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What did I do wrong assembling the big bore b20?

gsellstr said:
I would like to see them up around 170, but as John mentioned as well, the bigger concern is the spread between them. Cam timing won't cause that kind of spread between cylinders usually.

If the motor is fresh, there's a chance things are fully seated yet. The oil test John mentioned will help you ID if the rings haven't seated yet.
Click to expand...

Yea the spread had me worried.

I was just cranking the engine cold, with a jump pack on the battery to prevent any miss readings from a dying battery.

When I get a chance to run back to the garage, the plan will be to run it up to temperature, redo the valve lash and run a compression test again.
 
oemoilleaks said:
You're the second person to suggest the spark jumping. How did you go about repositioning the optical sensor?
Click to expand...

I was using a Mallory dual point distributor body, and the Crane optical box I was using was old and used from eBay, so it wasn't really going to be plug-n-play regardless. I just had to reposition the sensor so the trigger wheel would trigger it a bit earlier. Thus clocking the rotor to an earlier spot in its rotation.
 
As noted by JohnMc, I would worry less about the absolute value of the compression numbers than the variation between cylinders which is a big problem. Depending on whether you used an F or B head gasket, the actual duration of whatever camshaft you really have in the engine, what was done to the combustion chamber ..., these could all alter the test pressure during the compression test. You are is SoCal so I am going to assume close to sea level? If so, that eliminates the need to alter the test results to reflect compression test results which are typically always referenced to sea level.

The 20% variation between #1 and #4 is a huge problem. Did you have the combustion chamber volumes checked to make sure that they are uniform? Normally when you increase the swept volume of the engine (2130cc) and leave the combustion chamber volume untouched you end up with very high static compression ratios and should show a very high compression test result. If somebody changed the combustion chamber volumes to drop the static compression ratio to something reasonable they may have botched the combustion chamber reshaping creating your variance. If you have the combustion chamber volumes you should be able to calculate the static CR - if you know what head gasket you have. Was your block decked to level out the piston height and do you know what piston to combustion chamber clearance the engine is running?

Assuming the combustion chamber volumes were not screwed up and that something is not up with your rings, valves and valve gear would be the likely culprits. If you have access to a dial gauge and base, the first minimally invasive test that you could do would be to use the dial gauge to measure the actual valve lift on the valve retainer as you manually turn the engine over. If there is significant variation between the valves you have a problem with your rockers or your camshaft. The lifts on my B20E were all within +/- 1.5% of the average lift.

I had a 3 angle valve job done on my head and the machine shop bolexed it. I caught it because the valves would not seal while I was trying to CC my heads. I checked the fit of the valves in the seats using Prussian blue and they were a mess. Took the head to a competent shop and they cleaned up the seats. Apply Prussian blue to the valve seats, insert valve into seat, rotate a couple of times and remove. On a good valve job you should have a nice even band showing through the Prussian where the valve is contacting the seat. Any unevenness in that band and its back to the machine shop. I caught this before I installed my head. Unfortunately the only way to reliably check for a valve sealing problem without disassembly is to do the aforementioned leak down test.

I would leave the ignition and carb issues until later. Carburettor and ignition problems don't cause flakey compression readings. Address the compression problem first.
 
Since the cam is a knock off. That means it's probably a regrind. Which means it's ground on a smaller base circle which you are going to have to account for with lash caps.

I had a Isky vv71 in my 123gt and it ran great up to about 6500 or so. Wasn't happy trying to rev any higher than that. This was with dual springs as well.
 
I'll second the valves not being right issue. The shop that did a couple of 530's up here with bigger valves couldn't comprehend the need to either replace or cut the sets to accept the bigger valves. Vacuum was low and had 2" of flutter. Their QC/counter guy said they were fine, held a vacuum (while the pump was running). Poured water on the valve head and it instantly ran thru to the runner, he said that's water, not air. Took the head to another reputable shop who laughed at how bad it was, his jaw dropped when he heard the shop name that did it. Once done correct, the valves hold vacuum, water doesn't run thru, the flutter is gone, and the running issues are gone...go figure. lol
 
dl242gt said:
Since the cam is a knock off. That means it's probably a regrind. Which means it's ground on a smaller base circle which you are going to have to account for with lash caps.

I had a Isky vv71 in my 123gt and it ran great up to about 6500 or so. Wasn't happy trying to rev any higher than that. This was with dual springs as well.
Click to expand...

I recall, at the time that the numbers they gave me when they degreed the cam didn't align with the VV-71 numbers. This is what prompted me to go down to ISKY in person with the cam.

The numbers they gave me were:

207? @0.050
243? @0.010
443 Lift
298 Lobe
​

Those numbers didn't mean anything to me at the time (and they still don't because signature), and given the fact that ISKY themselves confirmed the VV-71 profile I didn't give it a second thought. Classic bone head move.
 
I'm not good even in the slightest at reading cam specs, but if that .050 duration is to be believed, looking at this set of cam specs: http://www.1800philes.com/ianr/_superlist_grinds.html

That would put yours waaay up in the 'tractor' end of the list. A little better than a B, a little worse than a C. I *think* the .010 lift would go along with that link's 'advertised duration' column, which is also at the same end of the list.

The A and B cams were what they put on the stock PV motors to make sure their cheapest car (the lightweight 544) didn't outrun their most expensive (the 2 - 3 hundred pounds heavier 1800S). And that dyno curve is about what my PV's original B18 motor felt like. Not much of a point in revving it - just go ahead and shift early. I swapped a D cam into it pretty early on and made it a LOT more fun to drive.

Sounds like maybe a new 'known' camshaft might be on your Christmas shopping list?

I have an Isky VV81 in mine, which is a pretty fun cam. Call it 3100-7500 rpms. And who knows, it might be the carbs (DCOE 40's - 36mm chokes) running out of puff at 7500 rpm. But I selected it more for its availability the last time I was replacing it. I was going to try something with a more modern lobe/spec, like a KG 19 ( http://www.kgtrimning.org/trimning-special/b18b20b30/kamaxlar/ ) but they were out and didn't expect to get any in stock for 3 - 6 months. And the Iskys are cheap, and ship immediately. So that's what I used.
 
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If those cam durations are correct, that just makes the problem with the compression tests that much worse. A 207 deg duration is significantly less than a Volvo D or K cam and you should be getting compression test values significantly higher than what you would get for a B20E engine - unless your static compression ratios are completely messed up. With a 2130 cc swept volume, that cam duration and unmodified combustion chamber volumes on a B or E head I would expect that your compression test values should be way above 150 psi.

In your first post, you listed the CR as 9.5:1. Where did that number come from? Was it calculated? With a 2130 cc swept volume the combustion chambers on a B or E head would need to be opened up to get the CR down to that value. My stock E head combustion chamber CCs out at about 45 cc and I am guessing that a B head should be around 50cc. Allowing a very generous 8cc for gasket and quench volume, a 2130 cc swept volume would give a static CR of 11 with an E head and about 10.2 with a B head. 'Correct' quench volumes would nudge those numbers higher. Did you drop the CR by putting a very fat head gasket in or were the combustion chambers reshaped?

I am guessing that the lift of 443 refers to a lift of 0.443" measured at the valve. Volvo D and K cams have 'advertised' lifts of 0.42" with a 1.5 rocker ratio. My brand new D cam had valve lifts that averaged out at 0.404" with freshly reprofiled rockers - Volvo rockers rarely matched the advertised value of 1.5. If you were running stock Volvo valve springs a lift of 0.443" could be bordering on static coil bind at full open and if not, might be running into dynamic bind at higher RPM. I believe that you have larger valves and double valve springs. Did you check for coil bind on the valve springs after the engine was assembled? This problem may be made worse if someone tried to grind your rocker arms to try and nudge up the rocker ratio.

Given the additional evidence, I am more convinced that this is not a tuning issue and that you have some mechanical
 
Yeah, I'd be troubleshooting that compression issue more before pulling the head and cam out.

Have another round of compression testing.
- pull all 4 plugs out so it cranks round and round with some decent cranking RPM
- hold the throttle open while testing
- test 'dry'
- put a small amount of oil in the cylinder (like a tablespoon), crank it around a couple of times, and then test it again

That 'wet' test can help rule out piston ring issues. It makes a temporary better compression seal if the rings are not sealing properly for a variety of reasons (worn out, stuck in their grooves, not bedded in properly, etc). If it jumps up - you need to pull the pistons and see what's going on. If it stays relatively the same, your compression issues lie elsewhere. Still could be the bottom end - things like compression height differences, cracked/holed pistons won't improve with a little oil.

If you can do even a basic shade tree leak down test it would be more informative. Just use an air hose and blow air into the cylinder at TDC (or at least with the valves closed), and then listen to where it's coming back out. If it's coming out of the block, it's something wrong with the piston (or possibly head gasket). If it's coming out of the intake - it's a valve, same with the exhaust. If it's coming out the coolant, it's the HG.

Then once you've gotten that tidbit of information, pull the head off. Eyeball the HG really well, see if there's any indication it was leaking. Maybe do a quick sanity check on the compression height - run the pistons to TDC and measure them vs. the block deck (flat edge and feeler gauges). I'd tend to think it would be a fairly large difference to produce a 30psi swing in compression, but just rule out that some mismatched parts got put in.

Another sort of leak down test that can be performed with the head off - pour a little light oil or even gasoline on top of a 'good' cylinder and to a similar depth in one of the 'suspect' cylinders - and then see how long it takes for that to leak past the rings and down into the oil pan. You can also do a similar shade tree leak test on the valves as well, set it upside down, pour some gas or light oil in the chambers, see if it stays there or leaks into an intake or exhaust port.

At this point, I tend to think the dyno graph is mostly the effects of a weird low-revving cam. But you may have uncovered a somewhat unrelated issue with the compression tests.
 
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A Cold compression test is a go or nogo test and it passed, it has over 90# so it will fire up.
Get it hot and properly broken in (if not already) and re test hot.
If it was not pushing out oil or showing a lot of blowby, I would not attribute the power loss to ring seal.

While its cold put a degree wheel on it and see where the cam is at, that is most likely where your problem is.
See where the intake valve closes Should be 30 - 50? ABDC, this is what determines the cranking compression #'s.
That will tell you instantly if there is a problem with the cam alignment.
You don't need to pull the head, just hair ball it. A cold lifter will not leak down much, and if you crank the motor a bit for oil pressure they will pump right up.
You are not trying to profile the cam just get an idea of where the intake is closing within 5 or 10? to see if it is a tooth off.
If you have solid lifters no worries, measure it.
If the lifters leak too much you can rotate the motor backwards and watch for movement on the intake and get it within a few degrees.
If it is a tooth off it will be 20? or more off, way early or way late.
If the intake is closing within that span you can look elsewhere for the problem.
To be missing that much power it will be something big.

Have you verified the TDC mark you are using for spark timing is good? Balancers slip, very common.
 
B18/B20's are all solid lifters. There's no oil supply at all on the lifter bores - it's all just oiled from oil dripping down from the rocker shaft.

And they have solid front pulleys too. Of course, they could be bolted on wrong.
 
My point is things have to be verified, maybe someone left the key out of the balancer.

Diagnosis is a logical progression verifying and eliminating factors.
Making any assumptions, it's likely the problem will be passed over.

Solid lifters makes it real easy and you can actually in a hairball fashion profile the cam without removing the head.
With Lobe centers plotted you can determine the separation angle, purty near ID the cam with that data.
 
Everything posted so far has been valid, but i will mention that I have seen wet compression increases from sources other than rings. Particularly poorly seating valves.
 
oemoilleaks said:
UPDATE:

I had an hour and was able to do a cold compression test. Results were not good, and I checked on two different gauges.

CYL 1 - 150psi
CYL 2 - 130psi
CYL 3 - 125psi
CYL 4 - 120psi

I also noticed that the VV-71 cam calls for a valve lash of 0.020, set while hot. I don't think I accounted for that lash, so when I get a minute I will warm up the engine, reset the lash, and re-test compression.
Click to expand...

Obviously those compression readings are too low. Even at 9.5:1 you should have at least 175psi.

The next step should be a leakdown test which will reveal what is leaking.

FYI, in my copy of the B20 green book, Volvo valve lash setting specs are the same whether the engine is hot or cold. This is because the involved components are either high quality cast iron or steel and they expand and contract at about the same rate.
 
JohnMc said:
Yeah, I'd be troubleshooting that compression issue more before pulling the head and cam out.

Have another round of compression testing.
- pull all 4 plugs out so it cranks round and round with some decent cranking RPM
- hold the throttle open while testing
- test 'dry'
- put a small amount of oil in the cylinder (like a tablespoon), crank it around a couple of times, and then test it again

That 'wet' test can help rule out piston ring issues. It makes a temporary better compression seal if the rings are not sealing properly for a variety of reasons (worn out, stuck in their grooves, not bedded in properly, etc). If it jumps up - you need to pull the pistons and see what's going on. If it stays relatively the same, your compression issues lie elsewhere. Still could be the bottom end - things like compression height differences, cracked/holed pistons won't improve with a little oil.

If you can do even a basic shade tree leak down test it would be more informative. Just use an air hose and blow air into the cylinder at TDC (or at least with the valves closed), and then listen to where it's coming back out. If it's coming out of the block, it's something wrong with the piston (or possibly head gasket). If it's coming out of the intake - it's a valve, same with the exhaust. If it's coming out the coolant, it's the HG.

Then once you've gotten that tidbit of information, pull the head off. Eyeball the HG really well, see if there's any indication it was leaking. Maybe do a quick sanity check on the compression height - run the pistons to TDC and measure them vs. the block deck (flat edge and feeler gauges). I'd tend to think it would be a fairly large difference to produce a 30psi swing in compression, but just rule out that some mismatched parts got put in.

Another sort of leak down test that can be performed with the head off - pour a little light oil or even gasoline on top of a 'good' cylinder and to a similar depth in one of the 'suspect' cylinders - and then see how long it takes for that to leak past the rings and down into the oil pan. You can also do a similar shade tree leak test on the valves as well, set it upside down, pour some gas or light oil in the chambers, see if it stays there or leaks into an intake or exhaust port.

At this point, I tend to think the dyno graph is mostly the effects of a weird low-revving cam. But you may have uncovered a somewhat unrelated issue with the compression tests.
Click to expand...

I need to do another compression test I think. And I want to reset the lash to .020 before I do it. I've had a busy week so I wasn't able to get anything done, but I will update the tread as soon as I can.
 
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