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MG Midget and Sprite Technical - Cylinder honing

I fancy that the time is approaching to fit new piston rings to the 998. Cylinders 1 and 2 show 175 psi on compression test, 4 and 5 are 150 each. Importantly, 3 and 4 come up to 175 after squirting engine oil into them. The idle is pretty lumpy now, when it was always rock steady. I have a set of rings, and have dug out a cylinder hone that I acquired years ago but never used. I see that the stones are 180 grit. This seems a bit coarse to me. Will they take too much out of an already worn cylinder? Will the finish be too rough?

Also if I find there is a wear ridge at the cylinder top, what's the best way to remove it?
L B Rose

180 seems rough to me also ... but i dont have a clue to be honest

they make what is called a ridger reamer that removes that little lip.. i dont have any experiance with it.

prop
prop

I never knew the Spridget came with a 998 5-cylinder engine ;-)
David Smith

Its one of the donald healy special works engines.

haha
prop

For what its worth many years ago I used to work for Delapena Honing in Cheltenham who made (and still do) honing machines and equipment.

If what you have is a relatively cheap sprung loaded hone (as most DIY ones were) it will not give you a satisfactory result. It will of course "hone" the bore but it will follow what ever hole you have in your bores.

Much better would be to take it to a local engine shop and get them to either re-hone or if it is too bad a re-bore and hone.

If you search for Delapena Honing you will see what proper equipment is designed like rather than what is in effect a toy.
Martyn Wilks

Oops, silly typo! No I don't have a 5 cylinder engine. But my question is just about glaze busting to allow the rings to bed in. Instructions for fitting rings always say to remove glaze. However whenever I have had a block rebored I have always been surprised at how coarse the finish is.
L B Rose

The DIY one that I have, and used recently, made a good job of cleaning and prepping the cylinders for a new set of rings. They nicely removed some minor vertical csratches but I wouldn't expect them to true up a badly out of round cylinder. The hone is one sold by Sealey as a little kit for different sizes of cylinders, but it doesn't say what grit the stones themselves are.

A big difference in the drop between wet and dry readings on different cylinders would suggest to me some ring or cylinder damage beyond normal wear from a higher mileage engine. All the pistons have done the same number of strokes which may have caused some wear, but it would be much the same for each wouldn't it? If wear is greater on 2 of them it suggests something more is - or has - effected those two. A partial seizure perhaps if the back of the block hasn't been cooled adequately?

NB, you probably know this but only add a small amount of oil for the "wet" test as the volume added will alter the compression ratio as well as help seal the rings. So you also need to add exactly the same amount to each cylinder, and only before measuring each cylinder in turn, or you can get misleading results.

Addendum: The coarseness of the bore finish (cross hatching) is to help retain a film of oil on the surface, below the top level of the top compression ring stroke. This provides lubrication to the rings and additional seal if you have more than a single compression ring. The bottom "oil scraper" ring limits any excess oil, but doesn't remove it all
GuyW

I'm with Martyn
If you are going to hone it do it properly with a good rigid adjustable hone - If you havn't got one take it to someone that has - Flexible hones should be banned

If there is a ridge at all it should be removed first with a ridge remover, unless it is very minor, in which case the rigid set hone will straighten it out during honing

180 grit is fairly course, 280 would be more like it
and then if it's a racer or you're using molly insert rings, a light finish hone with 360 or even 400
180 is used for the first part of the honing process after a rebore to get to near size quickly

willy


William Revit

This thread was discussed between 20/04/2016 and 21/04/2016

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