piston ring size problem

Seight-V8 · Post by **Seight-V8** » Mon Jan 09, 2017 8:54 pm

hello all,

well after solving a crankpin bearing problem, I thought that would be it and I could finally put something together....how wrong.

next problem.

I bought some grant piston rings from real steel 4.6v8 +0.020ins size.

But when I try them in my block with a 94.5mm bore (standard +0.5 rebore)

The rings are gapped, or there's no material to remove to gap them with.

This is my third engine rebuild and I've always gapped the rings......

Hmmm so I thought.

If I hold the piston ring together and create the gap with a 0.40mm feeler gauge, and measure the outer diameter with a Vernier.....I only get 94.00mm diameter.

So does this mean I have the wrong diameter piston rings?.....

Cant even find grant land rover 4.6 +0.5mm piston rings on the grant website.....

I've also worked out the circ length of the ring, and it also matches the standard 94.00mm bore size......

Again points to wrong size rings......

Real steel do sell +0.5mm rings, just wondering if I have the wrong ones.

cheers

scott

unstable load · Post by **unstable load** » Mon Jan 09, 2017 11:27 pm

Wow, it sounds like you have been sold all the suspect bits in the store.

minorv8 · Post by **minorv8** » Tue Jan 10, 2017 5:40 am

What is the actual end gap when the ring is fitted in the bore ?

DEVONMAN · Post by **DEVONMAN** » Tue Jan 10, 2017 8:29 am

minorv8 wrote:What is the actual end gap when the ring is fitted in the bore ?

It's not really accurate to measure the diameter of a piston ring by holding it with a feeler in the gap ??

Seight-V8 · Post by **Seight-V8** » Tue Jan 10, 2017 6:32 pm

what started it was the fact that when I've come to start gapping these piston rings, they don't need gapping some are already too close to the largest gap that the LR manual specifies.

I was only trying to work out the actual diameter of the rings quickly, not gap them this way....

The circ lengths seem to suggest 94.0mm bore rings not 94.5mm as those would be 1.56mm longer around the circ.

What would be the worse case if I did fit 94.0mm piston rings to a 94.5mm bore is my question......how good would the bore seal be, even if they where gapped correctly.

I'm just not sure now these rings are for a 94.5mm bore.

Real steel do sell both bore piston rings, and they do have different part numbers, so I would say they are different, in diameter & circ lengths.

And I cant tell from the box or the rings, what they actually are now....

Not sure I can trust the set I have, with the rings being so critical to the state of the engine....or am I over thinking this whole problem?

cheers

scott

DEVONMAN · Post by **DEVONMAN** » Tue Jan 10, 2017 7:30 pm

I bought rings from Real Steel some time ago and they were described as pre gapped. Maybe a quick call to them to establish if yours are pre gapped.

Seight-V8 · Post by **Seight-V8** » Tue Jan 10, 2017 7:49 pm

yes that's a good idea.....looked around and it doesn't really say if the are gap sized or not.

Some of the 1st compression rings are slightly over 0.5mm gap size but only just....maybe 0.55mm at worst.

cheers

scott

minorv8 · Post by **minorv8** » Thu Jan 12, 2017 6:25 am

How fresh is your overbore ? One thou extra in diameter equals 3 thou increase in circumference. That means that for a given ring the ring gap is also increased the same amount.

I am currently doing a budget rebuild to a 4.6 engine, new bearings and rings etc. Used block and used pistons. I noticed the same thing, even if the bores are not that worn the ring gap is also very close to the 0,50 mm and 0,65 mm ring gap values.

I would recommend new rod bolts if you don´t have them already. Factory manual that I have does not specifically say to replace them (see below). I tried to use old bolts but at least one started to let go. So, I fitted new ones.

3. Remove 2 bolts securing each connecting rod
bearing cap, remove caps and recover
connecting rod bearings.
CAUTION: Keep bearing caps, bearings and
bolts in their fitted order.

stevieturbo · Post by **stevieturbo** » Thu Jan 12, 2017 11:12 am

Are there no part numbers with the supplied parts ? What sort of packaging ?

I really dont think you can measure a piston ring in that manner....although dont honestly know how you would measure one.

But it isnt uncommon for people to use a slightly oversize ring in a bore and adjust the gap to suit, if for some reason the next ring size down created too large a gap.

The differences in bore diameters here really are small so I dont think it would be a huge issue.

And I would never take for granted any ring might be pre-gapped....always check.