Clementine's Garage
Clementine the Cat
 
Image of flower
Yellow R4
 
home my cars restoration tech tips guides forum
Réparateur d'automobiles

Piston removal

C

ChrisH

Enthusiast
Messages
106
This may be a daft question, but is it possible on an 845cc engine to remove the pistons down through the sump or does the crankshaft and crank webs get in the way?

The reason I ask is that I may want to change the piston rings without taking the head off, thus not being in any danger of disturbing the cylinder liners.

The obvious and sensible route to take is to take the head off and give it an overhaul, make up some clamps to hold the liners down and then pull the pistons up.

In the event of liners getting disturbed, are liner bottom seals readily available, does anyone know?

Would appreciate comments/answers to both queries - thanks in anticipation.

Chris
 
The crank would get in the way trying to do it from the sump, and in any case you wouldn't get them back in again.

Free the head by knocking it sideways with one bolt still in (but loosened a little) then clamp the liners before you turn the engine. I use thick washers bolted where the head bolts in.
 
Thanks Malcolm, and renoir cigar, the use of washers is a useful tip as it saves having to make up some clamps. I will go down that route.

Chris
 
Hmm, I guess, I can give you some good advices.

Unfortunately they might sound like the grunt of a vandal. I'm german - we are unable to express things in a gentle or diplomatic way.

1. Reed Malcolms article about how to ruin a new piston and conrod in less than two minutes (Gordini Projekt).

2. There is no need to look only for pistons. Pistons and liners are allways changed together. They are so cheap that it is unprofitable to mess about with pistonrings, wich are relative expensive.

3. If new pistons and liners are reasonable can found out by pressure test and with a endoscope.

4. If you find out, it's really time for new pistons go to point 1. It's not possible to work on Renault B or C-Engines without experience and special tools. Especially to disconnect and connect pistons and rods is difficult and the liners have to be positioned very accurate.

5. All this can be done with the engine in the car. Theoretical. But It's absolut no fun. Better get the engine out and take advantage to look for things like clutch and sealings.

6. How long does it take to get the engine out and to assemble it again? In very much depends on how often one has to repeat it ;-)
 
be sure you get the conrods/pistons back the right way round ! I didn t and the knock was incredible !! good luck
 
elch101 said:
5. All this can be done with the engine in the car. Theoretical. But It's absolut no fun. Better get the engine out and take advantage to look for things like clutch and sealings.
Click to expand...

Our friend is absolutely right, the "fun" part is relocating the sump and its four piece gasket in the first place, then effecting a good seal-LOTS of patience and luck needed.
WAY easier and safer to remove the engine!
 
Hi All, sorry, been away hence no replies. Thanks for all the replies, has given me good advice.

Have decided not to remove the pistons just yet. Am going to do a head job and then see how she is, give her a good run and put a put a compression test on when I get to France (where all my kit is). The engine has only done about 43 and a bit thousand miles so the pistons/rings should be good, but who knows, I don't until I test it. Anyway, by then she will be in France where I will have more facilities available, like a garage with heat, light and power and tools, and the loan hopefully of an engine hoist, should I need it, here I just have a very small garage, end of.

I will measure the piston side clearance whilst the head is off, hopefully it will be OK as I don't want the expense of a set of new pistons and liners plus the refitting of the conn rods to do; have a set of rings, hopefully that will be enough. Lot of 'hopefully's' in there!

Chris
 
Some more vandal advices:

Easyest test is to messure the oil-consumption. This has to be done very accurate. That means at least 2000 km and the car has to stand really straigt line. 1/4 l/1000 km is normal. 1/2 l/1000 km is barely ok. If you're inbetween this nothing will be wrong with your pistons. The engine is desingned to last for 300.000 km.

To take of the head is a good chance to ruin the sealings at the bottom of the liners. Than you have to demount the hole engine. Maybe someone else want's to explain how to take the head of.

What do you see with the head of? Nothing that can't be seen with a endoscope as well. The clearance of the pistons will be more than you expect because they are a little bit thinner at the top end.
 
Hi elch101, I am not going to take the head off just to take a look. I agree if all I wanted to do was look I could use an endoscope, if I had one which I don't . I am going take the head off to check and lap in all the valves so that I know they are in good condition. Then if a compression test reveals a cylinder is poor then I know it is the piston/rings not the valves.

And I have done head overhauls on these engines before, I know of the dangers of disturbing the cylinder liners but have been successful in not disturbing the liners in the past, I hope I continue to be so.

The engine had a report some time ago that one cylinder at least was down in power, I do not know if anything was done about it since but I will at least ensure something is done now.

Thank you for your advice on oil consumption, I will check that out as time goes by.

Chris
 
My general idea is: As long as the engine is running its much easyer to do precise diagnostics. There is a compression test called "falling-pressure-test" in german, that shows exactly where missing compression is gone.
The things that can be mesured on a running engine are more significant than the things one sees by deconstruction. An example: On older B-type engines you often will find a crankshaft that doesn't look nice. New or reconditioned crankshaft, bearings, new screws for the conrods... al in all 600,- Euro or so. If you can messure the oilpressure before you often will find out it's perfect anyway and the engine will be fine for another 100.000 miles.
The trick with the head is difficult to explain to me, but i'll try: One screw in the middle of the head, distributor side, is left. You loose it only a little bit so there is still a little grip. Than you loose the head with a hammer crossways. Than you can remove the last screw and the head. It's really important not not move the crankshaft untill you have the clamps fixed.
 
You must log in or register to reply here.
Community platform by XenForo® © 2010-2024 XenForo Ltd.
Back
Top