008, 22:47

if your using the std conrods/crank are you sure it isnt the wossner pistons, pos wrong set? do you have the std pistons to compare?

obviously thats if it hasnt been skimmed several mm!

robi1000

22-11-2008, 23:00

Well, I'm sure they're the correct ones because they have model number engraved on top. So the only explenation would be that the block was skimmed.

sideways danny

23-11-2008, 14:27

are they oversize F7P pistons intended for a shorter stroke by any chance?

robi1000

23-11-2008, 15:19

Well as I said, they have their model number engraved on top and I checked this before I had my block rebored because it would be very inconveniant to rebore my block for wrong pistons. So pistons are definetly correct ones. Question now is if it's possible that I'd have longer throw crank. Are there any such cranks in renault portfolio? IIRC conrods should be 144mm long for F7P/F7R and MAXI rods 150mm?

What is the height of the block (absolute, from bottom to the top if you'd put block on the floor)?

If I diagnose that my block was skimmed (most probably), could I make an adapter plate in the shape of HG, say 3mm high to compensate skimmed block?

Looking forward to your answers guys! Your help is much appreciated. This car is cursed...

adam 006

23-11-2008, 15:57

If you have the correct rods,pistons and cranck then the block is junk.

Also to skim a block down that much would be very odd

Brealbags

23-11-2008, 18:29

how would a spacer work to go on top? surely u wouldnt get a proper seal.

adam 006

23-11-2008, 20:34

how would a spacer work to go on top? surely u wouldnt get a proper seal.

some times people use a twin head gasket system to reduce comp ratios when turboing na motors

Brealbags

23-11-2008, 20:52

ok i thought it was the design of the pistons that reduced CR and it was just like an uprated gasket.

number1

23-11-2008, 21:02

wouldnt like the idea of a Piston going up past a Gap in between a spacer plate and the block... How much did they take of the Block? block skimming is only done to ensure that its true across the face

Dave

number1

23-11-2008, 21:05

This is a Standard Block look how much closer the F7r Writing is closer to the Deck on yours...

number1

23-11-2008, 21:30

Doh Add the picture Dave!!
http://img.photobucket.com/albums/v602/davebell1984/100_0143.jpg

robi1000

23-11-2008, 23:05

Can somebody please tell what is block height? I know it's hard to measure accurately but I think 2mm is quite noticable so I should be able to measure the difference.

MAXIBOY

24-11-2008, 00:05

hi mate..

minimum between joint faces 281mm

height between bearings axis and cylinder joint face 221mm + 0.05mm

MAXIBOY

24-11-2008, 00:25

plus lots of pistons especially high compression ones do run into the gasket space..

but 1.8mm sounds a lot think there's a 1.6mm of the shelf gasket..

can't remember what the standard one is..but looking at yours i think if the outside edge is no more than around a 1mm then you should be fine..
the rest runs into the combustion chamber..

but p.m stan and ask mate

robi1000

24-11-2008, 00:34

Does anyone have any experience with using two HG? That should give me enough clearance. Or if someone could tell me how thick metal HG would have to be if my pistons are 1.8mm over deck? I'm thinking about custom metal HG?

snowman

24-11-2008, 00:35

Think the standard gasket is 1mm and the uprated and turbo ones are 1.6mm

MAXIBOY

24-11-2008, 00:48

need to be sure as they will also stretch at higher rpm...but not sure how much mate..plus you need to be sure on valve clearance mate

Wobba

24-11-2008, 01:31

From the look of your pistons though, the outer edge would only just push to the level of the gasket, and the mid section would have clearance due to the dome inside the head itself. Assuming the valves are all shut at peak piston travel, it should be ok I imagine. I am no expert though so wait for people in the know...

robi1000

24-11-2008, 08:32

Just a quick question... Apart from bore size, what is the difference between F7P and F7R block? I think there are other differences but can't remember now.

MAXIBOY

24-11-2008, 10:28

not sure on them all but the 2.0 litre has the extra strengthening ribs on the back..

plus has a load more clearance at the base of the bore as standard a 2.0 crank and rods won't turn in a 1.8 block..

white16valver

24-11-2008, 10:46

Different crank I think?

Can you get someone over here to ship another block over to you? I'm sure Matbrown or similar could get their hands on a good one!

robi1000

24-11-2008, 13:01

Well they would have to be very cheap, because postage costs would be quite high... :(

2 live

24-11-2008, 17:32

i have a few spare blocks i might have to get rid of soon.........watch this space lol.

does look like the blocks been skimmed tho on urs. maybe the angle of pic makes it look that way.

number1

24-11-2008, 18:25

Can you get a pic of the rear of the block like mine? we should be able to tell then roughly how much has been removed

Dave

stan

24-11-2008, 19:04

you need to measure the crushed gasket thickness, and from this work out how much to lathe off the piston crown to give the desired squish clearance.

I would expect the crushed thickness to be 0.7mm or there abouts, thats what they are from the gaskets I use anyway, but this may vary between manufacturers.

You defo dont need a new block lol.

They are 100% for an F7R as I sold them to him as used parts. They had a 0 crown height when I had them fitted so yes your block has been decked.
If they were for an F7P they would be nigh on 5mm higher than the block :lol:

robi1000

30-11-2008, 21:57

This is a question for you turbo guys. Lathing my pistons is my last resort so before that I'd try to solve this problem with thicker gasket. So what do you guys use for low boost? Can you put two metal gasket one over another and get a good seal? How much these metal gaskets compress over time?

adam 006

05-12-2008, 23:21

in my opinion there is no easy way round this problem.I think you should scrap the block and start again

stan

06-12-2008, 10:24

Based on what?

volymmannen

06-12-2008, 13:21

Just a quick question... Apart from bore size, what is the difference between F7P and F7R block? I think there are other differences but can't remember now.
the engine block is higher, no oil cooled piston

volymmannen

06-12-2008, 13:25

F7P 82*83
F7R 82,7*93

robi1000

06-12-2008, 13:59

Well I ordered a custom HG and we'll see if it'll work. :)

stan

06-12-2008, 15:02

the engine block is higher, no oil cooled piston

:?

volymmannen

06-12-2008, 18:04

the engine block is higher, no oil cooled piston

:?
F7R block

stan

06-12-2008, 18:48

what about it?

Block height is the same, and both have under-piston oil sprays.

adam 006

06-12-2008, 23:03

Based on what?

based on.time,money,skill and the over whelming feeling i have in my water that something is not right with that block.But all that said nothing is impossible

robi1000

07-12-2008, 00:49

Adam you're right! Your water must be some very special subsance... It's not just the block tho! You see, something is not right with the whole car. It's cursed. :lol: (I'm serious)

But I like it anyway. If I go in your order:

- Time : This is my project car so I have plenty of time.

- Money : Trust me you'd want to avoid buying new BE if you would live in Europe

- Skill : Well, my skills are nothing special, but the easiest way is just to buy new block. Or you can try and do something about it and learn in the process.

adam 006

07-12-2008, 23:21