Blown head gasket. Which way to go?

[lonesailor]

I blew a heater hose on my NA8 the other day. Car was running fine and fast when I noticed the temp. guage way over the top. I shut down as soon as possible 4-500 metres later and had the car towed home. Replaced hoses, refilled coolant, started OK but has a bad miss, and steam from the exaust, Diagnosis blown head gasket. My decision now is what to do, seeking opinions. I have had the car 26 months, hane done 35,000 km.as second (toy) car. She has 240,000 km on the clock and is in very good nick.I haven't much info on it's history but believe it sat unused for some years before being tidied up for sale, which has been well done. I was assured it had had the timing belt replaced at around 200k.Don't know about waterpump.
My decision now is. Do I just pull the head, check surfaces are true, inspect the timing belt , bore condition etc., replace if required and reassemble, or pull the engine, strip it, check everything is within tolerances, check clutch and replace if indicated, do waterpump and timing belt and seals and bring engine back to "as new" condition?
What do others think? I'm not too flush with funds, but do have alternate transport. What is the expected life of engine internals,clutch,waterpump etc. given my age and use of the car I would expect to have 5 years and about 100,000k left in me, what I certainly DON"T want is to spend a lot of time, money and effort on her now only to have to do it all again ( or,by then,have to have someone else do it). Opinions requested

[The American]

When the head gasket went on my na8, the bill for parts, machine work and labour would have been comparable to the price of a secondhand low km engine. My engine was younger than yours - 170k - and so I thought it was worth it to stick with what I had rather than an unknown engine. In your case, if you are looking for another 100k, it could be worth checking if any of the mx-5 specialists have an NA8 engine in good nick.

[93_Clubman]

blew a heater hose on my NA8. noticed the temp guage way over the top. shut down as soon as possible 4-500 metres later and had the car towed home. Replaced hoses, refilled coolant, started OK but has a bad miss, and steam from the exhaust. Diagnosis blown head gasket. has 240,000 km on the clock and is in very good nick. assured it had had the timing belt replaced at around 200k.Don't know about waterpump.
not too flush with funds, but do have alternate transport. What is the expected life of engine internals, clutch, waterpump etc. given my age and use of the car I would expect to have 5 years and about 100,000k left in me

BP (1.8 ) motor is fairly bullet proof & there are B6 (1.6) motors on here with close to half a million kms. Given all the above, do the bare minimum, especially if you're not doing all or most the work yourself. Even if you are doing all or most the work yourself, still do the bare minimum.

[bruce]

An observation; 35,000 kays in 26 months as a toy car, is a lot of kays.

[OMY005]

check clutch and replace if indicated, do waterpump and timing belt and seals and bring engine back to "as new" condition?

Do the cam belt and water pump (cam seals, front and rear crank seals) while the head is off. Might as well do clutch plate and spigot bearing.

Andrew.

[Mr Morlock]

Probably for any car with similiar kilometres. Remove the head , resurface new headgasket and refit. Cost $? If the engine was not using oil and running ok then leave it be. Pulling engines apart and getting bores done etc etc costs costs $$- that is the way of the world- labour / overheads too high. Bear in mind this could be quite a cheap repair. Just do the $ numbers.

[bootz]

It is quite possible with these Mazda engines that you have cooked the head permanently. The metal becomes soft and cannot be relied on. In that case a new head will be necessary.

[greenMachine]

Pull the head yourself. Do a hardness test. If ok, just do the head gasket (not a full overhaul), leave the valves unless they are too bad.

New head gasket (get the right one), skim the head plus water pump/idler pulleys (if the water pump wasn't changed, the idler pulleys probably weren't either), plus gasket set, and you are good to go. Rustle up a few mates, a bit of googling and a torque wrench and a few sockets and you are going again - for very little money These are pretty straight forward engines, there are a couple of tricks and you need to get the timing right, but very doable for a novice working with care and a bit of help.

Clutch is a much bigger job, not to be contemplated short of a failing clutch or the engine being out for other reasons.

There are no guarantees, but that is likely to last you 100,000 kms. The risk is that either the head is soft (which if you have it tested can be identified before you have spent a lot of money), or the rings are gone and it starts using oil when re-assembled (probably no sure way of telling unless you remove and strip the engine), but you pays your money and makes your choice.

Good luck.

[StanTheMan]

Why would you not toch the valves? Unneccecary expense? Too hard? To complicated?

[lonesailor]

Have removed the head over the weekend, it has a .010" warp, had a hardness test done this morning and it's soft. I need another head. Does anyone know if any other Mazda vehicles have the BP05-11-2 head so I can try for a secondhand one?

[greenMachine]

Good question Stan. I was describing a minimalist (lowest cost/effort) repair, rather than a rebuild. I think valves are a judgement call, based on the evidence.

It's a slippery slope. When you start on these high km engines, where do you stop?

In this case, I would pull the engine, check the head hasn't gone soft, and if it was ok, do a full rings and bearings overhaul, with a new clutch/TOB, regrind the valves, and know it was good for another two or three hundred thousand kms. If the head is soft, put in the lowest km second hand engine I could find, and hope for the best - these are a gamble, but the odds are pretty good (especially if the engine came with a warranty).

But that is just me. From the OP's post it didn't seem he wanted a full overhaul, so I went to the other extreme with the simplest solution to the problem. Apart from the valves question, the other unknown is the rings, and how they held up to the overheat event. Because I am comfortable working on these engines, I would go down the full rebuild route just to be sure the rings did not give me any trouble.

[greenMachine]

Have removed the head over the weekend, it has a .010" warp, had a hardness test done this morning and it's soft. I need another head. Does anyone know if any other Mazda vehicles have the BP05-11-2 head so I can try for a secondhand one?

Bummer!

I don't know the answer to that. But my observation is that heads are scarcer than full (second hand) engines, and I suggest that you scout out both options.



ETA: If you do get a head, make the purchase subject to a hardness test

[93_Clubman]

Does anyone know if any other Mazda vehicles have the BP05-11-2 head so I can try for a secondhand one?

Yeah, BP motor of that vintage used a variety of BP05 heads & cams in the various Mazda 323 & MX5, including a variety of BP05 heads in the MX5 NA8. The BP4W head of the NB8A is the scarce & expensive one, whereas the BP05 bare head can be picked up for $100 pending hardness test of course. MX5 head identifierS: NA8: BP05; NB8A: BP4W; NB8B & NB8C: BP6D; NB8D SE: BP4W.
Here's examples of the variety of BP05 heads found in the NA8:
viewtopic.php?f=44&t=70346&hilit=bp05
viewtopic.php?f=44&t=67759
viewtopic.php?f=44&t=72858&hilit=bp05

[manga_blue]

The BP4W head bolts onto the NA8 block and is a much better performing head than the BP05. You must use the BP4W cams and buckets as well. You'll need to transfer all the NA8 sensors and cam cover across to it. The NA8 manifold mounting bolt hole pattern is different. The best and fastest option is to get a BP05 to BP4W manifold adaptor plate from Danstig Engineering on ebay.co.uk. This gives much better power and torque spread than the BP4W manifold and does not require switching to operate the BP4W VICS variable intake system.

x4 on hardness testing anything you use.

[NitroDann]

Everything manga said.

110%.

Dann