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#1 HomeBuiltByJeff

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Posted 05 October 2017 - 11:42 AM

Hey guys,

 

I am starting to have a look at the engine I have that came with my car. It is an L28 90a block. It had all of the external components stripped off of it so it was basically a complete long block. 

 

I have it out and on the engine stand, and I tried to do a compression test (using a breaker bar). I can hear it sucking and blowing through the inlet and exhaust ports. I tried it on every cylinder and got 0 on all of them. It is an unknown engine, but the fact that there is zero is odd to me. I can understand 1 or 2 cylinders being low, but all of them??

 

I took off the rocker cover and the Cam gear is set up on the mark 1, and the chain feels like it has reasonable tension (although I don't really know what I am looking for). The timing seems like it is correct, as when the cam gear is on the correct mark for TDC, piston one is also TDC, so that is correct.

 

I know I have a lot more research to do, but I am wondering if anyone has some suggestions?

 

Thanks,

 

Jeff



#2 Bonkers

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Posted 05 October 2017 - 12:28 PM

I would be having a look at the valves (exhaust). Easy way to test this is to turn the engine over by hand with the plugs out in and then with them out . If there is not much difference you need to take the head off . Look for small tell tail marks on the piston where the exhaust valve may have made contact . If the engine head has been shaved or has flat top pistons in it and it has over revved say missed a gear .There is a good chance you have a stretched timing chain .They can behave a bit like a rubber band with sudden high rpm. Over 30 years at the track I have done this a few times now . The engine will idle but only above 3500 rpm and have no to very little  power.    It means you have 6 bent valves.


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#3 CBR Jeff

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Posted 05 October 2017 - 01:38 PM

Jeff remember you may need to rotate the engine through 4 revolutions to get a reading on one cylinder!

To check TDC check the position of the two cam lobes for number 1 they should both be pointing upwards ie the valves are closed.

It would be unlikely that you have no compression in all cylinders (I think).

 

Jeff


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#4 HomeBuiltByJeff

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Posted 05 October 2017 - 02:05 PM

I would be having a look at the valves (exhaust). Easy way to test this is to turn the engine over by hand with the plugs out in and then with them out . If there is not much difference you need to take the head off . Look for small tell tail marks on the piston where the exhaust valve may have made contact . If the engine head has been shaved or has flat top pistons in it and it has over revved say missed a gear .There is a good chance you have a stretched timing chain .They can behave a bit like a rubber band with sudden high rpm. Over 30 years at the track I have done this a few times now . The engine will idle but only above 3500 rpm and have no to very little  power.    It means you have 6 bent valves.

The engine doesn't offer a great deal more resistance with the plugs in. It is definitely too easy to turn. There is quite a bit of rust on the last 2 cam lobes, or the flat, unlobed area of them at least. When they get to the lobes themselves they look OK. 

 

I suppose I now have no choice, but to take the head off and have a further look. As I mentioned, with the cam chain, it is set on position 1, so if it is slightly stretched, I could move it to 2 or 3.

 

If it is bent valves, I think I will be on the hunt for another L28. I can't justify the cost to full rebuild the dead engine at this stage.

 

Jeff remember you may need to rotate the engine through 4 revolutions to get a reading on one cylinder!

To check TDC check the position of the two cam lobes for number 1 they should both be pointing upwards ie the valves are closed.

It would be unlikely that you have no compression in all cylinders (I think).

 

Jeff

Yep. Definitely TDC. Cam lobes are up and the piston (you can see it through the spark plug hole, is all the way up as well. 

 

Thanks guys.


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#5 GregTas

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Posted 05 October 2017 - 05:40 PM

Put some oil down the plug holes and see how it goes.

 

You may find at the slow speed you are going and on a dry engine the leakage is quite high. Cranking speed makes a difference on the reading on the gauge so hand speed could be the issue.

 

Engine could be tried, but unlikely all valves stuffed


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#6 HomeBuiltByJeff

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Posted 05 October 2017 - 09:30 PM

Put some oil down the plug holes and see how it goes.

 

You may find at the slow speed you are going and on a dry engine the leakage is quite high. Cranking speed makes a difference on the reading on the gauge so hand speed could be the issue.

 

Engine could be tried, but unlikely all valves stuffed

I put a teaspoon or so of oil in each plug hole and left it 15 minutes or so before I tried it. I can imagine the speed I am cranking it would make the reading a bit less, but should it be zero??

 

I am starting to think I may do a full rebuild on this engine anyway. After dealing with Porsche stuff for so long, I am amazed at how cheap rebuild parts for these cars are (no exagerration 1/10th of the price). I have no idea what I am doing, but I love a challenge, so here we come  >:D



#7 GregTas

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Posted 05 October 2017 - 09:55 PM

Perhaps the pistons aren't in there. :D

 

If I was going to the effort you are to rebuild the car I think a rebuild would be a definite for nice reliable smoke free car.

 

An L series is a simple engine and so not a hard job if you have a bit of an idea and ok on the tools. It could be as simple as bore out, check crank, get new pistons, bearings and gaskets and throw back together. Another little video episode for you  :)


Edited by GregTas, 05 October 2017 - 09:57 PM.


#8 Linton

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Posted 06 October 2017 - 03:42 AM

forgive me for being so old, but i have never heard nor tried doing a compression test by winding over the engine by hand, hook a battery up to the bastard and test it properly.


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#9 daretobedifferent

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Posted 06 October 2017 - 07:59 AM

Jeff as Linton said, you won't be able to test for compression via hand cranking it (unless you can turn the engine as fast as a starter motor which is usually a few hundred rpm).

 

The good thing is, the engine is turning over so it should be able to run. I'd hook up the starter and a battery and you should be good to go. The only thing is, you'll have to take it off the engine stand to do so. 



#10 260DET

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Posted 06 October 2017 - 08:28 AM

Just strip the engine and refresh it seeing that the rest of the car is so nice, it may not need a rebore and new pistons, just a light hone and new rings and bearings. Depends what the car is going to be used for of course.


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#11 HomeBuiltByJeff

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Posted 06 October 2017 - 09:33 AM

forgive me for being so old, but i have never heard nor tried doing a compression test by winding over the engine by hand, hook a battery up to the bastard and test it properly.

Unfortunately the engine is on the engine stand so I would have to take it off to test it. Although I do have the flywheel and the starter motor, that came with the car, it didn't come with any of the nuts bolts, so I am going to have to track something down on that front.

 

I am going to pull the head off today, and see what is going on inside. We can go from there. 



#12 gav240z

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Posted 06 October 2017 - 06:34 PM

Might be creating unnecessary work for yourself, the good news is you can still find running L-series relatively cheaply. If it has a P90a cylinder head it's worth keeping. They are getting more difficult to find and were always regarded as 1 of the better heads from factory (provided they have higher comp).


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#13 Howdy

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Posted 06 October 2017 - 07:22 PM

G'Day Jeff, the L series is about 10 X easier than the Porsche motor you pulled apart. Rip it apart Mate, not worth whacking back in now you have it out. Even if it's good, get a full gasket set, give it a quick hone by hand, new rings and bearings, maybe a cam chain and lap the valves in. It's very cheap and easy and any questions I'm sure we can answer them for you. If the motor is bad, you'll be glad you didn't whack it back in. Also I don't think anyone can get compression by hand, except maybe Arny Swarthisnickers. One option is to do a leak down test if you can get hold of a tester as you can do this on an engine stand. Or put each cylinder at EXACTLY TDC and put 100PSI into it, maybe using your compression tester hose, then see where it leaks out (rocker cover breather, exhaust or intake). You will soon see where the compression is going. You should just get a little leakage out the rocker cover breather - similar amount for each cylinder, which is leakage past the rings and none past the valves. The rusty cam might be an insight into what the bores are like. The cam should just be brownish colour on the base circle.


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#14 HomeBuiltByJeff

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Posted 07 October 2017 - 07:08 AM

G'Day Jeff, the L series is about 10 X easier than the Porsche motor you pulled apart. Rip it apart Mate, not worth whacking back in now you have it out. Even if it's good, get a full gasket set, give it a quick hone by hand, new rings and bearings, maybe a cam chain and lap the valves in. It's very cheap and easy and any questions I'm sure we can answer them for you. If the motor is bad, you'll be glad you didn't whack it back in. Also I don't think anyone can get compression by hand, except maybe Arny Swarthisnickers. One option is to do a leak down test if you can get hold of a tester as you can do this on an engine stand. Or put each cylinder at EXACTLY TDC and put 100PSI into it, maybe using your compression tester hose, then see where it leaks out (rocker cover breather, exhaust or intake). You will soon see where the compression is going. You should just get a little leakage out the rocker cover breather - similar amount for each cylinder, which is leakage past the rings and none past the valves. The rusty cam might be an insight into what the bores are like. The cam should just be brownish colour on the base circle.

That all makes great sense. I wish I had read this earlier as I definitely would have tried using compressed air in each of the cylinders, but I have now taken the head off. It doesn't look too bad in there. The bores look OK at this stage, just a hone may sort them out. There doesn't appear to be any valve contact with the pistons, so over all it looks good.

 

The main concern is with all of the water galleries which are clogged with white powder. I assume it is mostly dried coolant etc, but it definitely needs a thorough flush out. 

 

I am now thinking I will do a complete rebuild. Like you have said, it is a really simple engine, and a replacement is cheaply available if I screw it up ;) 

 

The video is out now so have a look and let me know what you guys think.

 



#15 GregTas

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Posted 07 October 2017 - 07:39 AM

Another nice video :)

 

I bet you're glad you pulled the top off now and had a look.


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#16 dat2kman

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Posted 08 October 2017 - 10:32 AM

Whioe on an engine stand,
Of the two full rotations of the drank, only half of one of those rotations, will be the compression stroke, of the piston.
Rings will never fully seal, you cant rotate it fast enough.

To try to get a rotation figure on a screw in Comp guage, remove all plugs, and ALL intake and exhaust rocker arms, and, using a rattle gun, with 27mm socket, rotate, at least 1/2 dozen times, per cylinder count No of seconds of rattle gun, use same count for each cyl.
By removing all rocker arms, every upwards stroke is a Comp stroke, and each time, the guauge needle will hold on its stop, (if fitted)
This wont be a true indication but gives indication of difference.
Then put 20-30ml of gear oil (90 weight) in the bore, test again. Incresed readings indicate ring/bore wear ( it's a very rough method!)
The 90 weight helps seal the rings.

Bit more complicated is a Leak Down test, this gives better idea of ring condition, and valve sealing, and, if coolant in system, any head gasket issues.

#17 HomeBuiltByJeff

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Posted 08 October 2017 - 12:41 PM

To try to get a rotation figure on a screw in Comp guage, remove all plugs, and ALL intake and exhaust rocker arms, and, using a rattle gun, with 27mm socket, rotate, at least 1/2 dozen times, per cylinder count No of seconds of rattle gun, use same count for each cyl.
 

I did try to rotate it with a rattle gun, but it just tightened the bolt, it wouldn't actually turn the crank. Now I have pulled it apart, I am going to do a full rebuild, so we will see how it goes.


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