Ali King Posted October 11, 2020 Report Share Posted October 11, 2020 Hi All, I've just carried out my first (ever) compression test on my 4A and here are the results: Engine cold, closed throttle: 1) 160; 2) 160; 3) 160; 4) 145 Engine cold, open throttle: 1) 162; 2) 160; 3) 160; 4) 143 Engine cold, open throttle, a little oil down the plug hole: 1) 176; 2) 174; 3) 176; 4) 155 I suppose my slight concern is that cylinder 4 is about 10% different to the others - which are very consistent. Is this anything to worry about and how may it be explained? Just for info, I got my tester from a chinese company on ebay (although shipped from Manchester) - it cost £11.50 including postage and looks identical to one at Machinemart for £33.59! Obviously I don't know how accurate it is, but so far I'm impressed by the consistency in readings. Thanks for any help. Alistair. Quote Link to post Share on other sites
AndrewMAshton Posted October 11, 2020 Report Share Posted October 11, 2020 Hello Alistair, I checked mine, or had them checked for me by a chap who owns a garage so he used a top end piece of kit, I got 180,180,180,190, I have a 4A, 86mm pistons, standard head, it sounds like your rings are worn, much blue smoke on start up? Cheers, Andrew Quote Link to post Share on other sites
ctc77965o Posted October 12, 2020 Report Share Posted October 12, 2020 your data shows that when you add oil the difference between No4 and the others increases... it also shows all compressions are higher with a bit of oil in the bores. My conclusion: engine is a little worn, but nothing to worry about. No4 has a valve sealing issue.. if the car has stood for a while then also no issue as it likely cleans-up with use, if its in regular use this could be early warning of a burnt valve...suggest drive it & moitor every few 1000 miles with your new gauge. Quote Link to post Share on other sites
Waldi Posted October 12, 2020 Report Share Posted October 12, 2020 Hi Alistair, Have you checked valve clearances? Readings are not bad, to me the compression test is more a comparative analysis than an absolute (value) measurement. Regards, Waldi Quote Link to post Share on other sites
Ali King Posted October 12, 2020 Author Report Share Posted October 12, 2020 Thanks guys. Not much smoke on startup. So I think my plan of action is to check valve clearances in the not too distant future and recheck compression periodically. I'll report back if I find it's the clearances. Alistair. Quote Link to post Share on other sites
Andy Moltu Posted October 12, 2020 Report Share Posted October 12, 2020 The exact pressure is not that important (- affected by many things such as compression ratio and the calibration of the guage) It is important that the tappets have been checked before the comp test. Should really be done with the engine warm and with the trottles wide open. Crank over a about 6 times until the guage has peaked. Less than 10% between the cylinders is generally considered acceptable. If a drop of oil down the bores doesn't change things much it is possible you have a valve issue although a head gasket failure could do it there are usually other signs such as overheating or exhaust gassing in the coolant. Quote Link to post Share on other sites
Lebro Posted October 12, 2020 Report Share Posted October 12, 2020 (edited) I had 1 cylinder (No.3) a fair bit down on compression (TR3) oil did not make much difference, a leak test (compressed air into the spark plug hole with valves shut) revealed air leaking past the exhaust valve. This promted me to remove the head, & refurbish it while lockdown was here. There was no visible sign of any seat erosion, but had hard seats put in anyway, along with new valves & guides. Bob. leak tester (home made) Edited October 12, 2020 by Lebro Quote Link to post Share on other sites
Ian Vincent Posted October 12, 2020 Report Share Posted October 12, 2020 If you aren’t up to manufacturing your own leak down tester, you can buy kits on eBay for less than £20, and they do work. This assumes that you already have a compressor, (or access to one). Rgds Ian Quote Link to post Share on other sites
john.r.davies Posted October 12, 2020 Report Share Posted October 12, 2020 For consistency, the test should be done with the engine warmed up. And always with the throttle wide open. Your oil test shows a rise in pressure,which excludes a valve leak as the cause, which leaves ring leaks, but do it again warmed up to be sure. 'Accuracy' is not an issue, as compression gauges aren't precision instruments, doesn't matter if they are Snap-On or So-Cheep, they cannot be compared, unless you use one on two engines on The same day, same p!ace! So the absolute pressure is unknown. What they let you do is compare the bore pressures across the block, as you have done. Quote Link to post Share on other sites
Chris Hubball Posted October 12, 2020 Report Share Posted October 12, 2020 Hi Bob I am interested in your home made leak tester any chance of a brief description of how you made it, I tried to make one myself but could not find a way of sealing the tube to the old spark body. Cheers Chris Quote Link to post Share on other sites
Andy Moltu Posted October 13, 2020 Report Share Posted October 13, 2020 You've established there is a problem with no4 because you have a disparity of over 10% and this is only on No4. Possibilities - blown head gasket - usually accompanied by overheating and gassing in the coolant. Valve seats worn or burnt. Piston ring problem - usually excessive breathing or oil consumption accompanies this. What prompted the compression test? If the car was running OK and not guzzling oil or blowing smoke it's probably he valve seats. In pretty much all eventualities you are going to need to remove the cylinder head to check the valves are sealing. Upturn the head and fill with paraffin. If No 4 drains quicker than the other 3 dissasemble the head and check seats and for cracks. If the head checks out Ok then drop the the sump and remove No4 piston to check the rings & bores. Whilst the head is off check the cylinder liners haven't dropped. Quote Link to post Share on other sites
john.r.davies Posted October 13, 2020 Report Share Posted October 13, 2020 (edited) The oil test excludes a valve seat problem, as I already pointed out. Edited October 13, 2020 by john.r.davies Quote Link to post Share on other sites
Andy Moltu Posted October 13, 2020 Report Share Posted October 13, 2020 Not sure I agree. The disparity remained after the oil was squirted into the bore. A little oil may help the rings seal better but it is unlikely that the oil will significanlty seal a burned valve/seat. There may also be a ring issue as the compression went up a bit on all cylinders but 4 was still significantly lower. Here's a link from Popular mechanics explaining compression testing. https://www.popularmechanics.com/cars/how-to/a8520/cars-101-how-to-do-a-compression-test-14912158/ Quote Link to post Share on other sites
Ali King Posted October 13, 2020 Author Report Share Posted October 13, 2020 Thanks again all. Andy M: A couple of things prompted the test: It had been intermittently firing on 3 cylinders and as the car was new to me, and as I could get a compression tester very cheap, I thought I would give it a go. As it turned out the misfire was on number 1 and seemed to be due to the (right angle) ht cap touching the heater pipe, which I solved by re-routing the ht cable. However, as all the ht caps seem to be very close to the pipe I think I may swap all the ht cables with a new set which have a straight ht cap and will therefore hopefully clear the pipe. Taking onboard all the advice - I'll check the tappet clearances, drive for a bit, do another test when the engine is a bit warm. If not any better I'll might have a go at the leak down test, then if necessary head off. Alistair. Quote Link to post Share on other sites
Lebro Posted October 13, 2020 Report Share Posted October 13, 2020 (edited) 16 hours ago, Chris Hubball said: Hi Bob I am interested in your home made leak tester any chance of a brief description of how you made it, I tried to make one myself but could not find a way of sealing the tube to the old spark body. Cheers Chris Easy if you have a lathe. I took a spark plug, removed all the ceramic insides (brute force etc) leaving a hollow metal shell with a parallel inside entrance at the top. I then took a plumbing fitting of a suitable size, & reduced the out side diameter to be a tight fit in the old plug, & sealed it in with locktite. Then selected a compressed air fitting to screw & seal into the fitting. Finally removed the metal sealing ring from the plug, & replaced with an 'O' ring. Bob Edited October 13, 2020 by Lebro Quote Link to post Share on other sites
harlequin Posted October 13, 2020 Report Share Posted October 13, 2020 I picked up one of these https://www.amazon.co.uk/gp/product/B078KJPJJT/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1 which works ok, there are lots of them out there from lots of suppliers but you will need some sort of compressor George Quote Link to post Share on other sites
Ian Vincent Posted October 13, 2020 Report Share Posted October 13, 2020 2 minutes ago, harlequin said: I picked up one of these https://www.amazon.co.uk/gp/product/B078KJPJJT/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1 which works ok, there are lots of them out there from lots of suppliers but you will need some sort of compressor George That's the same as the one I have George but mine was £15 on Ebay. For what I paid for it, I'm impressed. I was expecting a load of rubbish. Rgds Ian Quote Link to post Share on other sites
john.r.davies Posted October 13, 2020 Report Share Posted October 13, 2020 1 hour ago, harlequin said: I picked up one of these https://www.amazon.co.uk/gp/product/B078KJPJJT/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1 which works ok, there are lots of them out there from lots of suppliers but you will need some sort of compressor George Aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaargh! Not the Red Box! Usually an indicator of cheap Chinese ****. Not in this case (!)? Quote Link to post Share on other sites
harlequin Posted October 13, 2020 Report Share Posted October 13, 2020 2 hours ago, Ian Vincent said: That's the same as the one I have George but mine was £15 on Ebay. For what I paid for it, I'm impressed. I was expecting a load of rubbish. Rgds Ian I'm afraid that's the story of my life Ian 1 hour ago, john.r.davies said: Aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaargh! Not the Red Box! Usually an indicator of cheap Chinese ****. Not in this case (!)? Not cheap enough as it turns out John, it has worked OK so far so maybe I have the deluxe GTI version George Quote Link to post Share on other sites
Chris Hubball Posted October 13, 2020 Report Share Posted October 13, 2020 Thanks Bob It will give me something to do and keep me out of mischief while I cannot meet with my mate in the pub. Cheers Chris Quote Link to post Share on other sites
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