Low Compression, fix without rebuild?

12arotary · 04-07-2009, 08:38 AM

Anyone know of anything out there that will boost my compression even just a little bit? I'm now up to 224,800 original miles on my 88 and its showing just about 78 on both rotors even, It runs wonderfully its just a little difficult to start when its luke warm fine when hot just sitting hot for about ten min and it floods a lot- I'd rather just see how long it can run, I have a replacement engine ready to go in any time but its my proof tool to how long rotarys can last when taken care of

solareon · 04-07-2009, 08:45 AM

try putting in a fuel cut switch. 224k miles is pretty good but some people have gotten past 300k. There is a local guy here with over 300K on his 13b in a 1st gen. When mazda switched to the 3 piece seals you just aren't gonna get that much life out of them

12arotary · 04-07-2009, 08:52 AM

Quote:

Originally Posted by solareon

try putting in a fuel cut switch. 224k miles is pretty good but some people have gotten past 300k. There is a local guy here with over 300K on his 13b in a 1st gen. When mazda switched to the 3 piece seals you just aren't gonna get that much life out of them

I'd rather fix the problem rather than band aid it haha (fuel switch)
I think I will probably rebuild before I do that haha

and yes on the first gens 13b's lasting longer- I have an fb with 201,000 on it now and its running fine still though its a 12a so its going to end up with the housing flaking catching up with it first

classicauto · 04-07-2009, 11:01 AM

anything that's going to "fix" that problem will be a bandaid. So if you're not down for a bandaid, rebuild it

But there's really not much to do for low comp other then throwing a bunch of oil in the engine. And there's not many ways of doing that aside from dumping it inside one way or the other. As sated a fuel cut switch could allow you to prevent some of the floods, but if the comp is too low to start consisntently then there's absolutely no way around it without a bandaid.

vex · 04-07-2009, 11:12 AM

Bandaids that may or may not help:

Get injectors cleaned and flow tested.
Use heavier oil
that's about all I can think of off the top of my head.

need RX7 · 04-07-2009, 01:10 PM

I must have got lucky. My S4 n/a has 202,xxx miles and I believe the comp was at least 85 psi last time I did a test and it starts in under 3 seconds any time.

It was alot worse when I got it though, but I did alot of work to it:
- Injectors cleaned and flow tested
- All new intake and exhaust manifold gaskets
- New injector plugs (mine were all janky beyond repair)
- Emissions removal (cats, rat's nest, air pump, EGR)

I think having the injectors cleaned will help alot with the flooding. I used Witch Hunter Performance, A+ service.

rx4ur7 · 04-07-2009, 02:52 PM

Really no fix for low compression. I don't think you can even say bandaid, more like a spray of bactine maybe.

Cleaning injectors, fuel cut might buy you a few months. At least it might be easier to start for awhile. You know it is short term and you have the other motor. Drive it till it drops. You are over Mazda's projections.

Redline fuel injection cleaner. As will the cut switch. Half bottle per tank, two tanks, once a year and you should never have any injector issues. Works on all models. Also Redline formula is the only aftermarket that I know of that is approved by Mazda. Heavier oil not necessarily going to help with compression. Lighter might because you would blow by more, so more would get to the combustion chamber. Neighbors probably wouldn't like you, unless you have a mosquito problem.

Usual life expectancy in Tucson is 180K for the 2nds. Most are at replacement criteria specs at 140. Dry heat isn't kind to the round motor.

Flooder · 04-07-2009, 06:02 PM

I'd say just put in a fuel cut switch and use it to shut the car off every time. That's what I do and I never have any issues with getting it started, hot or cold. And honestly, if you aren't wanting a bandaid fix, then just rebuild the motor, because you can't raise your compression.

12arotary · 04-08-2009, 12:37 AM

I'm going to take the injectors out and have them cleaned, did it like two years ago but then I sold the car it went through three people and I bought it back so who knows what happens, though is 80 psi just too low?

and I want to put off the rebuild as long as possible cause then I loose my high mileage bragging rights, stupid reason but oh well haha
Oh and it does have all new intake gaskets and throughly cleaned intake throttle body afm and all emissions have been removed about 15k miles ago

RRTEC · 04-08-2009, 07:45 AM

Your compression may be low due to the flooding issues.... When an Rx-7 floods the fuel mixes with the oil contaminating it. I have had motor's build almost no compression due to thinned out oil. I would address the fuel system, then change the oil with a 20w50 weight and see if your compression numbers don't come back up.

12arotary · 04-08-2009, 10:49 PM

I didn't check when it was flooded, and when it floods it's just flooded for a sec I pull the injector fuse and it fires right up plus it only floods if i run it then let it sit till its not hot but its not cold otherwise it fires no problem- I just changed the oil to 5w40 and it shows a good solid 80 on all faces on both rotors-

And I'm just asuming it's low comp due to 224k miles haha

04-07-2009, 08:38 AM	#1
12arotary tumor-syphilis-itis-osis Join Date: Sep 2008 iTrader: (0) Posts: 191 Rep Power: 17	Low Compression, fix without rebuild? Anyone know of anything out there that will boost my compression even just a little bit? I'm now up to 224,800 original miles on my 88 and its showing just about 78 on both rotors even, It runs wonderfully its just a little difficult to start when its luke warm fine when hot just sitting hot for about ten min and it floods a lot- I'd rather just see how long it can run, I have a replacement engine ready to go in any time but its my proof tool to how long rotarys can last when taken care of __________________ 82 300d 82 Gsl 84 b2200 Diesel 88 gxl

04-07-2009, 11:12 AM	#5
vex RCC Loves Me Not You Join Date: Jul 2008 Location: Influx. iTrader: (6) Posts: 2,113 Rep Power: 19	Bandaids that may or may not help: Get injectors cleaned and flow tested. Use heavier oil that's about all I can think of off the top of my head. __________________ The Official FC Radiator Thread My Project Thread: Cerberus CCVT Virginia Rotary Group

04-07-2009, 01:10 PM	#6
need RX7 Clean S4 Nutswinger Join Date: Mar 2008 Location: Sterling Heights, MI iTrader: (0) Posts: 485 Rep Power: 17	I must have got lucky. My S4 n/a has 202,xxx miles and I believe the comp was at least 85 psi last time I did a test and it starts in under 3 seconds any time. It was alot worse when I got it though, but I did alot of work to it: - Injectors cleaned and flow tested - All new intake and exhaust manifold gaskets - New injector plugs (mine were all janky beyond repair) - Emissions removal (cats, rat's nest, air pump, EGR) I think having the injectors cleaned will help alot with the flooding. I used Witch Hunter Performance, A+ service. __________________ -Ted -1986 Mazda RX7 Sport [DD/beater]: engine finally let go at 205k. parts car status. -1986 Mazda RX7 base [resto-mod project]: S5 n/a swap in progress.

04-07-2009, 06:02 PM	#8
Flooder Rotary Fanatic Join Date: Feb 2008 Location: Tucson, Arizona iTrader: (0) Posts: 321 Rep Power: 17	I'd say just put in a fuel cut switch and use it to shut the car off every time. That's what I do and I never have any issues with getting it started, hot or cold. And honestly, if you aren't wanting a bandaid fix, then just rebuild the motor, because you can't raise your compression. __________________ AZRX7.COM Red 1991 A-package(SOLD) Red 1990 GXL(SOLD) White 1989 GTUs(DEAD) Red 1988 Turbo II(DD) Black 1988 Turbo II(SOLD) Rebuilt and street ported motor, Garrett T04E Turbo, 3" Turbo Inlet Duct/AEM Dry Flow Filter, Your Mom's MBC, Blitz FMIC, 890cc and 1000cc injectors, Tomei FPR, Walbro, Rtek 2.1 ECU, Taurus E-Fan, Turbonetics BOV, 3" Motoria/Corksport Turbo Back Exhaust, Emissions Removed, Greddy Boost Gauge, Megan Racing Water Temp Gauge, 5one5 Triple Gauge Pod, AEM Uego, GP Sports Body Kit, Fiber Images CF Hood, S5 Seats, S5 Tails, S5 Alt, Dual Alt Pulley, D2 Coilovers, NRG Quick Release, Shook Motorsports Radiator, HID's, AN/Steel Braided Oil Cooler Lines, SUPER JDM TYTE DRIFT BUTTON www.DensetsuMotorsports.com www.AZRX7.Com www.FloodersAdventure.com

04-08-2009, 12:37 AM	#9
12arotary tumor-syphilis-itis-osis Join Date: Sep 2008 iTrader: (0) Posts: 191 Rep Power: 17	I'm going to take the injectors out and have them cleaned, did it like two years ago but then I sold the car it went through three people and I bought it back so who knows what happens, though is 80 psi just too low? and I want to put off the rebuild as long as possible cause then I loose my high mileage bragging rights, stupid reason but oh well haha Oh and it does have all new intake gaskets and throughly cleaned intake throttle body afm and all emissions have been removed about 15k miles ago __________________ 82 300d 82 Gsl 84 b2200 Diesel 88 gxl Last edited by 12arotary; 04-08-2009 at 12:40 AM..

04-07-2009, 08:45 AM	#2
solareon The Newbie Join Date: Jun 2008 iTrader: (0) Posts: 5 Rep Power: 0	try putting in a fuel cut switch. 224k miles is pretty good but some people have gotten past 300k. There is a local guy here with over 300K on his 13b in a 1st gen. When mazda switched to the 3 piece seals you just aren't gonna get that much life out of them

04-07-2009, 02:52 PM	#7
rx4ur7 Rotary since 1972 Join Date: Nov 2008 Location: Tucson iTrader: (0) Posts: 231 Rep Power: 17	Really no fix for low compression. I don't think you can even say bandaid, more like a spray of bactine maybe. Cleaning injectors, fuel cut might buy you a few months. At least it might be easier to start for awhile. You know it is short term and you have the other motor. Drive it till it drops. You are over Mazda's projections. Redline fuel injection cleaner. As will the cut switch. Half bottle per tank, two tanks, once a year and you should never have any injector issues. Works on all models. Also Redline formula is the only aftermarket that I know of that is approved by Mazda. Heavier oil not necessarily going to help with compression. Lighter might because you would blow by more, so more would get to the combustion chamber. Neighbors probably wouldn't like you, unless you have a mosquito problem. Usual life expectancy in Tucson is 180K for the 2nds. Most are at replacement criteria specs at 140. Dry heat isn't kind to the round motor.

04-08-2009, 07:45 AM	#10
RRTEC Rotary Fan in Training Join Date: Feb 2008 Location: Spring hill TN 37174 iTrader: (-1) Posts: 57 Rep Power: 17	Your compression may be low due to the flooding issues.... When an Rx-7 floods the fuel mixes with the oil contaminating it. I have had motor's build almost no compression due to thinned out oil. I would address the fuel system, then change the oil with a 20w50 weight and see if your compression numbers don't come back up.

04-08-2009, 10:49 PM	#11
12arotary tumor-syphilis-itis-osis Join Date: Sep 2008 iTrader: (0) Posts: 191 Rep Power: 17	I didn't check when it was flooded, and when it floods it's just flooded for a sec I pull the injector fuse and it fires right up plus it only floods if i run it then let it sit till its not hot but its not cold otherwise it fires no problem- I just changed the oil to 5w40 and it shows a good solid 80 on all faces on both rotors- And I'm just asuming it's low comp due to 224k miles haha __________________ 82 300d 82 Gsl 84 b2200 Diesel 88 gxl