Peening k series cylinder heads

[rrobson]

Read about this on another forum so i thought id try it on a spare head i had at home.
dont know how sucsessful this technique is but we will soon find out!
heres what i did anyway, just incase anyones interested

completely stripped the head ready for machining



as you can see, the gasket has made a deep impression where the metal has softened.





only the exhaust side has really been affected as the inlet side was still as hard as required

so i set about hitting the head with a big hammer...







note the difference in size between the peening marks. the large ones are obviously where the metal was soft. the same touch was used around the fire ring.





really annoying as the largest cutter we have is 1/4" too small! took them bits off after though.

this is the second time ive skimmed this head and from what i can gather its the third time in total. ive only taken 8 thou off this time an took 13 thou last time so next to nothing. the problem is when workshops remove loads of material unnecessarily. i have taken the absolute minimum off.
theres still enough material for another skim, so that would be 4 skims. if id have had it from new, i recon there would be room for 5 skims before its scrap. could always skim more and use a thinker gasket shim.

[mh007]

Blimey, I haven't seen that technique for a while !

We used to do this quite a lot on the older cars with ally heads.

With gasket technology moving forward, I haven't done this for ages.

I always use a MLS gasket on the K series now & that seems to do the job well (head always skimmed of course)

[Talago]

I thought the K series heads were 'case hardened' (if that is the right term) so skimming them leaves the visible surface softer than before.

[mh007]

I can see this post going down the 'To skim or not to skim' route again !

[rrobson]

yeah, thats what the peenings for. it work hardens the metal below the peen therefore making it harder.

half of the ring was VERY soft though, so i wanted to see if it could be saved.
as said, not as critical now, especially as the saver shim is used with a mls gasket, but if it needs skimimg, it may as well be peened as well

[James.uk]

The original heads were machined with cutters that had a negative rake, so they were burnished at the same time. That gave them a harder surface and closed off any porous areas.

Machining with a "blunt" cutter tends to push material along, a bit like spreading butter..

I take it you used a mill cutter rather than a surface grinder due to the risk of clogging up the grinding wheel Reece?
...

[rrobson]

yes james. we dont have cutters anywhere big enough with negative rake to do it. i think youve put that somewhere else, im sure ive read it before.

i used a finishing cutter, and the finish is spotless. you cant feel the cutting marks but you can see them. gave it a good rub down with some polishing paste to help shine it up too, so it is better than in the final pic.

problem with burnishing is you need a very high spindle speed and we cant achieve anywhere near whats required. maybe on one of the cnc machines bt not on a conventional miller.
i could have used a fly cutter, but i would have been there all day to get the finish.

and i wouldnt touch a head with a grinder, it would ruin the wheel... weve only got fine wheels so theyd clog up straight away

[rrobson]

for those that were interested, this technique has worked, and made the fire rings harder.
i know this because the head had to come off again once fitted (problem with gasket, another story) and there were no indentations left what so ever.

so id say soft heads can be salvaged