How many km did this engine run ?

Mon Oct 22, 2012 10:54 pm

Hi i bought an m20b28 engine with 0km (new built).

After 1500 km "run-in", i began to push it more and had an head damage.

Now im disassembling the engine. I took the cylinder head off today. An it looks so:

Is it possible that this engine only ran about 2000 km ?
Im courious about that because of the amount of carbon and dirt on the pistons and head. Or is this normal ??

Then the scratces in the bores ? What could be the reason for them ?
Could they be caused because of water in oil and less lubrication ?

Or was the engine built up wrong somehow ?
Maybe wrong or old piston rings ?

Im not an engine expert (opend an engine first time) so need some help, what could cause such damage ?
In addition: i had no piston squeezing, i drove the car in my garage and turned it off.

Thx

Mon Oct 22, 2012 11:32 pm

Well its hard to say about the carbon on the pistons and combustion chambers because of so many factors which could cause it, but I'll tell you what I think.

The engine was almost certainly burning a bit of oil, because there are little or no honing marks left in the bores, this is because the block does not look as though it was rehoned during the rebuild. The honing marks hold a minute amount of oil that lubricates the piston and rings, and seals the bore, a smooth finish like you have in the pictures cannot do this, they burn oil and lose compression.

The vertical scoring is almost certainly from the engines previous life as a H/C M20B25 by the looks of it, something has been in there, foreign body, carbon particals, not sure but the should not have been pressed into service without sorting this damage. Blocks are cheap so no excuse.

It is not cheap to build the bottom end of these, and i'm sure it would be tempting for some to cut corners and just put a m52 crank in an m20 and call it a full rebuild.

Its hard to give a diagnosis with a few pictures, but if I opened an engine after 2000km I would expect to see honing marks, and no cylinder wall damage.

What made you take it apart?

Wed Oct 24, 2012 9:15 pm

After 1500 km "run-in", i began to push it more and had an head damage

what was the head damage ??

and if thats a new build engine im the queen of england

Wed Oct 24, 2012 9:27 pm

That looks like NO CARE was taken when rebuilding the engine,

And Ross, I bet you look good in the Royal Gown

Sat Oct 27, 2012 10:04 pm

maggspower wrote:Well its hard to say about the carbon on the pistons and combustion chambers because of so many factors which could cause it, but I'll tell you what I think.

The engine was almost certainly burning a bit of oil, because there are little or no honing marks left in the bores, this is because the block does not look as though it was rehoned during the rebuild. The honing marks hold a minute amount of oil that lubricates the piston and rings, and seals the bore, a smooth finish like you have in the pictures cannot do this, they burn oil and lose compression.

The vertical scoring is almost certainly from the engines previous life as a H/C M20B25 by the looks of it, something has been in there, foreign body, carbon particals, not sure but the should not have been pressed into service without sorting this damage. Blocks are cheap so no excuse.

It is not cheap to build the bottom end of these, and i'm sure it would be tempting for some to cut corners and just put a m52 crank in an m20 and call it a full rebuild.

Its hard to give a diagnosis with a few pictures, but if I opened an engine after 2000km I would expect to see honing marks, and no cylinder wall damage.

What made you take it apart?

Hmm, What he said.

The bores certainly look a bit shiny for such a fresh motor and the scoring is certainly a sign of some kind of interference with the bore, be it from foreign object or an issue with the rings.

Tear it down and take a good look, something is wrong there.

Sat Oct 27, 2012 10:31 pm

The Reason why i took the head of was mixing of water and oil. While this test run (just after 1500km run in and oil change) where i tested first time full throttle the low water light went on.
Then i filled it up and while driving home (60 Miles) the engine consumed 1 L Water.

Test run:

Here some pics of that:

I thought the head was cracked and caused the mixing, but the head looks good for now. Camshaft is still in, but can´t see any cracks, maybe when i pull it.

However the block has a crack. Look here:

This is surely a reason for mixing oil with water. So now i hope the head is ok and i can use it for the next engine.