Rust on cylinder bores common after standing?

[acealfa]

Hi,

Just stripped down a diesel engine that's been standing for about 4 months and there's some rust patches on cylinders 1 & 4. I have tried to remove with WD40 and scotch pad but I'm not sure if it's best to take out the pistons and hone the bores?

[GreenV8S]

As long as there's no pitting I expect it'll be fine. It's quote common for rings to rust to the bores so badly that the engine won't even turn over. To prevent that you'd tip a squirt of oil into each cylinder and turn the engine over a couple of times before a long layup. Too late for that now in your case, of course.

[NMNeil]

Fairly common that condensation will cause surface rusting after standing for a while, but looking at the photo you have quite the wear ridge at the top of the cylinder. Honing won't shift that.

[acealfa]

NMNeil said:

Fairly common that condensation will cause surface rusting after standing for a while, but looking at the photo you have quite the wear ridge at the top of the cylinder. Honing won't shift that.

Do you mean above the line?

[E-bmw]

acealfa said:

NMNeil said:

Fairly common that condensation will cause surface rusting after standing for a while, but looking at the photo you have quite the wear ridge at the top of the cylinder. Honing won't shift that.

Do you mean above the line?

No, he means the line itself, there shouldn't be one.

There is also what looks like some slight pitting towards the upper reaches of the swept area of the bore.

[acealfa]

The line is basically the top of the stroke for the top piston ring, above that was just carbon build up before I cleaned it so didn't think anything of it. I'll have a closer inspection. I replaced the rings even though the olds ones seemed ok. The original fault was failed turbo & blow by through valves.

[gazza285]

If you are fitting new rings then you need to have the wear ridge removed, you old rings have worn that, as well as themselves, your new rings will hit that and break.

[acealfa]

gazza285 said:

If you are fitting new rings then you need to have the wear ridge removed, you old rings have worn that, as well as themselves, your new rings will hit that and break.

Thanks for the information, I'll get that done.

[NMNeil]

E-bmw said:

acealfa said:

NMNeil said:

Fairly common that condensation will cause surface rusting after standing for a while, but looking at the photo you have quite the wear ridge at the top of the cylinder. Honing won't shift that.

Do you mean above the line?

No, he means the line itself, there shouldn't be one.

There is also what looks like some slight pitting towards the upper reaches of the swept area of the bore.

And looking at the piston the gaps on the left and right are larger than the gap at the top possibly indicating a worn and oval bore.

[dontlookdown]

acealfa said:

gazza285 said:

If you are fitting new rings then you need to have the wear ridge removed, you old rings have worn that, as well as themselves, your new rings will hit that and break.

Thanks for the information, I'll get that done.

Or you could fit a set of step Dodger/top hat upper rings and just hone the bores. Depends how much it's worth spending on the car, and/or how much work the OP wants to do.

[Pete54]

You really need to measure the bores - especially if you are going to hone them. If you increase the running clearances of the pistons beyond the normal limits whatever work you put in will be short lived.

That may not be a problem - if you only want it to run for a short time. If it is a keeper that is another matter. The bores look worn and there is that fairly obvious wear ring at the top of the pistons' travel. If the bores are worn beyond the normal running clearanes then new rings, even with the modified top ring step, will not last long.

[acealfa]

It’s not a keeper but i’d like to do it properly. The knowledge I’m gaining along the way is golden & why I started it. I’m going to buy a bore gauge & take it from there. I appreciate the advice.

[stevieturbo]

It will be best to take pistons out and hone the bores.

But any deep rust, you will likely never get them out with a hone anyway.

If it's just something you need put back together, running and gone, quick ball flex hone and send it on it's way. It'll maybe burn a bit of oil, but it's a smelly oil burner anyway.

[acealfa]

I've not done anymore work to it yet but have some questions that don't necessarily relate to me but in general ..

If the ridge was reamed out & the same pistons used would this cause an issue as the gap would be bigger around the piston? & if so would the best practice to be to ream 1-2mm above the line only.

[chrisch77]

acealfa said:

I've not done anymore work to it yet but have some questions that don't necessarily relate to me but in general ..

If the ridge was reamed out & the same pistons used would this cause an issue as the gap would be bigger around the piston? & if so would the best practice to be to ream 1-2mm above the line only.

You can't just 'ream' to a depth to remove the step at the top of the bore. Apart from anything else the actual wear is probably not perfectly round so you can't match that with machining at the top of the bore.

As noted already, you need to measure what the wear is in the bore and determine how big the step really is. If the step is significant then the clearances will also be too big for the existing pistons, so anything you are considering will just be a short term bodge without going for a full honing or worst case rebore and new pistons.

If you really don't want to do anything with the block then the safest plan IMO would be to keep the old 'top' rings and not fit new ones, so they match the existing shape of the cylinder step.

[NMNeil]

Honing removes metal and this engine needs metal added not taken away.

[acealfa]

chrisch77 said:

You can't just 'ream' to a depth to remove the step at the top of the bore. Apart from anything else the actual wear is probably not perfectly round so you can't match that with machining at the top of the bore.

As noted already, you need to measure what the wear is in the bore and determine how big the step really is. If the step is significant then the clearances will also be too big for the existing pistons, so anything you are considering will just be a short term bodge without going for a full honing or worst case rebore and new pistons.

If you really don't want to do anything with the block then the safest plan IMO would be to keep the old 'top' rings and not fit new ones, so they match the existing shape of the cylinder step.

I've ordered a bore gauge so I'll take proper measurements once it arrives. That's a good tip I will bare in mind for the future, unfortunately threw away the old rings already, d'oh.

[NMNeil]

acealfa said:

I've ordered a bore gauge so I'll take proper measurements once it arrives. That's a good tip I will bare in mind for the future, unfortunately threw away the old rings already, d'oh.

You don't say what the engine is, other than a diesel. Looking at the photo again it may have pressed in sleeves or liners, which can be replaced fairly easily, and enable you to reuse the old pistons if they aren't too worn.

[stevieturbo]

Stop wasting time and money.

Give it a quick hone and "send it" on it's way, minimal new parts and spend. No doubt it will run just fine for many many miles

Or take it all apart and do the job properly with bore/new pistons etc.

Measuring bores isn't going to tell you anything of value.

[acealfa]

I like the that reply

That’s what I’ll do but I am intrigued to see how worn they are.