Mild or severe knock

Hi,

Appears that I'm planning on reusing some parts of an engine that has suffered knock to a certain amount leading to a sudden and very high oil consumption, and then lots of burnt oil into combustion chambers and valves.

I know why, that's not the question, and the problem has been addressed since then, but what I'm struggling to define is whether or not it's ok for me to reuse these parts.

I only need to reuse bare block (cast iron) and fully equipped head (aluminium).

Engine block seems ok so no question here, but as you may think, head's squish pads shows pitting marks (pistons has been quite badly damaged).

I'd like to define if it's safe for me to reuse this head (knowing that it'll be decked around 0.01mm, depending on some decisions I still have to make as per desired CR), but I don't know how...

My concerns are about the heat treatment of the head, something I'd never heard about before I have to admit, and also the condition of the exhausts valves.

- How can I be sure that the head is fine heat treatment wise? Is there any colour patch or something I should look after?

- Valves aren't perfectly oil tight when I try them, but I enhanced this quite significantly just using some brake cleaner and a clean rag, so I would assume that this can be corrected quite easily by a machinist. What you think? Is there a potential for problem with heat treatment here? I do have spare valves at my disposal but I'd like to avoid having to change valve seats for several reasons.

Of course, if needed I can provide good quality and close up pictures of anything here, shoud it help!

FYI:

Block is from a 2003 Mazda Mx5 2003 BP6D 4 cylinder 1.8l engine (cast iron) that will be rebored to 84mm (+1mm from stock) in order to fit a set of Wiseco forged pistons (K590M84 kit, high comp set), to be fitted with a 1999 Mx5 BP4W head that has already been skimmed for previous use and ported by a professionnal, and otherwise than the exhintake, will be used with stock specifications. Aiming for around 11:1 CR, N/A engine obviously.

Use is only street and amateur track days, so no big power and no big stress onto the engine to be expected, then it's possible for me to work for something that is not perfect as long as it still not causing problems and shows normal reliability.

Head squareness and water / air tightness will indeed be controled by machinist after I'll have also performed my own controls and measurement (not my first time).

Can you please help me taking a decision on this matter?

To me it comes down to all regular measurements that need to be done when assembling an engine. If head is warped it needs to be grinded, if valves are bent they need to be replaced. Valve guide clearances also to be checked. Nothing fancy but old good routine checkes... Should not be hard to complete.

The machine shop should be able to hardness test the head, it's a simple check and often done as a matter of course by good shops.

You should be fine with a light skim, depending on the damage, but you'll need a lot more than 0.01mm as that's less than a half thou' ;-)

You mention the head has been skimmed previously, so it'd be a good idea to do a V2P clearance check, after the additional skim.

Hi all!

Sorry, was out of gold membership at the time, which allowed me to "resolve" the thread but not to answer on it.

Didn't want to look rude...

Anyways, I'm still not finished with this engine. Bare bloc is still at the machinist's to be rebored.

Head has already been fully controlled, measured, and skimmed (0.1mm, there was indeed a typing mistake that posted one extra zero).

This was not sufficient enough to completely erase the piting where it was deeper, but after talking with some other people at the time (including the machinist who did the skim and a friend who built like 40 - 50 various cars and bikes engines during the last past 20 years), this was not a real problem plus there is no OEM heat treatment on these heads whatsoever, so no big deal.

Valves and seats have been corrected too, still have to do some finishing on this part because it appears that valves are not fully adjusted (oil tight but not petrol tight...). After discussing it furthermore with another machinist, it seems that they all do that: just correct valve and seats barely, don't do any finishing because that would take too much time that they don't want to charge you in order to stay competitive, and then tell you not to do any finishing because "it's not necessary", but in reality it's more like they don't want you to realize that the work is not finished not to be shown off.

Then I've been strongly advised to do it anyway by this other machinist who I trust more, so... will undo the valves again and do the finishing paste / suction cup thing that I thought they did.

And btw, when I posted this thread I estimated the target CR based on bad memories I had about what was the current CR with this head.

Real digits, confirmed after combustion chambers volume measurement, are more like 12:1 . Should be interesting given the fact I planned to make this engine run on E85 anyways!

Here is the whole story then.

Can't wait to have this running, hopefully before July but still accumulating unplanned delays so not looking good unfortunately.

Thanks again for your help anyways.