Can a layperson with normal garage equipment determine if a rebore is required?

[jedwards]

Gentlemen,
My 1953 Series 1 2litre, has poor compression, and I believe, shot value guides and seals. I now have the head off but wanted to get this groups view on if an average home mechanic with normal measuring gear is able to determine if a costly rebore is essential or not. The bores in my engine seem to have no wear lip at the top of the cylinders and no obvious imperfections. In fact I was amazed at how good they seemed.
The bores should be 77.8mm diameters, so I can measure those with a vernier to see how far they have drifted.

Is there a technique for measuring piston ring gaps (in situ ) that could tell me if the rings themselves are badly worn?

I understand that I check the crank bearing clearances to see if they are in or out of spec.

Many thanks
Jeff

[bblaze]

you really need an inside micrometer and measure at 90 degree angles at top, middle and bottom of bore.
To measure ring gap
insert ring into bore and use a piston top too slide it down about inch from the top and measure gap with feeler gauge
cheers
blaze

[101RRS]

Series 1 engines do burn exhaust valves so that may be the reason for your low compression.

Garry

[roverrescue]

Is the block in the engine bay or on a stand
In my experience if you take a cleanish stripped block with crank and cam to a good engine machine shop

They will run a cubit measure ;) over the components and give an opinion on the way forward?

With theor Mk1 eyeballs a set of bore gauges and few micrometers a seasoned machinist would have the bits sized up in a few minutes ???


If you wanted to DIY
First thing is do you have cross hatchlings in the bore consistently top to bottom in all pots ?

Buy a telescoping bore gauge of correct size and to be honest the repeatability of an upper spec digital vernier will do to assess ovality.

S

[1950landy]

You may not be able to check with a Vernier for a couple of reasons because the top of the block is sloped the top of the bore will have a chamfer to help feed the rings in because it is difficult to use a ring compressor that is if it has never been re bored ( I have used a ring compressor but you need to be careful you don't brake a ring ) , also you need to measure from the top piston ring down measuring top & bottom of the bore. It could also be that the pistons being alloy are worn. These engines had a chrome bore & have a habit of glassing up . The other thing could be the rings could be gummed up & sticking in the ring groves. I would recommend getting a engine reconditioner to measure it , they will also need to measure the pistons.

[Blknight.aus]

Depends on what you consider normal garage equipment...

if you're garage looks like the back of my car on some call outs, yes.

But that said.

the first step is your MKI eyeballs, look at the hatching. where its worn away will be your largest gaps.

pull the rings off of a piston, insert it in its bore upside down and turn it slowly as you drop it in, if it doesnt stick thats the first part.

next insert a ring and push it part way down like you were going to do a ring gap check, insert the piston about an inch with the thrust side of the piston on the thrust side of the block
now using a bit of wire of known size (mig wire is a good choice as you can get it in lots of sizes) try to gently work it down the gap on the thrust side. if it wont fit, adjust it with a hammer until it does fit. and fits snugly.

now wrap an elastic band around the piston to keep it in place and then pull the ring out, insert the wire from the bottom and it should fit snugly in the same place. if its a lot looser then make a fatter bit of wire.

when you have a snug fit thats your minimum oversize on the current nominated piston size. measure the thrust side of the piston and if its different from the nominal diameter then its the thrust side and the wire size that then sets the nominal minimum oversize.

If the nominal minimum oversize of thrust side and wire size is smaller than the nominal piston size youve got problems.

[5380]

Gentlemen,
My 1953 Series 1 2litre, has poor compression, and I believe, shot value guides and seals. I now have the head off but wanted to get this groups view on if an average home mechanic with normal measuring gear is able to determine if a costly rebore is essential or not. The bores in my engine seem to have no wear lip at the top of the cylinders and no obvious imperfections. In fact I was amazed at how good they seemed.
The bores should be 77.8mm diameters, so I can measure those with a vernier to see how far they have drifted.

Is there a technique for measuring piston ring gaps (in situ ) that could tell me if the rings themselves are badly worn?

I understand that I check the crank bearing clearances to see if they are in or out of spec.

Many thanks
Jeff


Jeff,
If you clean up the top part of the cylinder bore and wind the piston down the bore, if the bore is worn, you will see a noticeable lip or step below the uppermost reach of the top piston ring. Above the reach of the top ring, there is vitually no wear, so the bigger the lip, the more wear. Any wear will be greater on the piston thrust face areas on the sides of the bore, not the front and back. If there is a step there, you have to get someone with an internal micrometer to measure the worn and unworn areas to determine the wear. My 80" had vitually no lip or measurable wear, and visible honing cross hatch, so I didn't have to rebore it. I was lucky enough to find a set of std pistons and just honed the bore and fitted the rings etc as described in the Land Rover #4291 work shop manual. Regards 5380