Engine Damage

[RobinGi]

Did some work on the carby the other day where I straightened up the throttle cable
Next day went for a drive and about 2k's up the road a loud knocking stated in the engine
got towed home and pulled off the head and found this in cylinder 4



Cylinder 1 had this in it


and cylinder 3 had some metal in it a well


the head it pitted, it was a reconditioned head that I put in less than 200km ago



any theories on this ?, I would have suspected that if I dropped something into the carb it would have gone into one chamber not three!
all the spark plugs loo fine, SP4 had closed up and the bores all feel fine


next thought is I don't have a lot of coin to throw at this, any ballpark figure on a rebuild for this in melb?
I the corner of my garage I have a 186 condition unknown, it can be turned by hand should i just throw it in and hope for the best ?

Any Advice apprecieated
Rob.

[Harv]

Any idea what is was that you dropped (eg are there any missing bits on the carb, did you pull anything else off when the carb was open)? If you dropped more than one item, they may sit in the inlet manifold and get sucked into different cylinders.

Is that the cut-off tail of a splitpin in Cylinder #4?

Spinning engines can do some funky things when metal gets fed to them. I once had a Mini motor drop a gudgeon pin clip. It went up the piston, danced around in the combustion chamber, then back down the piston at another location. The cylinder, head and piston looked like a slaughterhouse.

Cheers,
Harv

[RobinGi]

Thanks Harv,

no all parts were accounted for on reassembly.
the embedded item in #4 is too thick to be a split pin associated with the carb, its 3.5 x 15mm the bit in #1 is about 5mm
only took the carb off to fix a leak from the Jet inspection screw, noticed it while fixing the throttle cable.

Rob.

[Harv]

There is not much in the carb itself that can go AWOL. Check for missing throttle plate screws. They should be brass though. Throttle plate and float bowl vent can both come loose, but are too big to pass through. Is the nut still on the air cleaner clamp?

Cheers,
Harv

[ardiesse]

Rob(1),

You asked how much it'll cost to fix -

It looks worse than it is.

First: check the cylinder head. The valves don't look damaged. Get the #4 spark plug and screw it into the hole. Put the head upside down on the bench and pour petrol into the combustion chamber. Shine a light into the ports after a minute or so. If you can see petrol weeping into the ports, you'll need to grind the valves. Otherwise the head's fine.

Second: piston. The crown's good and mooshed up, I'll grant you. But there's probably no other damage. If you're keen, drop the sump and pop number 4 piston and conrod out. Inspect the piston for broken ring lands. If you can spin the top compression ring in its groove, then the piston's fine.

Third: big-end bearing. It probably won't have sustained any damage. But since you've pulled the piston and conrod out, assemble the big-end cap (with bearings) back onto the conrod and torque to specs. Measure the internal diameter of the bearings, and the OD of the crankpin. Compare the two. If the oil clearance is out of spec, replace the bearings.

My guess is that you can restore the engine to service for the price of a top-end gasket kit.

Rob(2)

[Harv]

With the piston crown so chewed up, would the sharp bits get hot (like heavy coke) and cause early pinging? Gently round off with a die grinder?

[RobinGi]

Cant think of anything that I could have dropped into the manifold that would have been of that dimension, the nut in the cleaner is welded into place and still there.

Called a mob in Dandenong and was quoted around $2800 changeover (Long)

The motor's a 202 in FB ute besides the piston the rest of the engine looks very clean, checked the spare 186 and it has gunk built up over everything so not to keen to put it into service.

thinking the same as Rob(2) pop out piston #4 and found everything looks to be in speck but the object has hit in some spots around the edge of the piston and mushroomed out



So thinking replace pistons/rings/bearings
But require info on how to tell if the piston and bearings are of standard size or OD from memory there's is usually a number stamped on top of piston to indicate a larger size ? On the piston next to the gudgeon pin is an "F" but cant see any other markings
on the bearing is - 001 - HOLDEN - FR5 RM500 any idea what this is indicating?

[ardiesse]

Rob(1),

You're one step ahead of me. My blunt advice - don't replace the pistons. A couple of strokes of a file will cure the mushrooming bits, and as Harv suggests, will also take the high spots off the piston crown. If you have a vernier caliper, set it to the diameter of the piston crown at an undamaged spot. File the shiny metal off the side of the piston crown until the vernier will just slide past. And since you've taken the top compression ring out, why don't you fit it into number 4 bore, slide it down 3/8" or so with the piston, and measure the ring gap? That will help you decide if you need a new set of rings. (Thinks: 0.016" ring gap for new bores and rings, 0.025" ring gap perfectly OK, 0.040" - 0.060" ring gap, think about new rings, >0.070" ring gap, replace rings.)

To determine the size of the piston, measure across the bottom of the piston skirts. 3.625" is standard 186/202 bore, so I'm expecting either 3.665" (+040) or 3.685" (+060).

Could you post a photo of the big-end bearing shell in the conrod? That'd be a great help.
But meanwhile, when you popped number 4 piston and conrod out, did the conrod-side big end bearing shell stay on the crankpin, or drop out of the conrod without any help? (If the answer is yes, then the bearing shell has been deformed, and is best replaced. High-mileage and/or thrashed red motors do this to big-end bearings).

At the rate you work, you can have the piston cleaned up and the motor reassembled and started by the weekend. Holden engines are really quite forgiving.

Rob(2)

[RobinGi]

Thanks for the replay Rob(2)

the piston measures @ 92mm = 3.622 standard, good to know

All the bearing shells stayed in place when I removed them

will check the ring gap tomorrow


offending part in background !

[ardiesse]

Rob(1),

The bearing shells don't look damaged, and there are no scores in them. I figure they're good enough to re-use.
Slightly surprised that the pistons are standard size . . . it must be a low-mileage motor.

Rob(2)

[RobinGi]

water test on the head looks good, no seepage past the valves
couldnt find my feeler guages to measure so i did a rough measurement with the vernier and got 2.3mm = 0.090
interesting as a recent compression test 135 130 127 145 130 135



the second ring measured @ 1mm


Thanks again Rob(2) for the info.

Rob(1)

[ardiesse]

Rob(1),

With ring gaps of that size, I'd suggest a hone and new rings, which will wake the motor up nicely. Bearing replacement optional.
I'd normally expect compressions around 180 psi for a high-compression red motor (that's what I remember from an X2 I had).
140 is what you'd get with a healthy grey motor.

What condition are the bores in? Look particularly at the front of number 1 cylinder for excess wear and a big lip.

Rob(2)

[RobinGi]

Wear on the bore is hard to measure so I would estimate the width of a A4 print paper which is 0.1mm and it looks like carbon build up contributing to the step.

[ardiesse]

That's a good sign. Scour the carbon buildup off with Scotchbrite at the top of the bore to get a better idea of the wear in the cylinder bore.
Greatest bore wear occurs on the right and left sides of the bores, except for number 1, which often wears out at the front of the bore.
And when re-ringing engines, the important thing is not oversize so much as out-of-round and taper. Generally you can tolerate up to 0.008" wear in the bores.

Rob

[ardiesse]

Oh, and - you can estimate the wear in the cylinder bore with a piston ring and feeler gauges.

Clean the carbon off the top of the bore. Insert a comparatively unworn ring completely, but squarely, just inside the top of the bore. Measure the ring gap. Push the ring squarely down into the bore so it sits just below the ring ridge. Measure the gap again. Subtract first measurement from second measurement, then divide by 3.

So let's say you measure 0.040" gap first and 0.063" gap next. 63 - 40 is 23, divided by 3 is 0.008" approx.

Rob