Low compression 1990 6 bolt

[blakkat]

Well I did a compression test on the car and got the following results

Cylinder 1 - 105psi
Cylinder 2 - 95psi
Cylinder 3 - 115psi
Cylinder 4 - 115psi

Didn't have a chance to do a leak down or a wet test. However I noticed the car feels very laggy for a 14b so I checked the cam timing to make sure it wasn't off a tooth, here's what I got

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Just wanted someone to check it over but it looks good. So am I looking at getting a new motor now?

 

[BogusSVO]

The cam marks look good, how are the crank marks?

You may not need an engine or rebuild at this time, a few more tests will let us all know more.

Do a leak down test next.

You may have jumped a tooth or two at the crank, you may have slightly bent valves, or a compression blown HG, OR the engine is just wore out and needs rebuilt.

 

[blakkat]

Will there be a mark on the crank pulley or am I going to have to take the timing cover off to see? Sorry I'm not exactly the Most knowledgable person on the 4g63 yet. I don't think it's a head gasket, no white smoke, bubbling coolant etc. ill see if they'll let me do a leak down at school.

 

[BogusSVO]

You can still have a blown HG with out white smoke.

A compression blown HG, allows the compression to swap between to ajoining cylinders.

A coolant blown HG allows compression to go from the cylinder to the water jacket.

Yes you should have a mark on the H-Bal and a mark on the cover to show TDC

 

[blakkat]

Yeah true, ill have to double check everything I'm just concerned more about the overall low compression rather than the difference between cylinder, which led me to check timing to begin with, I'll check back with a picture of the harmonic balancer when I leave to school . Thanks I appreciate the help

I mean this car is really slow due to this problem i think. It's reasonable to expect a 1990 6 bolt with 2g maf, intake, turbo back exhaust, evo injectors, and a tune to beat a 2011 Mitsubishi lancer non turbo .

 

[Yourself]

My first dsm did the exact same thing, except it didn't seem to lag much, just lacked performance.

It was a headgasket on mine. From having a bad one for so long the head was warped... So I planned the head. After I did this compression was slightly higher then stock (for obvious reasons) and she ran like a champ!

 

[miloolim]

If you can weld and have a air compressor you can make your own leak tester out of a old spark plug....

 

[blakkat]

No access to a welder :/
and yeah the car is really slow, my speed3 feels like a ferrari compared to the talon right now. anyway here's a picture of the crank pulley

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Thanks for the help guys I appreciate it

 

[miloolim]

So did your tensionergo out and it jumped time and smack a valve? How mechanical are you? Its really not that bad. Good time to go throgh you head. Reseat your valves, check the guides, replace your valve seals and do a new timming belt. Whats nice your motor doesnt have to come out.

 

[campos_racing]

I think you might want to check that tensioner. I didnt get it till the 3rd time. Luckily i didnt harm anything valves wise.

 

[BogusSVO]

With the timing marks all lined up proper.

Next is do a leak down test.

 

[blakkat]

I just bought the car a month ago, I'm not sure why the compression is low, I'm checking timing because if its off I know it can lower compression.

I'm trying to figure out if I have worn rings, bad valve seats, guides, or head gasket. I'm pretty well mechanically inclined, never torn a motor down in any of my cars but I've pulled transmissions, and done lots of other miscellaneous things. However I have done tear downs at school just never on a live vehicle

I'm currently at uti so I'm learning more day by day. I just don't have a garage at the moment to pull the motor so if it needs a full rebuild I either will have to beg my friends to let me use their garages or i may have to just suck it up and sell the car and look for one with a motor that's in better condition.

Also ,SVO thanks that's was gonna be my next step, we have leak down testers in the shop at school, just need to find time to do it inbetween labs

 

[miloolim]

Thoes tensioners go bad so dont forget to check it.... You prob just nicked a valve.

 

[blakkat]

But the timing marks are all lined up, and the belt has good tension, is it still possible that happened given that information?

 

[miloolim]

No, it porb didnt hit the valve if everything is ok on the timming side. Sorry, my bad, I missed that.

 

[blakkat]

It's alright, yeah I'm debating. Just hoping its somewhere in the head and not the bottom end. I can rebuild the head without too much of a problem but the bottom end is a different story, just don't have the resources at the moment

 

[miloolim]

Did you run it out of oil? If not leak test it. Watch this 2 MINUTE TECH | PowerBlocktv.com

 

[blakkat]

I haven't, I will entertain the possibility that the previous owner may have however. I will watch the vid as soon as I'm out of class

 

[miloolim]

right on!

 

[Cody Nelson]

timing wont affect compression while doing a test. and if it was a bent valve there will be almost no compression in that cylinder due to the valve never seating. you either have compression or you don't. its really tough to say because it can be any of the listed above. i would pull the head, inspect valves and seats. once all proves promising in the head check the gasket. my guess is that it is fine. the motor is 22 almost 23 years old with god knows how many miles on it. its tired and ready for a rebuild. ill be its the rings and bad cylinder wear :/

 

[BogusSVO]

timing wont affect compression while doing a test. and if it was a bent valve there will be almost no compression in that cylinder due to the valve never seating. you either have compression or you don't. its really tough to say because it can be any of the listed above. i would pull the head, inspect valves and seats. once all proves promising in the head check the gasket. my guess is that it is fine. the motor is 22 almost 23 years old with god knows how many miles on it. its tired and ready for a rebuild. ill be its the rings and bad cylinder wear :/

Ignition timing will not affect a compression test, But if the timing is off between the cams and crank it will. Beacuse that will affect the cams open and close point reltive to the crank.

 

[blakkat]

Thanks SVO, haha. Yeah well we know its not that. A buddy at school is gonna let me use his leak down tester this weekend probably

 

[blakkat]

Alright so cylinder with 95 psi had 40% leakage. Others had 35% and one was at 10% and I could hear air coming from the dipstick on each one except the 10% so it's safe to assume I need a bottom end

 

[BogusSVO]

Sounds like it.

Now the question is, you going to buy s shortblock? or Build the one you have?

 

[blakkat]

I'm wondering if its worth the trouble honestly, I've heard a few things about me needing a full wiring harness swap, the rear end is going out so I would also need a 4 bolt swap. Would it be more cost affective to get rid of it and look for a 1gb? Or a 91 1ga?

The big plus here is its a pretty clean body, very very minimal rust here's a few pictures the previous owner sent me before I bought it

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Now I gotta fix the ebrake cable , it got stuck or a caliper locked up last night? Not sure which