|
|
|
Just did compression check on engine. Cylinders 1,2 and 3 at 195lbs; #4 close at 200lbs, maybe 199. I know it's good the results are fairly even, but what is the good expected/hoped for compression specs? Can't seem to find specs in my Bently manual. Thank you.
1989DL wagon, non-turbo, approx. 255k miles.
|
|
-
|
|
|
That is close to what I got last time I checked the 83 (at about 150k mi). It has the first edition of the B23F with 10.25 comp. ratio. I later had the head off for other reasons and there was not much in the way of deposits in the chambers or on piston tops. And there shouldn't be with unleaded, high-detergency fuel, and electronic fuel injection.
Your numbers seem somewhat high for a B230, so possibly gauge inaccuracy or some carbon in the chambers. But the important thing is consistency between cylinders and you have that, so no worries. I would stay away from any attempt to remove carbon by pouring anything into the engine. If it runs OK and gets decent fuel economy, leave well enough alone.
--
Bob: Son's XC70, daughter's 940, my 81 and 83 240's, 89 745 (V8) and S90. Also '77 MGB and some old motorcycles
|
|
-
|
|
|
Water torture, like the rope trick for blocking the crank, is a pretty harmless way to remove carbon build up that seems to have about 50/50 success rate. You just have to follow the instructions and use some common sense.
That being said, I think everyone has said what you said...sounds like the gauge or methodology are most likely at fault with the results still being fine.
|
|
-
|
|
|
I got well over 200lbs on all cylinders on my 84 years ago. My other car is a 51 chevy with 6.5 to 1, so maybe my gauge gets wacky in the higher end. It seems plenty accurate down lower, numbers-wise.
I do Italian tune-up all the time. Recently hauled 1800 pounds of concrete in my box trailer for 50miles. I stayed out of overdrive so RPM was up there. Kind of a Grandpa Italian tune-up, huh? It's been fine for years, now. If it's not pinging I wouldn't worry.
Steve
|
|
-
|
|
|
Those numbers seem high to me, but it depends on how you do the testing. Engine warm or cold? Throttle open? How many strokes of compression do you give it?
Because there are those variables the most important thing (IMO) is to be consistent so the results are obtained from nearly identical procedures with each cylinder. The numbers are more of a comparison rather than a goal.
Randy
|
|
-
|
|
|
Engine was cold, about 4-5 strokes each cylinder. Didn't open the throttle. I will mention the bricks engine runs very smooth; I just was curious what a compression test would 'say'.
It was also good to see that the spark plugs looked really good, nice 'color', gap was still fine; had about 18k on the plugs (Bosch SILVER plugs).
Aren't there "specs" in a manual somewhere that might say what the "good" numbers are, other than being consistent?? If the 195 seems "too high" what might be the issue giving/making readings like that?
One thing is that i have been very regular in doing routine maintenance of the engine, ie: oil/filter changes, tune-ups, etc. for the 9 years we have had the brick.
|
|
-
|
|
|
"Too high" compression if real will lead to excessive pinging and the need to use premium fuel at all time. The knock sensor would be constantly retarding time to account for almost constant tendency to pre-ignite.
My first assumption is the gauge is off or the testing method was flawed. The last possibility is that it has be driven by an old lady only on Sundays 3 miles to church and back. Never rev'ing an engine and never allowing it warm up will lead to carbon build up which can lead to high compression.
An Italian tune-up may be in order! If not, water torture!
|
|
-
|
|
|
I have always used only premium fuel. I also add a bottle of Techron occasionally. The brick never "pings"; I do warm up the engine; we drive about 9k-10k year, 50% freeway driving at 65-70mph. Tune up, as well as oil changes are kept up; only Bosch spark plugs, etc..
Finally found a long time Volvo mechanic says new engine is about 185, mine might have some carbon build up on top of pistons for some reason, so adding a little more Techron, otherwise seems to drive very smooth. Will re-test in about 6 months.
Thanks for your input.
|
|
-
|
|
|
" mine might have some carbon build up on top of pistons for some reason"
Two words...water...torture. Do a search but it is virtually zero risk, zero cost and might do something.
Two other words...different gauge. Whenever a reading is that unusual, the first thing to do is re-test with the instructions in front of you. The second thing to do is re-test with a different tool. Multimeters are my favorite example.
|
|
-
|
|
|
Since the ECU (or is it ICU?) retards timing when pinging starts to occur, there shouldn't be any need to go to higher octane.
"A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency" (from Wiki "compression ratio")
--
1980 245 Canadian B21A with SU carb, M46 trans, 3:31 dif, in Brampton, Ont.
|
|
-
|
|
|
It is the ICU but there are limits to how far it can retard timing. The OP wanted "potential" effects of too high a compression and the need for higher octane fuel is one of them.
|
|
-
|
|
|
The Bentley manual only gives minimum values for compression pressure: 128 psi for the B23F, B230F and B21F-T, and gives the maximum difference between cylinders -- 28 psi.
|
|
-
|
|
|
Seems high. What I have seen is 130-160.
--
Post Back. That's whats makes this forum work.
|
|
|
|
|
