706 replies to this topic

[smiley]

He has no choice me thinks. All his money is parked on lee's driveway.

[MartinS]

Its been crap for 5 months, waiting for it to improve is becoming the norm

[smiley]

2016 FTW

[Graeme Lambert]

Definitely 2016 FTW

[Matthew Bentley Racing Ltd]

Me and lee both on it on Saturday.

[ultimate]

I disassambled my oil-using B207 yesterday. It was a brand new Engine, not a rebored or something like that. At the end it used 1l/500km when just cruising around... Under load it was much more...

DId aorund 11.000km with Harrop.

 

Thats what i found:

 

Compared to another  brand new B207:

 

I cannot post pics here, but the cylinderwalls and pistons are looking okay. No excessive wear viewable...

Edited by ultimate, 11 December 2015 - 08:23 AM.

[fezzasus]

I wouldn't read too much into that as long as your piston rings are not stuck.

 

Basically, the bedding in process will remove any excess material which stops ring movement and allow the piston rings to move in and out easier, this means the pistons will rock 

[chris_uk]

And allow for expansion i guess

[fezzasus]

And allow for expansion i guess

 

It should allow for expansion when new, otherwise the engine won't last that long, so that doesn't account for the difference. It's purely resistant to ring movement.

[TFD]

Dont know if you have rods and pistons out, but I would meassure the piston to wall clearance. On my forged built blocks there is more clearance due to expansion of the forged piston then stock. You can hear this as "pistonslap" when cold, all is well when warm. But sure not as much play as you have.

Check the ciliinderwall at the bottom were the piston stops, could be a thin line/edge in the cilinderwall what will be the result of wear.

 

Basicly run some basic test first.

[TFD]

Why cant I edit my previous post?

 

Anyway:

 

If its in the combustionchamber, I would take rods/pistons out and start meassuring it al up and check if all in within specs. 

Check pistonrings, check pistonwall for edges etc. Basicly your basic checks.

Bit of movement CAN be ok (tapered piston top), just make sure what is ok and what is to much.

 

Allways a sh*tty thing to search for something if you're not sure what you're searching for... Good luck.

[fezzasus]

Honestly, if there's still honing visible then there's no point taking the pistons out as there's minimal wear.

[ufods]

The honing is still visible! ( there are some pictures in the german Forum ) But, where is the error ??

[fezzasus]

Check for stuck rings.

[Exmantaa]

I saw the bore pics on the German forum and his bores crosshatch still looks fine.

 

But I agree that his first suspect would be the piston rings (stuck), because a piston should not rock and stay on one side like that, if the rings function properly. The piston can have some play, but think it should always center back due to the spring tension.

 

Stuck rings explain the rocking AND explain the massive oil consumption. Possible caused due to excessive cilinder pressures with his restrictive exhaust (265KPa MAP!), but unsure if that was before or after the oil consumption started...

 

[smiley]

Hopefully Martins engine will be opened up this weekend as well.

If that also has rocky pistons we have a pattern...

[Exmantaa]

Well, I have an old Z22SE engine (old 98K miles engine from the project car) that had the same "loose rocking pistons". Never looked further into that because replace by LSJ, but it could lay HUGE smoke clouds with some throttle and had massive oil consumption... Inside of the head had lots of carbon build up like Ultimate's.

 

(Not sure if they will open-up Martin's engine that far, but I'm quite sure this would have affected his good compression test results.)

@Ultimate; did you do a compression test on your engine when you had the consumption problem?

[ultimate]

My 265kpa was with the 3"inch tullet. This has nothing to do with the exhaust backpressure. It is the result of 70mm pulley and unported head. Oil consumption was very much before I used the n/a backbox for short time. The Piston rings are all free... Will post some pics and measurements in the next days...

[fezzasus]

Any news?

[Nev]

Having read some of the posts above, people need to be aware that it is normal for pistons to rock in the cylinders.

 

Importantly, piston to bore clearance is rarely/never measured at the crown (which is where you guys have been observing it), instead they are measured at a manufacturers specific height some considerable distance below the crown, often a bit above the gudgeon pin. This is because pistons tops are tapered to deliberately allow a rocking motion.

 

On a forged engine the piston to bore clearance will likely be close to double that of a cast piston due to the greater expansion requirements of the alu in the pistons, I'm not sure what pistons this guy has, but if they are forged then the gap will be larger (and static rocking motion be be consequentially larger).

 

HTH. I can't believe how long this thread is BTW !