what figure should a healthy engine be reading and what is the allowable variation bewteen the cylinders?
I believe that a new engine is should be about 180-190 PSI perhaps more but no lower than 140 PSI. Whats most important even more then the total compression is that no two cylinders vary by more then about 10%. Bently manual will give the proper figures for wet and dry compression tests.............I can't remeber them at the moment.
ok, my head gasket failed recently. compression test showed 195, 200, 200, 173. does this mean that in general compression is fine, more importantly bores are fine.... alls good except for minor head gasket leak?
OK Bently offically says for a 9A and PL (so I guess the same as a KR) New engines145-189 PSI (10-13 bar) Wear limit109 PSI (7.5bar) maximum 44 PSI(3bar) difference between cylinders
i was using a cheap compression tester, but was getting about 13.5 bar. not sure how accurate the readings would have been. its a pb engine. so i suppose thats ok then
Whoo hoo. Got between 180 to 190 PSI on all cylinders when I did a compression test about a month back.
I got 190-200PSI on all cylinders in my 9A. I got 150PSI on the same guage in all cylinders in my old worn KR. It's not just about the final figure but also how quickly the compression rises as you crank it. It should reach peak pressure in 3 goes really, if it takes ages to get there it points to worn rings/bores. Joe
I think I got 220psi on all cylinders in mine, 1.8 GU. That was using a 20 Gunson guage you can get from Halfords. A few q's: 1) Do they seem too high? 2) What is a high compression a sign of? 3) Is a high compression bad news? Cheers
i used one of those gunson gauges, and got 200 on all cylinders, except the one i suspect had the gasket fail on. maybe they read a bit over ??
They aren't that accurate, you are looking for a consistent reading across all 4 cylinders. A very basic rule of thumb is that if your compression reading is 16-18 times the compression ratio or above, the engine is good. 200 is fine, a good engine. If I had 109psi as per Bentley I would be scrapping the engine.......
I know this thread is 2 years old but ive just done a compression test on my Golf and looking for some figures. The figures i have i thought were a bit low be according to this thread they are ok. Thecar is an early 1.8 8v GTI (solid lifter type) and the figures i have are : 1. 145 psi 2. 135 psi 3. 140 psi 4. 145psi Does this seem to be the norm?
I did one the other day and got 149/150/150/149. These were "dry readings" with the fuel pump relay removed. Wet readings were 170ish..? Which is the correct figure bentley quotes - dry/wet?
They seem quite poor. I've got a DX engine in my Scirocco and with 135k on the clock I got 205 - 210 on all pots. 14 bar in modern money.
Don't bother disconnecting the injectors or pump relay, and make sure you do the test right - throttle wide open while you crank it. The Bentley figures are for a dry test, no oil in the bores. On an 8v there is no point doing a wet test unless you have a "spout" type oil can with a flexible nozzle, so you can direct the oil to the bore sides. Otherwise it'll just pool in the piston and give you an artificially high figure. And yep, Frank - your dry readings are pretty low. is it an 8v or 16v, and how much oil did you use for the wet test?
8v kjet engine on a scirocco. I didn't really think the figures were all that bad - but more because they were all pretty close. The engine's done 140k and still goes pretty well. I used a tsp or so of oil through the spark plug hole. How accurate are the comp testers anyway? 15 quid from halfooords cant be the height of technology eh? If they are low, what is the best course of action - if I need to do anything? I thought the fuel pump on a kjet still pumped when cranking - wouldn't the petrol give me an artificially high value. Throttle was wide open when cranking. No other problems apart from a possible blown HG(!) gotta check with a coolant tester when it comes from ebay.
I got 180`s on the 16v after stacking head gaskets, probably would have been over 200 before? (never checked..).
The figures are close, but low. I'd be looking for more around the 180 mark on that engine, dry. The oil may have made it's way round to the rings, but you really need to direct it at the bore walls on an 8v to be sure. The petrol is injected in such small amounts it won't affect the test. The equal results just mean your cylinders/rings are equally worn - which is a good thing! You don't have to do anything if you are happy with the engine, but if it's burning oil or you think it's down in power then new rings and a hone would be in order, as a minimum. You'd be surprised at the difference this makes - I did a mate's engine recently with rings and a hone, and he said it felt like it had an extra 20hp. If you've done a lot of miles in it yourself, then you may not have noticed the drop in power - and if it was like that when you bought it, then you certainly won't have noticed it because it'll have been down on power since you bought it!
I am pretty happy with the engine, but I am bothered I might be losing power. How difficult is it to fit new rings, and what tool do I need to rehone the cylinder? I guess the big end caps need taking off and the pistons popping out, but is the wear likely to be in the rings or the block? If it's in the block, it's unlikely to make much difference surely? Would "roughing up" the bores with emery cloth be good enough for the new rings to wear in? TA
