12 replies to this topic

[fuzzypumper]

Hi

Ive just pulled down the 253 motor in the SLR.
To my surprise after measuring all the journals, bores and sighting the bearing part numbers, Ive discovered this motor is still
at factory spec, i.e. never been bored , no oversized pistons or bearings.
However I also measured the compresion rings end gaps as well but they seemed a little big to me.
I got measurements of between .041" to .060".

What should they be normally?

Cheers, Arthur

[FastEHHolden]

4 thou per inch of bore...so 14.5 thou

[TerrA LX]

I am assuming you removed the "old" rings from the pistons and put them down the bore to measure?

1. what condition is the bore?

2. how far down did you take the measure?

[fuzzypumper]

I am assuming you removed the "old" rings from the pistons and put them down the bore to measure?

1. what condition is the bore?

2. how far down did you take the measure?

The bore measures 3.626"
Yes I removed the rings and placed them in the bore.
At TDC the ring gap was .058" and at about 1.4" down the bore the ring gap was .045"

If you go by 4 thou per inch or bore rule then these rings have too much gap.

Also when I removed the pistoms I found the primary and secodaring ring gap positions
to be all over the place and not at 180deg apart.
Should I assume they normally move away from the position they where originally inserted?

Edited by fuzzypumper, 26 April 2011 - 11:05 PM.

[TerrA LX]

I am assuming you removed the "old" rings from the pistons and put them down the bore to measure?

1. what condition is the bore?

2. how far down did you take the measure?

The bore measures 3.626"
But is it round, not worn???

Yes I removed the rings and placed them in the bore.

At TDC the ring gap was .058" and at about 1.4" down the bore the ring gap was .045"
No point measuring at the top, too much bore wear here, insert the ring square into the bore 2" down.

If you go by 4 thou per inch or bore rule then these rings have too much gap.
Top ring 0.011 to 0.021 and Second ring 0.010 to 0.020 approx OEM spec.

Also when I removed the pistoms I found the primary and secodaring ring gap positions
to be all over the place and not at 180deg apart.
They do move around abit especially with high RPM and pinging.

Should I assume they normally move away from the position they where originally inserted?
Ideally they are not suppose to but so long as all the gaps are not aligned there should be no problems in general service.

[TerrA LX]

double post

Edited by TerrA LX, 26 April 2011 - 11:18 PM.

[Punchy]

fuzzy id suggest you remeasure everthing again your numbers dont add up

to start


Engine:
Capacity:
Cylinders:
Bore Size:
Stroke: 253 OHV 16v
253ci

253 V8
bore 92.07mm/3.625in
stroke 77.79mm/3.063in



You said your bore size is 1 thou over, (3.626) but if we push the ring down the bored a inch and a half you have 13 thou less ring gap.

That straight away says Tapered bore, which is to be expected from use, but your numbers suggest your ring placement wasnt "square" in the bore, or you have bigger issues at play.

If your on a budget, I know I am) Have the block checked, line honed to sqaure it up. reuse your old pistons with a new set of rings and have the machine shop give the block a good wash/clean and fit a set of 1 thou under cam bearing and have them fit the cam to it. Linish crank and reassemble.

Turn engine to 9000 rpm for maximum enjoyment

Edited by Punchy, 26 April 2011 - 11:26 PM.

[TerrA LX]

Yeah unless ur racing it have the block hot tanked and power hone and measure again, probably get away with rings only, have done myself a few times.

[rodomo]

Parallel stone hone, not a dunny brush, to true up the bore (within reason) then a quick wizz with the dunny brush to finish.
Cast iron (budget) rings. Super duper (hard) rings wont bed in to a bore of those tolerences.

You obviously have a worn bore but with new rings, the gap will come down.

If you choose not to bore it, I suggest leaving any ridge there (to avoid piston slap) but also to file a bevel into the top ring so it can't hit the ridge.

Disclaimer: This is all dodgy car yard rebuild methods, should see out the 20,000 klms warranty though

[TerrA LX]

^ Hey watch it buddy, I NEVER worked in a car yard, well there was that one day...

Alternatively fit oversized flat tops and a mild cam, they love it.

[fuzzypumper]

I'm not putting to much money into this one.
I re-measured the gaps again.
As I only have a vernier, I can only truly measure the tops of the bores which where 3.625", original size.
This fact coincides with the original numbered & sized bearings and original crank journals specs,
suggesting motor hasnt had a reco in the past.

I took ring gap measurements at the TOP(3.625"), at TDC(where most of the wear is), at 1.5" down the bore and at BDC.

Cyl...............1........2........3........4........5........6........7........8
TOP.............0.045 0.051 0.048 0.057 0.047 0.061 0.081 0.059
TDC.............0.061 0.063 0.064 0.070 0.067 0.076 0.100 0.074
1.5"Down........0.045 0.043 0.049 0.057 0.047 0.063 0.080 0.059
BDC.............0.047 0.053 0.043 0.059 0.047 0.064 0.081 0.060

As you can see at the TOP, most of the sizes vary between .047" to .061", with the exception of Cyl 7 which you could
park a Cadillac into. Either these rings are worn or this was the sort of quality, slap it together job GMH did back then.

At TDC where the wear is, the gaps generally increase between .013 to .021".

At 1.5" down the bore and at BDC, most of bores are the same and reflect the TOP measurement which is good I suppose.

Now, while I cant truly measure if the bores are round and true, the gap "differences" down the bore do give an idea
of how worn the engine is.
The lip at the top isnt too pround. In fact if you run your finger nail along it, you go right past it half the
time without catching.

Attached Files

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Edited by fuzzypumper, 27 April 2011 - 04:54 PM.

[TerrA LX]

I have an ACL gasket kit for sale if interested.

[fuzzypumper]

Thanks for the offer but already have an ACL kit.