Yamaha 85hp piston slap

[NinoEsteves]

Advice needed please! I had my two Yamaha 85hp motors redone by a mechanic. 1st it was in just for a service but was told that they would have to do bearings and change block, power head etc. got the boat back and took it for a test drive, on start up i found very loud noice coming from the motors wich was not there before. When i asked the mechanic what the problem was with the noice their reply was that it is piston slap and now they would have to reboar the block. On the invoice they did not use new rings etc instead replaced the part with used parts and only charged me a fraction difrence of new parts (rings and bearings). Could this piston slap be from using the wrong size parts etc and what will be the outcome if not corrected?

[99yam40]

can you say junk motor?

Surly this was not a yamaha shop that did this

[greasyshaft]

Slap the mechanic

[rodbolt17]

if work is south Africa is anything like some I saw in Venezuela.
***.

[NinoEsteves]

wits end

the charge for the repairs is almost the resale value! when the mechanic 1st phoned me to say their would be aditional work required i had a meeting with them and i wanted to replace the motors. as the nature of our business is to take tourists out on ocean safaris and we launch through the surf, i was very concerned about the reliability of the motors. the mac gauranteed that after the job was done the motors would be sound. please dont get me wrong not dissing any qaulified mac's as only after did i find out the mac actualy had no qaulification and is not surtified by Yamaha. what is piston slap and what causes it?

[NinoEsteves]

charge

sorry the charge for repaire is for work done, change bearings, rings, power head, conrod, block. thereafter work completed there was piston slap. i'm told that piston slap would we a very expensive repair.

[99yam40]

who knows what they did wrong or what they call piston slap.

Loose tolerances between pistons and bores, bearing to wrist pins and pistons, crank to rods bearings, crank main bearings to block, can cause knocks
Pr-ignition maybe where it fires to early and causes piston skirt to slap after if crosses TDC or probably lots of things I can not think about at this time
If there is a knock then you are better off getting a new power head. not used parts put into your power head.

They guaranteed the fix and it did not make it. See what they will do for you, but you are probably out of luck for them to cover their work

[NinoEsteves]

out of luck

There was nothing wrong with my block before! They phone me to say that they have put everything together and engine now blowing on bottom of block and that they have to pur in a nother used block.

[TownsendsFJR1300]

There was nothing wrong with my block before! They phone me to say that they have put everything together and engine now blowing on bottom of block and that they have to pur in a nother used block.

"Piston slap" doesn't develop when pulling an engine apart. The engine cylinder bore wears, the piston skirt wears. In general, over time, it gets louder over time/wear as the clearances increase and the piston eventual breaks.

IME, piston slap is kinda rare nowadays with the technology/auto lube, etc. On a pre-mix oiled engine, if the oil was NOT MIXED, that would help destroy and cause early wear. Rodbolt would be much more familar with the # of failures..

I actually had piston slap in my first 125cc,2 stroke, 1970 Yamaha motorcycle and rode it until the skirt literally broke off. Punched the cylinder out to the next size, new piston/rings, off riding again. That engine had a separate cylinder which could be re-bored, it was NOT part of the block..

Piston slap is a fairly light tapping, NOT a loud knocking. Sounds more like a bearing spun and knocking..

Re-using piston rings is pretty much a No No, at least a hone job and new rings if the cylinders withn spec's.

If there's another QUALIFIED mechainic available I'd be knocking on some doors. If stuck with this guy, I would insist on seeing what he's measuring, show me the worn cylinder bores, etc.


Good luck..

[grouper sandwich]

"
Piston slap is a fairly light tapping, NOT a loud knocking. Sounds more like a bearing spun and knocking..

What would cause a loud knocking?

[TownsendsFJR1300]

Something NOT put back together correctly or as you quoted me, a spun connecting rod bearing smacking / hammering the crankshaft.

If it was put back together correctly, it should be quiet as normal..


"engine now blowing on bottom of block and that they have to pur in another used block".
Confirms someone is "winging it" in the dark. A Major screw up IMO..



Is this a 2 or 4 stroke engine, model # and year, just curious..