NB8A blown head gasket

wydra · Postby **wydra** » Tue Mar 04, 2014 11:53 pm

Hi guys,

On a highway drive down south on a warm weekend the bottom radiator hose blew off (the BEGI pipe they supplied didn't have a suitable lip and was badly powder coated) and the engine got hot. I shut it down as soon as I saw the temp going up but it obviously still got too hot and the head gasket is gone, possibly more. As I was still many km's from home I had to do a road side fix (not fun), fill it back up with coolant and baby it home. When about 20km from home I noticed a misfire had developed and when I finally got home bubbles in the overflow tank.
This afternoon I compression tested the engine just to see and it isn't looking good... one of the cylinders down to 60psi, 2 of the others not brilliant.

So now time to fix this mess.

Usually for this type of fix I would go for a Genuine OEM head gasket from Mazda. Can anyone recommend against this and/or is there a better option out there?

For the head bolts, is there any benefit for going to ARP head studs? or will a new set of Genuine OEM bolts do the job fine or might I be able to get away with the old ones? What are peoples experiences?

I wont know if the head is OK/cracked/warped until I pull it off later this week.
If the head is serviceable and the bottom end still looks ok when I get the head off, is there anything else worth doing while I have the head off? I just changed the timing belt, seals and water pump about 1000km ago.

Obviously if the bottom end is buggered or if the head is cracked I'll have to look for a new engine but for now I'll hope towards fixing this one.

Thanks,
Dale

Postby **Okibi** » Wed Mar 05, 2014 12:10 am

That sux Dale :frown:

Keen to see everyone's suggestions too.

geofiz · Postby **geofiz** » Wed Mar 05, 2014 12:38 am

Headgasket is around $35.
Head bolt set around $30.
Plus shipping from US looks like around $70.

Measure the old bolts, if they haven't stretched too much should be fine for a re-use.

Depends on how hot the engine really got.

If time is not critical, grab some ARP bolts. Let me know if you get stuck for time, I have some spares you can use and replace at a later date.

Russell.

Postby **Okibi** » Wed Mar 05, 2014 1:10 am

Russ you're a credit to the MX-5 community :mrgreen:

wydra · Postby **wydra** » Wed Mar 05, 2014 1:32 am

Thanks Russell,

Are those prices for Genuine OEM sets? where abouts in the US are they from?
I was looking on mx5 parts in the UK and they were a fair amount more than that.

As for the ARP head studs, where did you get yours from? did you get studs or bolts?
If I can get a set quick enough (same time as the head gasket etc) I might go down that path.

and1 · Postby **and1** » Wed Mar 05, 2014 2:18 am

I got mine recently from Rosenthal Mazda in the US. Mainly because MX5Parts.uk didn't have listed what I required, so I bought the whole lot from Rosenthal.

I can dig up total cost if you'd like...

project.r.racing · Postby **project.r.racing** » Wed Mar 05, 2014 10:34 am

i'd be more included in finding the issues caused from overheating first before worrying about parts. it could have a alloy head the shape of a banana right now.

wydra · Postby **wydra** » Wed Mar 05, 2014 10:40 am

and1, that would be great.

project.r.racing, I might as well get the parts on the way before I make a start. For the cost of a head gasket and some bolts its worth it and I'm going to use them one day regardless.

droo · Postby **droo** » Wed Mar 05, 2014 10:41 am

With the head overheating, when you remove the head, you will want to get a hardness check done at a reco/machining shop - takes about 2 minutes for them to perform the bearing drop tests around the combustion chambers. Many will do it there and then and won't charge you anything for the check. If the metal is soft, they'd recommend getting a replacement head - as there's no reasonable way to harden it up again.
Replacing it back into the car with the soft metal will mean it will continue to blow past the gasket in a short time…

(My previous head i had overheated after blowing the gasket at around cylinder 3, the alloy was very soft there in the head - the bearing test clearly showed that. Gasket failure also from coolant/radiator issues)

If all is well tho, get it shaved 20thou, (increase compression a smidge, save weight a smidge, pfft lolz), and it will be a flat machined surface ready to be installed again.
With the head shave, i had read on various roadster forums i'd encounter issues with timing belt alignment, yet mine has aligned nicely and isn't out - at least i couldn't see it out by any noticeable amount visually..

I got my roadster's head done; a multi angle valve cut job thingy, port matched intake/exhaust and some other stuff for under $900 in october 2011.

johnnyreble · Postby **johnnyreble** » Wed Mar 05, 2014 11:15 am

Shaving the head shouldn't alter the timing at all as the belt tensioner will take up the play.

droo · Postby **droo** » Wed Mar 05, 2014 11:41 am

thats exactly what i noticed.. Just mentioned that as i'd read conflicting all sorts and stuff on the forums..

Postby **NitroDann** » Wed Mar 05, 2014 12:02 pm

Wrong. Shaving the head affects cam timing.

When you tighten the tensioner as required it pulls the tops of the cam gears left because that's the side the tensioner is on.

To rectify this either fit adjustable cam gears and use them, or for much cheaper simply fit a second tensioner where the other idler would go on the other side and tension them both evenly.

A head shave in most cases won't affect can timing enough to worry me, unless its a high budget competition build.

Dann