dreamer

Well curiouser and curiouser. Just had a call from them:

* Piston number 3 has failed
* An oil seal from the back of the crankcase somewhere has blown out (not recently as it is worn and looks like it's been rattling around for some time)
* There was about half a litre of oil in it

No explanation for excess oil into the catch tank - it's dry sumped so the only reason can be over-oiling but this doesn't really tie in

Recommendation is to also change the liners but apparently the head looks fine and no need for a refresh.

B0ZWELL

there seems to be some confusion over the oil pumps

all the dry sumps i have delt with have three pumps. the main oil pressure pump that feeds the oil galleries from the bottom of the oil tank. then there are two scavange pumps which will pick up the oil from the bottom of the sump (usually one a each end) and feed it back into the tank.

the reason for two scavange pumps is that it must be able to pull all of the oil out of the engine otherwise if one single pump couldn't keep up then the engine will eventually fill with oil.

because the scavange pumps do exactly that, they will pull a lot of air up with the oil. this doesen't matter as the oil tower/tank is also a de-airator. this is why you will see a lot of bubbles (and makes the oil look milky as it is running) at the top of the tank

don't know how you check the level of the oil but it should ALWAYS be checked when the engine is running to get the correct level in the oil tank. dry sump systems are to stop oil surge so i doubt very much that even if the oil level was low there will be oil feed problems. it needs to be VERY low before you get surge.

the oil in the catch tank will be due to blow by from the piston, and normal on a worn or knackered engine, even if it is dry sumped. .

can't help why the engine failed but there has been a lot of talk recently in the historic race circles about modern oils and the removal of some catalytic harmfull chemicals. a customer has had long talks with oil companies in America after his newly built 1965 600hp 7litre Chevy engine failed at Spa quite spectacularly . the bearings failed , it threw a rod through the block but it also snapped the camshaft which went on to bend the valves and damage the heads. the engine is scrap.

the conclusion was to use a monograde oil and an addative . the reason was that a monograde oil has stronger bonds and the addative is to help protect the bearings. race cars are warmed up before the race so a multigrade is not needed at all. and change the oil very regulaly.


hope you can find the cause of your engine failure , doesn't sound good at all.

Nick Graves

They used to heat the oil and add it to the engine at the last minute, in order to get it to work properly!

dreamer

Boz - you don't check a Caterham dry sump with the oil running. In case anybody needs to know, you run the engine up so the oil is up to temp. Take the dip stick out and clean it, then turn the engine off and dip it quickly.

Reason for this is the conning tower (where the dip is) has the oil swirling around in it while the engine is running (I believe it helps get air out of it as the scavenger picks up oil & air like you say). So if you check it with the engine running you get a false reading.

Maybe different dry sump systems have the dip in a different place, but on the 7 it's part of the cap for the tower.

I think I have two pumps; one is the scavenger pump, and the other is the actual oil pump.

I think the opinion at the moment is that the cracked piston is what has caused the failure, although the blown seal doesn't appear to be related. Hopefully more details tomorrow.

B0ZWELL

remember i only work with old bangers

most dry sumps iv'e worked with don't have a dip stick. the 'D' type does but the '55 workshop manual states a revision where the dip stick is not used and just a visual level check to one inch below the upper baffle while the engine is running.

switching off and immidiatly checking will be about the same though

but to be honest i wouldn't have thought that the level will be that critical as long as it isn't too low.

Nick Graves

Do we know what went on the piston yet? Especially if they're upgraded.

Has it done an F20c and the rings picked up, which might bring us back to the oil...

lower

[QUOTE=dreamer]I think the opinion at the moment is that the cracked piston is what has caused the failure, although the blown seal doesn't appear to be related.

Nick Graves

More coffee required.

So much for upgraded slugs...

ge2

Ironic, my standard pistons have been a worry since I bought the car, they should have let go ages ago.

Jo's got the proper ones, they break.

I've got a set now though, they're ever so pretty

dreamer

Long story I won't go into details on here but pistons were standard........

Not sure of exact failure - going to call the guy tomorrow - today they were still stripping it