Bore or replace cylinder liners

[Jens Munk]

Hello,

What is the maximum acceptable cylinder wear? I have the heads of for another reason and will have the cylinders checked now that I am in there and because I know it is a relatively high mileage engine.

If it is due for an overhaul, what would you recommend? Should I get it re-bored and new pistons fitted or will I be better off with a 3.9 liter upgrade? 10.5:1 3.5 liter pistons are very expensive. In fact you can get a 3.9 liter upgrade kit including pistons, liners and bearing for ½ the price.

Thanks,

Jens.

[enigmas]

You've just answered your own question.

[djm16]

What is the maximum acceptable cylinder wear

Wear is unacceptable when
1) good compression and
2) low oil consumption

cannot be produced by replacing the rings (sometimes with oversized rings filed down).

There is not an exact figure.
Rover pistons in the 3 litre at least come with an original clearance of a few thou. Yet a new BMC B series motor had 20 thou or more clearance at the top of the piston.

[enigmas]

Don't file any oversized rings down even if such things existed. Increasing the gap on the next size up ring will result in an 'oval' ring in a round cyl. The engine will produce lots of blow-by. If you know an old time engine-reconditioner who knows his stuff you can have the thrust side of the skirts knurled. Lightly hone the bore (it's quite cheap to have a professional shop do this for you and also remove any ridge that may be at the top of the cyl.

You need to check the top ring land for wear. There should be no more than .004" side play on the top ring land. The other lands will show very little wear as they are protected by the top ring. If there is wear some machine shops (with history) will machine the top land to the next size up ring. I have done this with a set of pistons that were hard to obtain new. Piston manufacturers (JP Pistons) will make a set of rings or even just one for about $14 AUD. so you can have a top ring made and fit the remainder as standard size. I'd limit bore clearance to about .004". Just tell everyone you running racing clearances.

To check, invert the piston in the cylinder and fit a feeler gauge between the bore and the thrust side of the piston (at the bottom of the skirt) and cyl. Fit the same pistons to the same cyls.

Never measure piston clearance at the top of the piston (pistons are also cam ground/eccentric)Pistons are made narrower at the top to allow for thermal expansion. The alloy at this point is also the most dense (thick)always invert them and measure on the thrust sides.

There is a place in OZ that does thermal barrier/slippery coatings for pistons. There's one process for the top and something else for the skirts. One skirt process in particular will add .003 to the skirt thickness. This is space age technology not a tin coating or such like.

As an aside, I built up a twin cam MGA motor in my youth like this and although it had to be warmed up to expand the pistons, it went like stink. At a later date I rebuilt the engine with new specially made pistons...the engine was never any faster.

[djm16]

remove any ridge

If you are still on the original rings, then replacement rings usually come with a "ridge dodger" top ring. It has a slight chamfer on the leading edge. That way you avoid taking out the blocker to a machine shop.

[Jens Munk]

I guess it doesn't fall in these categories. The compression is so good that I have problems with pinging and the oil consumption is acceptable after I got the intake manifold gasket replaced. This gasket had a serious leak.

During the winter stand-still I had the valves machined and ground, replaced the cam, cam bearings, lifters, oil pump, timing gear and chain as well as any gasket involved. Unfortunately I didn't listen to you and installed original style ultra thin aluminium head gaskets with the result it pings under load more than it did before. Lesson learned, so now I am installing modern and thicker head gaskets to reduce the compression a bit and hopefully reduce the pinging.

I checked the cylinders with a cylinder gauge and they are about 0.08 mm = 0.003" over at max at the top and less down to spot on toward the bottom.

The reason I am concerned about wear is not really performance or oil consumption but imperfections in the sound. I am probably a perfectionist in this respect and way too picky. However, here is what I hear:

When it is cold, there is some mechanical noise at any rev and more under load.

When it has warmed up, idle is good and reving it up is also good. No mechanical noise and valves are obviously completely silent with new lifters and gear/chain. Driving at constant speed is also good, but under acceleration and hill climbing and before the onset of any pinging, the engine gets more mechanically noisy.

Am I too picky? If not, are we looking at a complete rebuild? Do you suspect cylinder/piston wear, main bearings, connection rod bearings, else?

Thanks,

May 26, 2014 12:33:45 GMT djm16 said:

Wear is unacceptable when
1) good compression and
2) low oil consumption

cannot be produced by replacing the rings (sometimes with oversized rings filed down).

There is not an exact figure.
Rover pistons in the 3 litre at least come with an original clearance of a few thou. Yet a new BMC B series motor had 20 thou or more clearance at the top of the piston.

[enigmas]

There are several things you can do. Most of your issues appear due to detonation (high compression, low octane fuel and an ignition curve that is probably too fast for the fuel you use)

Consider going green! Your engine is ideal for an LPG conversion and will run like a sewing machine on this alternative fuel.

If you must stay with petrol?(what percentage of ethanol is in the fuel you use?) Ethanol will cause all sorts of unseemly reactions with the fuel system as well as other issues with corrosion and water entrainment.

When the heads were off there was an opportunity to do some relief work to the combustion chambers. There's a pip in there that can be removed and some material around the valve heads to de-shroud them a bit. You could have also removed a bit of material from the top face of the piston around the periphery. In tandem these small mods would improve both flow and drop the compression down.

You may need to slow the advance weights down in the distributor and perhaps disconnect the vacuum advance, as your car is probably experiencing some pinging on light throttle loads at higher engine speeds when both the centrifugal advance is all in and the engine is pulling high vacuum... meaning the advance capsule is also adding to the total mechanical advance.

Some P5B distributors are only fitted with one spring...if so fit a secondary. You can also grind the weights down to reduce their inertia. (A lighter weight needs to spin faster for the same movement. If you do this remove weight at the opposite end to where the weight pivots...just do this progressively a little at a time and note the changes...although you may not have the patience for this repeated task.

[Jens Munk]

Thanks.

LPG is not an option here (Denmark) as it is essentially not available. The highest generally available octane rating here is 95 and the Rover V8 required 100. The closest I can get is Shell, who has octane 98. In addition I use Castrol Valvemaster Octane booster and lead substitute. By law there is 5% ethanol in the petrol here.

To check the too advanced ignition, I could as you say, try to disconnect the vacuum advance or perhaps just adjust the timing a few degrees and see if it has any effect. It only takes a trip to the nearest hill to test, so it is not a major deal.

May 27, 2014 12:19:20 GMT enigmas said:

There are several things you can do. Most of your issues appear due to detonation (high compression, low octane fuel and an ignition curve that is probably too fast for the fuel you use)

Consider going green! Your engine is ideal for an LPG conversion and will run like a sewing machine on this alternative fuel.

If you must stay with petrol?(what percentage of ethanol is in the fuel you use?) Ethanol will cause all sorts of unseemly reactions with the fuel system as well as other issues with corrosion and water entrainment.

When the heads were off there was an opportunity to do some relief work to the combustion chambers. There's a pip in there that can be removed and some material around the valve heads to de-shroud them a bit. You could have also removed a bit of material from the top face of the piston around the periphery. In tandem these small mods would improve both flow and drop the compression down.

You may need to slow the advance weights down in the distributor and perhaps disconnect the vacuum advance, as your car is probably experiencing some pinging on light throttle loads at higher engine speeds when both the centrifugal advance is all in and the engine is pulling high vacuum... meaning the advance capsule is also adding to the total mechanical advance.

Some P5B distributors are only fitted with one spring...if so fit a secondary. You can also grind the weights down to reduce their inertia. (A lighter weight needs to spin faster for the same movement. If you do this remove weight at the opposite end to where the weight pivots...just do this progressively a little at a time and note the changes...although you may not have the patience for this repeated task.

[Jens Munk]

Although it does not appear to be the trouble according to the other posts, then out of curiosity, how complicated is it to replace the liners in a Rover V8 engine?

May 26, 2014 10:47:56 GMT enigmas said:

You've just answered your own question.

[djm16]

Are you way too picky?
Yes!

A noisy engine that gets quieter as it warms might well have a very small exhaust manifold leak. If you have a stethoscope it is very easy to find the leak.

[enigmas]

Jensmonk1, when I made reference to the ignition timing I didn't mean just backing off the distributor a few degrees...I meant slowing down and reducing the amount of advance both centrifugal and vacuum.

As for fitting new or larger dry liners to your existing block, be prepared to spend a bucketful of money and then hope they don't shift or come loose. It would be better value as suggested earlier to get hold of a good second hand 3.9 engine.

[Jens Munk]

I know that it's not adequate to just back it off as a permanent solution. It's just to test the effect of it and then start messing with the advance mechanisms.

As for the liners, what you say is kind of what I expected/feared. It seems too easy to just pay Rimmer a few hundred pounds for a set of new pistons, liners and bearings and then be almost ready to go.

Anyway, it is about ready to be fired up again with new thicker head gaskets that hopefully help on the pinging. I will also go through the exhaust and check for any leaks as suggested.

May 28, 2014 14:01:35 GMT enigmas said:

Jensmonk1, when I made reference to the ignition timing I didn't mean just backing off the distributor a few degrees...I meant slowing down and reducing the amount of advance both centrifugal and vacuum.

As for fitting new or larger dry liners to your existing block, be prepared to spend a bucketful of money and then hope they don't shift or come loose. It would be better value as suggested earlier to get hold of a good second hand 3.9 engine.

[Jens Munk]

Enigmas,

You are absolutely right. All issues were apparently due to detonation. I completed the installation of 1 mm modern head gaskets today and not only is sharp and clear pinging at high loads gone but also the "roughness" at more moderate loads. In fact it runs like a sewing machine now, and I am very happy. I was really getting nervous that I was facing some major engine work.

On to the next project - new front and rear window seal.

May 27, 2014 12:19:20 GMT enigmas said:

There are several things you can do. Most of your issues appear due to detonation (high compression, low octane fuel and an ignition curve that is probably too fast for the fuel you use)

[enigmas]

Well congratulations..I'm pleased that you managed to sort your issues without great or unneeded expense. Nil desperandum.