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Posted By : David Christmas, 15-May-2006,
05:15pm
Could anyone please advise on the accepted compression readings for a Mk2 Vitesse. I have cold readings of 108 accross all six, and it is supposed to be a
rebuilt engine that has never run yet. Shining a torch through the plug hole shows a new or very, very clean piston, it spins over without the plugs in OK
and the oil light goes out within a couple of spins. The oil is also clean but motor has been standing for a couple of years in a restored rolling chassis.
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Posted By : John Davies, 15-May-2006,
07:00pm
David,
The absolute reading doesn't matter - compression gauges are not precision instruments, are uncalibrated and individual techniques differ.
What is critical is that the reading is the same across the block - which yours are, though ideally the engine should be warmed up.
Don't worry! Start it!
You're doing the right thing by spinning the engine with the plugs out to get oil circulating.
Pop them in and give it a whirl.
If this engine is brand new/rebuilt, you do need to consider the bedding-in of the piston rings.
DON'T use synthetic oil!
Use the cheapest you can find - I buy some B&Q oil, that is probably recycled.
On starting, let it warm up and take it for a run.
Then, drive with your foot hard down, then off, alternately. Accelerate and coast.
About four times a long coasting as acclerating. No need to rev it high, keep within 30-50mph.
This will increase the pressure in the cylinders to force the rings against the bores, then on the overrun the reduced presure in the cylinders will
suck up oil from the crankcase and lubricate the bores again.
Twenty minutes of this will bed-in the piston rings.
Then drive the car cautiously for another 500 miles (not all that day!)
Keep to less than 4K revs, but vary the speed all the time.
Dump the cheap oil, fill with the best.
And off you go!
Hope that helps!
John
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Posted By : Steve Cureton, 15-May-2006,
07:00pm
The fact that all compressions are nicely even suggests a good engine but the readings are lower than expected, squirt some oil in the bores and try
again, I suspect you'll fid the compressions are much improved. It's also imprtant to achieve a good cranking speed so remove the plugs in the other
cylinders while you're testing.
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Posted By : Nigel Gibbins,
16-May-2006, 08:02am
If the engine has never run the it's likely the ring haven't bedded in yet and so that would account for the low (ish) readings... this is
completely normal.
If they are all at 108 (all six) then I suspect this is a good engine and the compression will improve once it's run in properly (as John suggests)
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Posted By : Stephen Weblin,
16-May-2006, 09:09am
I would just like to renforce the point about running in the engine. When I had my Vitesse engine rebuilt, the process took some time and at
least initially the oil consumption before the rings sealed was considerable and noticeable. Blue smoke in the exhaust I thought that is why I
got the engine rebuilt in the first place!
Stick with it and use cheap oil with no additives - John says.
I remember somebody telling me that there was a time when Caterpillar put talc in their engines to help the bores and rings bed in. Not
recommended for Triumphs!
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Posted By : David Christmas,
16-May-2006, 02:50pm
Thanks to John, Steve, Nigel and Stephen for your postings , I feel much better for that information. It is a great relief and I will drain
out the existing oil and fill it with some cheap stuff to get the rings bedded in.
Many thanks
Dave Christmas