Piston arrow direction

[Brit01]

First time builder here.

When I cleaned up the 2mm of baked oil and carbon off the pistons I viewed arrows and letters on the pistons. As far as I remember 3 were pointing downwards and 1 upwards! Something wrong there for a start but could be mistaken with the arrows.

I have read that the left bank pistons should point downwards and the right bank upwards in relation of the crank movement.
Some other people have told me they should all point downwards towards the exhaust valve.

Re-assembling is causing me some concern and want to make sure everything is done perfectly as I've spent some money on new camshafts/tappets/rings etc. and want the engine to run another 100K without issues.

[WhizzMan]

What engine are you building here? I think your directions with "banks" are for a V8? Sometimes, arrows are not pointing towards exhaust ports, but in general they are. It's important that you state what engine you are building. Otherwise, nobody will be able to tell you for certain.

The bearings and crank in your lower picture don't look very good. There is a green circle around some damage that I myself would not want to assemble an engine with. The "brown spots" on other journals on the crank could be dirty oil, it's hard to tell from the picture. They could also be damage?

Are you going to fix those before assembly?

[TomLouwrier]

viewtopic.php?f=4&t=2564
Alfa boxer 1.7 8v (1988)

These arrows are there in order to get pin offset right in relation to crank rotation.
All towards exhaust valve would seem logical, but only in a line engine. In a boxer or v-engine it would mean the factory has to handle left and right handed pistons. Design, identify, order, stock, administrate, pick and assemble, distribute as spare..... etc. Very complex, very expensive.

Better to get just one piston (maybe even common with other engine models) and document the right way of fitting them.
The book must be right: one side arrows up, the opposite side arrows down.

Makes you wonder who put the one in upside down. Factory mechanic?

regards
Tom

[Guy Croft]

This engine is a flat-four Alfa.

The question of 'bank' is difficult. Some (incl all F1) name the right and left bank as viewed from the flywheel end and this may be the case here.

Does the top sketch below make sense?

If that doesn't help examine the position of the pins in the pistons - they will likely have a thrust offset (for quiet running) as shown in my second sketch and if you set the things out on a worktop with the offset in the right place it should be clear enough. If the direction of crank rotation is indeed clockwise then n the right bank (again, as viewed from crank nose) the pins will be offset to the top of the engine and on the left bank offset to the bottom of the engine.

Print my sketch and rotate it and you will see what I mean.

G

[Brit01]

The bearings and crank in your lower picture don't look very good. There is a green circle around some damage that I myself would not want to assemble an engine with. The "brown spots" on other journals on the crank could be dirty oil, it's hard to tell from the picture. They could also be damage?

this was just an example - not my crank thank unacceptable. I will take a pic this weekend before I reassemble anything.

This engine is a flat-four Alfa.

The question of 'bank' is difficult. Some (incl all F1) name the right and left bank as viewed from the flywheel end and this may be the case here.

Does the top sketch below make sense?

If that doesn't help examine the position of the pins in the pistons - they will likely have a thrust offset (for quiet running) as shown in my second sketch and if you set the things out on a worktop with the offset in the right place it should be clear enough. If the direction of crank rotation is indeed clockwise then n the right bank (again, as viewed from crank nose) the pins will be offset to the top of the engine and on the left bank offset to the bottom of the engine.

Print my sketch and rotate it and you will see what I mean.

This makes sense now Guy. Yes as the manual says.
Due to the offset and direction of the piston in relation to the crank when in firing 'mode', makes sense to point the pistons down on the left and up on the right.

I'll check the offset of the pins this weekend.

Well about the mechanic - he supposedly did a sketchy rebuild as I'm finding out now while taking it apart.
Most of the time he directs his employees to work on his engines. Someone made a mistake I believe. Unfortunately there are very few people who know anything about Alfa flat fours here. I have found another good mechanic just 2 blocks from my house. He worked for a UK racing team for 8 months. He has a beautiful E-type Jag in his garage in restoration. What a beauty. He had all the carbs polished. I was dribbling over it.


Thanks very much.

[WhizzMan]

I have just verified this all from the 8V Alfa 33 series 2 QV workshop manual.

The left bank is when you sit in the car, drivers seat, facing forward, the 2 cylinders on the left of the car.

[Brit01]

The left bank is when you sit in the car, drivers seat, facing forward, the 2 cylinders on the left of the car.

Thanks Whizzman. That's what I was thinking but just wanted a confirmation/second opinion.

[Guy Croft]

That's the F1 convention too, very confusing when you first encounter it as I did all those years ago at Brian Hart'sworks.

I'd like to meet the guy who came up with that potty idea, considering that the entire build of every engine on the planet is 'set off' from - or relative to - the crank nose.

G

[WhizzMan]

The logic stems from agreeing on what the left side of the car is and staying with that throughout the entire car. It'd be kind of odd to talk about a left front fender being next to the right engine bank. At least with Alfa Romeo, this is the convention they keep.

[Brit01]

whizzman/Guy:

You really need to deglaze your bores, or your new rings won't bed in

If I take a good close up photo of the surface of the bores would you be able to tell if they need a proper de-glaze or just a good clean with carb cleaner and scotch pad?

For me they look ok but a second opinion is always good.

I have seen de-glaze attachments for drills that can be done with the block in the car.

thank you

[Guy Croft]

left side of the car is and staying with that throughout the entire car. It'd be kind of odd to talk about a left front fender being next to the right engine bank

Kinda makes sense I guess..1

G

[Guy Croft]

Rings - if they are still with their associated pistons put them back in their original bores with gaps set at 120 deg apart.

Just clean the bores with brake cleaner and oil them lightly.

If you have new rings that's another matter altogether. No way may you hone by any means in-situ.

G

[WhizzMan]

Flex-hone can be used in a hand drill.

You really need to hone outside of the car because you need a straight angle for the flex to be moved up and down the bore. Also, you need to clean out the debris after honing and you can't do that properly with the cylinders horizontal. Most important, you need to be able to measure up your bores before you do anything. It's no use honing an oval cylinder that won't fit your pistons anymore.

[Guy Croft]

Quite a lot on this at:

viewforum.php?f=3

G

[Brit01]

It's no use honing an oval cylinder that won't fit your pistons anymore.

Pretty sure my bores are in very good condition. They were honed just 18,000 kms ago.
I did a compression test before taking out the pistons and have 190 psi on average for each cylinder.

I will give the bores a good scrub and inspect the cross hatch and surface carefully.

Quite a lot on this at:

viewforum.php?f=3

G

Thanks Guy. I'll read through these.

If they are in good condition I could always use a scotch pad attachment on a drill.

(link deleted by GC - under Protocols links are not permitted without my specific authorisation by pm or email. I am notsure I have refused many (if any) but I wish to see first)