Lost compression - How much on a rebuild kit?

[mctaggart]

My Mercury 1999 75hp 2 stroke with oil injection has suffered some kind of failure which has caused damage to my engine. I had compression tested it 3 days ago and all three cylinders had a healthy 130psi each.

While out at sea the engine died suddenly for no reason but started back up ok, on the way back it happened again and for some reason if i went over 15knots the engine would cut out.

On the 3rd restart the engine was now missing on one cylinder and we limped back on two cylinders to the dock.

I have had the engineer call me today saying that he compression tested it and it now has

80psi
32psi
80psi

So somehow its killed its self, he noted he couldnt see any blue smoke coming from it especially when starting cold and suspect possibly its not been injecting oil. I am gutted

Engine was mint now its bloody fooked and i expect a big repair bill. I am just preying the damage to the powerhead isnt so bad that its scrap and can be at least bored oversize if need be.

Can anyone give me prices on a engine rebuild kit for a Mercury 1999 two stroke 75hp (Red stripe top). May as well overhaul the whole thing.

The engineer has recommended that we bin the oil injection system and go premix in future, they do all the RNLI boats and he told me thats the first thing they do, they dont even bother using the oilers as its a REALLY expensive repair if they ever fail and are not worth the risk, more so in an older engine.

luckily this guy is not expensive and does alot of the local fishermens boats, he said £100 at this point to tear the powerhead down into its parts and find out what the damage is, i am praying its not completly shagged!

[Nos4r2]

With 80/32/80 compression I reckon you've had an oiling failure too.

I'd change the powerhead. At the least you're going to need rebore+pistons on each cylinder, but quite possibly some new bearings too.

[mctaggart]

Yeah its gone from 130psi 3 days ago then down to 80,32,80!

A new powerhead would no doubt be ridiculous money i noted they do oversize pistons on these and rebores are cheap as chips.

I eagerly await the report tomorrow, brown pants time!

[Boats&Outboards]

Sounds like there's more to this than meets the eye. Didn't you report problems recently on this ? were they not resolved before going back out ?

Like Nos said I'd swap the powerhead. As it happens, I think I had posted one up here not that long ago which was available through a contact, brand new over-stocked powerhead (including all internals but no exteriors carbs etc so you'd still need to check into the oil system). It'll be a drop on replacement, although it's 90hp model (same block)

Would you like me to check If it's still available ?

Peter @ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

[mctaggart]

Yeah it was running lumpy when i had it and sneezing, it blew off the fuel pump pipe and i had replaced it with a new one, I had also linked and Synced the carbs after this happened and it seemed to fix the original problem of it sneezing. It ran fine for about 6hrs use after this so i think its unrelated.

Yes please can you get me a price on the block?

[Boats&Outboards]

It won't be cheap as its new/unused but it's a better option than a re-build IMO. Update when you know the situation and I'll check it's availability and let you know.

Peter @ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007

[uncle al]

if you are going to rebuild your p/head and want it rebored as it will be what they call a blind bore it can be expensive, if it is any help if you go down the rebore route they dont all have to be the same size bore as all the pistons are the same weight, but spares will probally be expensive , and a new p/head would be better (cheaper)if you keep the oil injection please have a good look at it and dont re-fit a (for example a dodgy oil pump) if you want to pm me and i will go into it further if you want me to

[mctaggart]

Well I have a good engineer for the workshop part so I don't think the machine side will be that expensive. How much should I expect to pay for a new power head?

[uncle al]

I am sorry I dont know prices ,I only know how to fix them I used to work for the distributer so nearly all the repairs that i did came under the warranty banner.it might be worth giving Robby at Blackdog marine either a ring or a pm he is on this site

[mctaggart]

I just mentioned to the machine shop its a blind bore, so he said he won't know if their machine will reach it until they look at it, dam oh well !

[uncle al]

we used to send our cyl blocks to F.J.payne they are at enysham in Oxfordshire if that is any help I dont know the phone number and havent got a directory

[uncle al]

I have just googled fjpayne their phone number is 01865 882299

[mctaggart]

Just spoke to engineer, piston 2 is toast with heavy damage to the bore, so a resleeve is required at least or he has got a spare 2nd hand block. Luckily the crank is fine as well as the other two pistons, so I only need new bearings, one piston, and a set of rings. So it could have been worse! But it was an oil starvation problem. Anyone know what the going rate is for a 2nd hand 75hp power head or a resleeve on one cylinder.

[buzzin hornet]

Sorry to hear your engine woes.. How easy is it to disconnect the autolube system. Ive been told previously to go premix but have never acted on it. I suppose you only find out you have an oiling problem when the engine fails.

Good luck with getting the engine sorted

Buzzin

[9D280]

I thought I might have been in a similar situation when mine died. I decided on the rebuild route becuase I now have a known quantity as opposed to a secondhand unknown quantity of unknown history for the same cost that may or may not go bang.....

Mallory Pistons as you say - cheap as chips. I assume yours is a standard merc +0.015" +0.030" bores for the standard pistons. I found somewhere that would do a +0.045" for Mercs, at not much more than the standard oversise price.

If your man can't get his cutting device far enough in*, there is a place up here does have one that will reach. Did all three of mine for £200 odd, including skimming the back face to make sure it was all perpendicular. Will need to look the number out, so let me know if you want to go this route & are stuck.


Disconnecting the autolube: Remove the pump, plug the oil inlet holes, then divide by 50 when you fill the tank! It'll smoke a bit more at idle, but that's about the down side of it unless you do a lot of pottering at low speeds.

* a vague attempt to prevent it all going bilge-ward

[mctaggart]

I am gonna pop down there this evening to have a look at the damage and also talk prices on what my best option is. He said hes got 2nd hand items also if i wanted to go down that route, i.e power head, standard pistons etc so I should have a wide range of price options.

I'll post up some pics later for you all to have a nose at!

[mctaggart]

It was quite obvious the rest of the engine was covered in a fine smearing of oil but this piston was dry as a bone, im not sure if oil has been starved to just this piston or if it has run lean on this piston i am not sure, but the top of the piston indicates it was running rich. Let me know what you think!


Notice how a corner of the piston has come away

Its a bit difficult to see but near one of the valves its scored quite deeply, i dont think a standard oversize piston will take enough of the scoring away. Is it possible to get an after market piston which will proivde more of an oversize bore?

[mctaggart]

Its got a fairly nasty score on the bore, at first i thought it was stuffed but i am now convinced a rebore should get rid of it after doing a bit of research. You can actually bore these out fairly big in relation to the standard size pistons.

Found out i can buy
Standard size pistons (Merc Original)
0.015 Oversize (Merc original)
0.030 Oversize (merc original)
0.040 Oversize Aftermarket piston
0.044 Oversize from Wiseco pistons

so i can bore out 1.1mm which i reckon is plenty!!

[davej]

I would certainly go pre mix, did this on mine quite some years ago as the older it became the more uncomfortable I became with the autolube system. What I have found is that the latest 2S oils don't smoke as much as they used to and don't seem to foul the plugs anymore.


Well done on sourcing all the rebuild parts and i lookforward to seeing how it progresses.

Dave

[9D280]

No pics! is the autolube one of these ones that injects into the air / fuel flow downstream of the carb, or does it bulk mix with the fuel beforehand?

I'm guessing what your pics show, but is the missing bit of piston on the exhaust side? Another Clamshell issue was the early ones had a precariously close to destruction spark advance - it didn't take much error to be sparking too soon, resulting in more fuel on the inlet side of the piston "dam" than the exhaust when it sparked. Net result when it went bang, because of the asymetry of the explosive mixture the piston was forced sideways into the exhaust port.... My engine stopped because the resulting shards shorted the plug! The "factory" cure was to retard the spark, which then was compensated for with a slightly lighter piston to allow it to spin faster & regain the lost gee gees.



I'll second DaveJ on the oils - much to my amazement I had a remarkably un-smokey engine after crawling up the Forth at canal boat speed for 2 hrs.....