Piston slap

[Chris Edgar]

Been having problems regarding an excessively noisy 1275 engine in my wife's convertible...oils pressure & compression was good though. As was pulling power.
Symptoms were what I can only describe as a "gnashing" noise on idling & light acceleration. & it was gradually getting louder over time.

The noise didn't, to me, seem typical of anything & I had previously posted queries on it. Suggestions were to check tappets, pinking, big end bearings etc.
I had adjusted timing, set tappets & finally fitted new b/e bearings. All to no avail.

Took the plunge & pulled engine out to go to a local firm who would re-grind the crankshaft prior to new bearings being fitted.
The plan was for me to remove the crankshaft first...try getting the crankshaft pulley nut off an automatic car, where you can't lock the engine by putting it in gear! Was eventually done with an electric impact wrench.
Anyway, I digress.

Lo & behold, on inspection, the crankshaft mains & big end journals were fine, but the pistons were hitting the sides of the bores & the pistons were quite abraded. Hence the unusual noise.
The man at the engineering shop reckoned that at some time the engine may have been badly overheated. Maybe.
I've not heard of piston slap on these engines before...has anyone else?

So, the bores were honed & I fitted new (4 ring) pistons.
I also put duplex timing gear on and new b'e end bearings. Again.

Result: engine is like silk. Just murmurs along.
Deep joy!

[chrisryder]

i got a spare engine with my minor when i bought it. i finally took that engine apart in the summer and found that, similar to what you found' one piston had scoring on one side, so the piston must have been rubbing in the bore. this had gone to such an extent as to burr some of the ring grooves and grip onto a ring or two

after a bit of investigation we found the water jacket around the back of the block was very much full of rusty silt. so my guess is that it wasn't cooling enough at the back and the back cylinder was overheating.

when you had your engine out, did you look in the water jacket? take out any core plugs to see if it was blocked up? with the engine in, it's possible to take out the water plug on the right hand side, right at the back (sometimes it's a plug, sometimes a drain tap). If you take the plug out, does water come out? it should! it is possible to 'disempact' it by pushing (or hammering...) a screw driver down that hole to clear the blockage.

i hope your water jacket isn't blocked like mine was, or you could find your piston slap returning in due course!

[bmcecosse]

Best to undo the crank bolt while the engine is still in the car - socket on bolt head and T bar resting on the nearside chassis leg - and jab the starter..... You can always lock the engine with largish screwdriver blade on the starter ring gear....And yes if the rings have lost their temper due to running hot - the pistons can slap about. Sure the noise reduction isn't due to the nice new duplex timing gear ????????????

[Chris Edgar]

No, I didn't specifically look at the water jacket. Having said that, the waterways in the block, head & attached hose connections are very clean.
Also, draining & refilling twice has resulted in a far more effective heater in an engine which has always seemed to me to run cool, about 70 deg C..Anyway, I do hope that the problem does not return!
Knowing a bit about the previous history ( car abroad for 6 years), I would not be surprised if it had been allowed to overheat. Better say no more!
All 4 pistons were scored BTW, on both sides, although more on the "pressure" side, I'll post some photos in a day or two.

Thanks for the tip on using the starter to free the bolt!
The reduction in nasty noise definitely not due to the timing gear, although the new timing gear is quieter than the old.
I found, on initial start up, there was noise from the new gear. Took the cover off & found that the chain was JUST catching on a part of the cover which had a pressed in area to accommodate a strange device attached to the outside of the cover. It is a sort of square tube which seems to have no function.
I was able to beat out the depression & the "job's a gud 'un"

I am very impressed with the quality of the duplex timing gear for the price.

I was also very impressed with Lancaster Engines, who:
Took the pulley bolt off...
Inspected & measured the crankshaft ( & didn't say "Ooh this'll need re-grinding!)...
Inspected, measured & honed the bores...
Fitted the con rods to the new pistons & gudgeon pins...
Lent me a ring compressor for the weekend...
& charged only £20!

thanks for the replies

regards
Chris

[bmcecosse]

That does sound like good value!

[sirrom]

I recently stripped and rebuilt a 1098 engine and prior to a rebuild the water in radiator was clean but when taking the head off the rear water jackets were totally clogged up, even pushing screw driver down wouldnt clear it. In the end when I had a bare block I ended up using a water blaster down the jackets and back through the rear side block drain tap and was amazed what came out. It left quite a resdue over my driveway. There was a build up behind the side frost plugs as well.
Was pleased I made the effort after many years of build up in the system

[rayofleamington]

I've not heard of piston slap on these engines before...has anyone else?

I've certainly had it on a 1098 - although that one had very worn bores so no big surprise!

£20 for all that is excellent - normally it's £20 just to hone an already stripped & cleaned block

[Chris Edgar]

You must be familiar with the distinctive noise it makes, Ray.
It's something I think I would know if I heard it again!

regards.
Chris