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Is It Safe To Do A Compression Test With A Broken Oil Pump?

Blackkers

By Blackkers,
in Engines & Forced Induction

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Blackkers Experienced

Blackkers

Posted
Posted

I'm currently working on an old R32 GTR with a busted oil pump. It's one of the early models which were notorious for this problem. It starts but never build oil pressure, or so I was told. I haven't attempted to start it myself obviously.

I dropped the oil and it seems fine, no bits and pieces in there; I'm also going to cut open the oil filter and I'm expecting a few chunks of debris. What should I see if the oil pump has kicked the bucket?

I want to do a compression test to make sure the cylinders themselves are okay before I pull the motor out. I plan to change the oil pump and check the bearings to see if they are f**ked too which is more than likely.

So my question is, if the bearings ARE okay (unlikely), would I be doing any damage to them by running a comp test while the oil pump is 100% f**ked? With all the plugs out there isn't much load on the bearings other than on the cylinder being tested.

Any input would be appreciated thanks fellas.

Also if you have any tricks to help get the motor out you might save me a few headaches! I'm planning to leave the trans in. Leave the power steering and AC pumps in but zip tied out of the way, pull the driveshafts then everything else etc.

Ben C34 Grand Master

Ben C34

Posted
Posted

It can't be nice on the bearings, but the damage is likely already done. Especially as the engine obviously was running to break the pump!

I don't think it will be catastrophic to do the comp test.

It's alot of work removing and refitting the engine without a freshen up. I understand you only want to do do the minimum, and hopefully you can, it's just that a comp test won't tell you if the engine engine is smoky.

How about you do something real crazy and replace the pump with the engine still In the car. My theory is (it is early and I'm tired) you should be able to by just splitting the sump off and dropping the sump down a touch. Leaving everything else still connected. Sounds mental now that I wrote it , but I would still look into it.

Blackkers Experienced

Blackkers

Posted
  • Author
Posted (edited)

that's definitely a possibility, someone else mentioned that before I think. I'm pretty sure to get the sump off completely is a motor-out job. Or maybe its possible with a bit of swearing and skinned knuckles.

If the bearings are toast the motor has to come out anyway. I don't really want to attempt to pull the crank while upside down! haha what a mess.

I just pulled the plugs and put some WD40 then some oil in each cylinder and gave it a crank. It spins up fine, sounds a bit grindy but that could be normal.

I'll head off and borrow a comp tester but even if the result is positive it doesn't instantly rule out every problem as you said. Cheers for the input

Do a leak down test first, then go from there. You only have to turn the motor by hand a couple of revolutions to do it.

Sorry missed your post, I'll look into it. I don't have a tester so I'll have to ring around. but definitely a full leak down would be more appropriate

Edited by Blackkers
Blackkers Experienced

Blackkers

Posted
  • Author
Posted

It can't be nice on the bearings, but the damage is likely already done. Especially as the engine obviously was running to break the pump!

I don't think it will be catastrophic to do the comp test.

It's alot of work removing and refitting the engine without a freshen up. I understand you only want to do do the minimum, and hopefully you can, it's just that a comp test won't tell you if the engine engine is smoky.

How about you do something real crazy and replace the pump with the engine still In the car. My theory is (it is early and I'm tired) you should be able to by just splitting the sump off and dropping the sump down a touch. Leaving everything else still connected. Sounds mental now that I wrote it , but I would still look into it.

I'm definitely going to have a go at changing the pump with the motor still in the car. See how far I get before I'm back asking for help again haha

89CAL Grand Master

89CAL

Posted
Posted

You wont know if the bearings are any good till you pull the engine. If you pull the engine it wont take much to pull the head and look at the bores (which if it was me I'd be doing anyway, unless you have a borescope to do it without pulling the head)

If your at that stage, you may as well replace rings + hone the cylinders (or further repair)

I dunno, maybe I'm not getting it. But if it was me I'd be stripping it as a precaution if nothing else. Best case scenario is a couple of rings, honing cylinders and new bearings. Worst case sceneraio you'll need some new pistons etc. But at least then you will know for sure its not going to fail

Blackkers Experienced

Blackkers

Posted
  • Author
Posted

Yeah you're exactly right. I do have a 2nd car at the moment too.

I would love to get the engine on the stand an do it properly, fresh rings, honed bore and fresh bearings, new oil pump and crank collar, HG. timing belt etc. Sounds good!

Changed my mind again haha I'm just going to pull the damn thing out and do it properly. If I went to the effort of changing out the pump and it spins a bearing by the end of my street I wouldn't be happy

Blackkers Experienced

Blackkers

Posted
  • Author
Posted

I didn't realise the passenger side drive shaft was a half shaft. That side was easy to undo. Can I leave the half shafts in and just unbolt it?

Also is there a trick to removing the drivers side shaft?

doo doo Proficient

doo doo

Posted
Posted

Yep take the top fill plug out of the front diff and lever the shaft out from the middle of inside the diff with a large screw driver or similar. If thats too fiddly then drain the diff oil and take the cover off to do the same. Ive tried pulling it from the driveshaft side but never had success. You also wont get the engine out if you leave the driveshaft there so you also need to remove the shaft completely before lifting the engine out, or at least unbolting the hub enough to swing it out of the way. Which you have to do anyway to remove the driveshaft.

Have fun.

Blackkers Experienced

Blackkers

Posted
  • Author
Posted

thanks man, i got the RHF shaft out using a big screwdriver...it was missing the surclip on the diff end.

i unbolted the passenger side but left it in, my next day off is wednesday ill pull it out then, thanks for the heads up i was about to leave it in

89CAL Grand Master

89CAL

Posted
Posted

yeah put a jack under the transmission (mainly for safety) and undo the transmission mount. Then let the jack down, make sure the thing doesnt just tilt back, shouldnt do but just in case (safety first) then work out a way to lever the engine/gearbox to tilt it a bit then you can get a long long extension along the gearbox to get the bolts

It's much easier to do this with more than one person

Blackkers Experienced

Blackkers

Posted
  • Author
Posted

awesome thanks for that, I've got saturday off so ill get at it then. Then it's time to pull the engine finally.

I was considering doing the opposite and jack up the rear of the gearbox to reach the bolts down the back of the firewall but theres no way that's easier

I picked up an R34 rb25det neo oil pump today. supposedly these are the same as the N1 units, should do the job

doo doo Proficient

doo doo

Posted
Posted

As mentioned, a couple of long extensions. I put a flexi joint at the socket end also. Be aware as you drop the gear box down it weighs about 90 kgs. You also need to twist it clockwise (when facing front) before sliding it back to to allow the starter motor hump-housing to clear the body. Dont drop it on yourself- have another person to help (plus a couple of jacks), it will be a lot easier. Also undo the tailshaft flange off the box to allow it to drop enough and slide backwards. Make sure its a push type box and clutch still (if its pull type you need to release the throw out bearing before the box will come off). You might find it easier to get the engine out if youve taken the clutch off as well, and dont forget to remove the gearstick before dropping the box.

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