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Author: Subject: MX5 mk3 engine rebuild or replace
cliftyhanger

posted on 15/9/23 at 08:09 AM Reply With Quote
MX5 mk3 engine rebuild or replace

Daughters MX5 mk3 1800 has developed what appears to be a big end knock.
And so after my holiday I have no doubt it will appear on my drive. (My dolomite drivetrain swap to sprint running gear will be push down the queue)

I haven't got a clue if I can inspect the big ends in situ. I suspect dropping the sump will be a ball ache? Anybody got experience?

If it is just a big end (rather optimistic) I will replace if the crank is OK. If not, or it has spun the bearing, I will have the choice of possibly a replacement rod/piston, replacing or regrinding the crank, a bore hone and new rings. While in teher some new valve stem seals which have been iffy since she bought the car.

The alternative is another used engine. Is the ford version a (more or less) straight swap? I worry it may not be much better than the old one though. MX5 1800 engines seem to fetch serious money.

All this on a car that is worth about 2k. But she really likes the car....

Advice very welcome

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nick205

posted on 15/9/23 at 10:44 AM Reply With Quote
Spending too much time and money on a car that's not worth a great deal (and won't be increased in value by doing so) is an expensive and weekend eating task.

She may like the car, but they're not rare things are they!

Personally I'd be inclined to move it on and look for another.

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theconrodkid

posted on 15/9/23 at 11:59 AM Reply With Quote
i am sure i read somewhere you cant get internals for that engine so best to slap a good used lump in ?





555

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cliftyhanger

posted on 15/9/23 at 01:27 PM Reply With Quote
Re parts, rings are available in std size. Bearings as std, +,25 and +.50 so that stuff ius covered. I think you have to fit a complete piston/conrod assembly, but there seems there are people supplying good used parts.

Re costs, if it can be sorted for under 1k plus a few days, it will be worth doing. Having asked about, any MX5 of that era can have the same issues at any time. Refreshing the engine should mean it is good for several more years, and should add tho the value should she sell it. Probably.

My main issue is that info is hard to come by.

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40inches

posted on 15/9/23 at 05:34 PM Reply With Quote
I take it you have tried MX5Nutz for info?
If not they are here: https://www.mx5nutz.com/forums/

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perksy

posted on 15/9/23 at 11:30 PM Reply With Quote
Sadly quite a few have succomed to this on both the 1.8 and 2.0 engines in these

Can't remember if you can drop the sump and check (with the engine still in the car) but I think there's an issue because of the crossmember being in the way?

Think the general consensus was to swap the engine for a known good one, BUT with these engines I think I'd be wanting to hear it run first before fitting it...

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JC

posted on 16/9/23 at 05:23 AM Reply With Quote
Check underneath for rust before you commit to open engine surgery…….,..
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cliftyhanger

posted on 16/9/23 at 07:40 AM Reply With Quote
quote:
Originally posted by JC
Check underneath for rust before you commit to open engine surgery…….,..


I have. It is very good, apart from the rear of both inner sills that I cut out/welded up last year.

Re the engine, that is teh issue. A "good runner" is going to be about £1k, maybe a little less. But once the engine is out, a rebuild is pretty straightforward and a safer bet I reckon. The engine in teh car felt good and strong when I last drove it recently.

Part of the issue is probably the oil pressure gauge. Which doesn't read the oil presure at all! it calculates it from RPM and temperature, so useless.

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