Compression test ....

Steve C · Post by **Steve C** » Mon Sep 24, 2007 13:14

At 148,000 miles .. compressions read 220,220,220,215 ... there there .. have a nice drink of fresh Castrol RS 10w/60 to celebrate! Sorry, just a proud moment .. 3k more and it'll be my 100k mile Excel anniversary!

... and yeh, I'll ignore the bad earth since you failed to start withing 10 yards of home .. If anyone has an erratic temperature gauge, especially if it changes by a few degrees when the heated rear window is turned on (or the fans cut in, or any big current draw), immediately remove and clean the main engine earth under the carbs, even if it appears tight!

Help .. I think I'm going mad

Tanz · Post by **Tanz** » Mon Sep 24, 2007 13:23

What should the compression reading be idealy

Steve C · Post by **Steve C** » Mon Sep 24, 2007 15:10

I thought the spec was somewhere around 180-200 for the HC ... no manual to hand though.

I'm guessing my pistons have a fairly thick layer of carbon on them by now, reducing the area when at TDC and hence increasing the compression ratio - either that or my gauge is out a bit. The main thing is that they're all nice and even, and haven't changed for the last 70k miles at least!

Must admit, I'm pretty impressed with the engine having reached 148k with nothing other than routine servicing and mechanical sympathy when cold!

Lotus-e-Clan · Post by **Lotus-e-Clan** » Mon Sep 24, 2007 17:44

Steve C wrote: I'm guessing my pistons have a fairly thick layer of carbon on them by now, reducing the area when at TDC and hence increasing the compression ratio - either that or my gauge is out a bit.

Hope you're using the best quality high octane fuel.... or it'll be pinkerdy pink pink

Steve C · Post by **Steve C** » Mon Sep 24, 2007 20:58

It's set to 9 deg. at tickover and runs on decent fuel, normally v-power .. if I get stuck and have to use 95 octane it will pink a little if provoked, but I know when it will do it so drive around it!

Tanz · Post by **Tanz** » Mon Sep 24, 2007 22:13

Do you disconnect the coil to avoid damage to the ignition module when doing the compression test

I have got a gauge and was thinking of having ago. My engine has done 95k

Steve C · Post by **Steve C** » Tue Sep 25, 2007 10:18

I normally disconnect the fuel pump and let it tick over 'til the carbs empty - then disconnect the dizzy to ignition amp cable to stop the sparks. Remember to keep the throttle held wide open.

I've never disconnected the coil - in effect, with the signal side of the ignition amp disconnected, it's no worse than sitting with the ignition on and the engine not running so I don't see the need.

Lotus-e-Clan · Post by **Lotus-e-Clan** » Tue Sep 25, 2007 10:25

^^^^^ What Steve said plus I remove ALL spark plugs so that the starter can spin the engine at a decent rpm...

Redexcel · Post by **Redexcel** » Tue Sep 25, 2007 10:33

And the battery should be in good nick, or you'll get lower figures on the last cylinders as the engine speed drops.

And you should achieve maximum reading in 3 or 4 compression strokes of the cylinder if the engine is in good condition.

And....... I think that's enough for now.

Tanz · Post by **Tanz** » Tue Sep 25, 2007 13:17

I had a after market ingition system fitted so the amp is redundent.

I guess if i diconnect both sides of the coil i will be safe. I am a bit cautious because i buggered up the amp on a mark 2 astra some years ago.
Phil