Compression test woe
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Category: Technical & Model Specific Forums
Forum Name: BMW 3 Series
Forum Discription: This forum will deal with any issues on the BMW 3 Series (E21, E30, E36, E46, E90, E91 & E92)
URL: http://www.bavarian-board.co.uk/forum_posts.asp?TID=14012
Printed Date: 02-May-2024 at 19:35
Topic: Compression test woe
Posted By: orkboss
Subject: Compression test woe
Date Posted: 02-February-2005 at 08:42
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The results of a compression test on my M40 engine were as follows; Cylinder 4 : 160 Psi Spark plug Light Brown. OK Cylinder 3 : 158 Psi Spark Plug Light Brown. OK Cylinder 2 : 100 Psi checked twice Spark plug Red light Brown Tested with little oil poured into spark plug 150 PSI. Oh dear Cylinder 1 : 195 Psi Spark plug Light Brown. Trouble
My head is very noisey which could be worn cam or valve. This would coincide with the high reading of cylinder 1. Cylinder two had no oil on the spark plug it was clear and there is no blue smoke from the exhuast. Do you think the low reading which improves with oil could be accounted for by something else? |
Replies:
Posted By: Madrab
Date Posted: 02-February-2005 at 10:20
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Doing a compression test is proving that the compression rings are ok and that the valves are seating correctly. In my experience, and I hate to say it, if ur no2 cylinder is down on compression and adding oil then raises the compression then it may point towards a bad, siezed or broken ring/s or worst case, worn cylinder (hope it's not this - rebore and new rings). If it didn't rise with the oil added, then it would normally point to a valve/valve train issue. Though with an M40 stock average of 145 - 160 psi then your no 1 cylinder does sound like a valve train issue. Hope it's not too bad. Have you taken off the rocker cover and checked the cam and followers for visual wear as you may just have a goosed/siezed hydraulic lifter on number 1? Rob ------------- 1990 E3o 325i Touring and she's definately a she! Pain in the ass sometimes but goes like a bunny :oD |
Posted By: orkboss
Date Posted: 05-February-2005 at 03:50
| If I ignore it will it go away. |
Posted By: orkboss
Date Posted: 15-February-2005 at 17:35
| I checked the cam and there was no wear. |
Posted By: Peter Fenwick
Date Posted: 16-February-2005 at 04:33
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LOL...It would be nice if life was like that wouldn't it ------------- Entering an age of Austerity and now driving a Focus Diesel. |
orkboss wrote:
Posted By: Madrab
Date Posted: 16-February-2005 at 07:42
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It sure would. All the information unfortunately points towards a cylinder based problem with no 2, pants!! No1 sounds like it may be able to be fixed by replacement of the lifter but it could also be a sticky or problem valve/guide if the cam is clean. Sometimes they free themselves up but if not it could cause big problems if it sticks open. With No2 being the way it is it sounds like a strip and investigate unfortunately, if you want to go there. Rob ------------- 1990 E3o 325i Touring and she's definately a she! Pain in the ass sometimes but goes like a bunny :oD |
Posted By: Doive
Date Posted: 16-February-2005 at 07:47
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That definitely sounds like piston rings to me on number two. Could number one be a seriously gummed up combustion chamber? It may be more economical in the long run to pull the engine and put in a second hand unit, depends what the diagnosis is of course. Mine is in having the compression checked at the moment, hoping for a low reading on two cylinders to prove it is the head gasket that has blown and not anything more sinister!! ------------- 1987 BMW 525e Lux Auto (sadly deceased) http://www.getfirefox.com - Get Firefox - Ditch Hopeless Inertnet Exploder http://www.doive.co.uk - www.doive.co.uk 
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Posted By: orkboss
Date Posted: 18-February-2005 at 16:15
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There is a tapping noise especialy on cold start but it doesnot sound like the usual worn valve cam noise (I know because of my other BMW and every other m40 BMW that you see or rather hear. It seems the tapping varies in cycles going quiet for 4 second then building up in volume for 7 seconds before going quiet again.
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