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Old 03-11-2021, 06:08 PM   #1
Pleasedontletitbedead
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Question B200FT Compression

Hey guys, having a bit of a terrible time with my 940 I posted in here a while ago about having low oil pressure on my B200FT.

I know that the compression ratio on this engine is different from all the other redblock engines (8.5:1). I have no idea what the pressure is supposed to be though.

I don't know how long the car has been running low oil pressure, so I wanted to get an idea of whether it's healthy or worth saving before I waste my own time or pay some guy a fortune to screw around with the bottom end (my mechanical knowledge ends at 2 stroke dirt bikes). I bought a compression test gauge, did a dry test and my results are as follows:

CYL 1 130PSI
CYL 2 140PSI
CYL 3 125PSI (retested later, got 130PSI, retested again even later and got 125 again)
CYL 4 135PSI

Are these OK? I haven't been able to find specific or reliable information on healthy cylinder pressure for a B200FT, so I have no idea if this is OK or not. Bear in mind I want to make 200-250+HP with this engine over the time I own it.

Someone local has a spare B200FT (have not compression tested yet) and I'm wondering if I should just swap that in, or go ahead and get mine fixed.

Thanks in advance.
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Old 03-11-2021, 06:20 PM   #2
Fa182
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According to the pocket data book, the compression ratio for both the B200/230's are spec'd as 9bar or 130psi with a max deviaton of 2bar or 30psi between the cylinders.

See here: https://www.myvolvolibrary.info/Tech...DataPocket.pdf
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Old 03-11-2021, 06:29 PM   #3
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OK, so cylinder 3 is below the minimum spec but sometimes right on it... so confusing. Should I swap the engine or continue to fix the low oil pressure problem?
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Old 03-11-2021, 06:31 PM   #4
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I would say your engine is perfectly fine, but let's wait on the comments from the real experts (I'm not one of them)

Anyway, mine had almost the same results the last time I tested it (B230FT).
I'm running a bigger turbo at close to 1bar since 2 years and everything's fine.
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Old 03-11-2021, 06:42 PM   #5
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OK, thank you very much that is very reassuring. Hopefully it is worth keeping this engine and repairing the oil pressure issue then! I will wait to see what the 'experts' so to speak, say
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Old 03-11-2021, 07:13 PM   #6
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Did you hold the throttle open while doing the test? If not, you should.

Was the engine warm for the test? It should be.

How is your battery? The engine should crank 250-300 rpms during the test.
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Old 03-11-2021, 07:25 PM   #7
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Just making sure, did you hold the throttle wide open while testing compression?

I am not one of the experts you may be waiting on but I think thicker oil (if your climate permits) could help you get those numbers up. I'd also do another test with the engine hot cause everything expands and seals better, especially on these engines that are prone to piston slap.
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Old 03-11-2021, 07:28 PM   #8
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Quote:
Originally Posted by hiperfauto View Post
Did you hold the throttle open while doing the test? If not, you should.

Was the engine warm for the test? It should be.

How is your battery? The engine should crank 250-300 rpms during the test.
Saw this post right after chiming in, lol. Hiperfauto is right, you should also make sure that it is cranking nicely. Have all the plugs out and do one cylinder at a time, if you don't do it this way already.
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Old 03-11-2021, 07:42 PM   #9
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Quote:
Originally Posted by hiperfauto View Post
Did you hold the throttle open while doing the test? If not, you should.

Was the engine warm for the test? It should be.

How is your battery? The engine should crank 250-300 rpms during the test.
Thanks,

Yes, WOT

Yes, car tested with warmed up engine (idled for 10 mins, I'm not driving it because of the low oil pressure problem)

My battery is indeed in need of a replacement, but I trickle charged it for a few hours before I got these results. I didn't read the tach! I could potentially go and buy a new battery tomorrow and re-test.

Could a worn crank or bearings cause low compression?

Last edited by Pleasedontletitbedead; 03-11-2021 at 07:48 PM..
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Old 03-11-2021, 07:45 PM   #10
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Quote:
Originally Posted by daniels740 View Post
Just making sure, did you hold the throttle wide open while testing compression?

I am not one of the experts you may be waiting on but I think thicker oil (if your climate permits) could help you get those numbers up. I'd also do another test with the engine hot cause everything expands and seals better, especially on these engines that are prone to piston slap.
Thanks, I could definitely go with a thicker oil, I'm using 10w40 Magnatec, anything you recommend?

I've addressed the other stuff in my other reply
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Old 03-11-2021, 08:04 PM   #11
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I wouldn't go thicker than 10w40, although something like Engine Restore, (not sure if they have that where you live) might help the engine. I watched a video on YouTube about that stuff by Project Farm. I used to hate these types of oil additives until Marvel Mystery Oil got a sticking valve I had free. YMMV.

Also, what makes you think you have low oil pressure? Is the light coming up on the dashboard or did you use an oil pressure gauge?
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Old 03-11-2021, 08:12 PM   #12
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OK cool I'll have a look for something like that, I've heard good things about Shell Rotella.

The oil pressure is a seperate issue (I hope) Yeah flickers on at idle when the engine gets warm, checked pressure and its 7psi at idle (yikes) and goes up to about 30psi at 3k rpm. I want to know if this compression pressure is OK before I go spending money on getting the oil pressure issue fixed basically, or if I should swap a different engine in (my goal is 250ish HP built up over time) I want to get driving in it ASAP as well.
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Old 03-11-2021, 11:50 PM   #13
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Someone please correct me if I'm wrong, but you should get around 10psi per 1000rmp, so your engine isn't that bad. I just looked over your "B200FT Low Oil Pressure" video on YouTube and couldn't help but notice oil around the filler cap. In addition, at around the 1:07 - 1:10 mark in the video, I noticed smoke plume out around the engine oil dipstick. Make the video full screen and you will surely notice what I am talking about. I set the video to start right before you can see the aforementioned smoke.




No idea how much of a difference it would make for the issues you have right now, but I would definitely start by servicing the PCV system ASAP.

Last edited by daniels740; 03-11-2021 at 11:57 PM..
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Old 03-12-2021, 05:32 AM   #14
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I really appreciate you having a look at my older post and continuing to try to help me!

As far as my Haynes manual says, it should be 35-87psi at 2000rpm, which it is definitely not. It was only getting around 15psi at 2000rpm, so definitely not right. The very first thing I did when I saw the oil pressure issue was replace the oil cap seal, and the pcv system. This made the oil light not come on when the engine is cold, but it still flickers on when the oil has warmed up, I think some o rings have been blown out somewhere in the bottom end, as someone mentioned in that previous thread.

The plume of smoke is actually my breath in that video, it was -2 celcius.

As I said above my experience before this amounts to working on 2 stroke dirt bikes, and I don't have the means to work on it as I'm stuck at my parents (Corona), so I booked it into a shop a month ago and it's finally going in tomorrow.

As far as I've heard, oil pressure should not affect compression, I really hope someone responds about the compression because I just want to know if I should give up on this engine before spending a fortune on it and just get another one.

Last edited by Pleasedontletitbedead; 03-12-2021 at 05:38 AM..
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Old 03-12-2021, 10:32 AM   #15
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Quote:
Originally Posted by Pleasedontletitbedead View Post
The plume of smoke is actually my breath in that video, it was -2 celcius.
I could've sworn it came from the dipstick!

The thought didn't even cross my head, living where you don't even need a jacket during winter, lol.

Well, that's about where my expertise ends. Hope someone can help you figure it out. I'd use some engine restore and would see how long the engine fares, especially if you have another one waiting to be dropped in.
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Old 03-17-2021, 12:41 PM   #16
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Hahahaha thank you for your help!

Well I've got some good news, I took the car to my uncle, who has better tools than me. We compression tested it - 155 dry across all 4 cylinders and 200 wet, that sounds very healthy to me and is just 3% lower than the upper level of 9-11 Bar stated in my Haynes manual.

We took the sump off and found the usual low pressure issue cause - a perished O ring in the transfer pipe. Bearings checked and the engine is still healthy. The sturdy Swedish Redblock strikes again, time to turn up the boost a little bit and get the car looking clean and sitting lower.

Last edited by Pleasedontletitbedead; 03-22-2021 at 08:15 PM..
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Old 03-17-2021, 01:10 PM   #17
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Happy to hear it! If you're in to that kind of thing, you can start a project thread under "projects and restorations." I didn't when I started really restoring my 740 and regret not having documented everything I've done in a single thread.

In any case, have fun with your Volvo!!
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