Spent a fair bit of time on this rebuild.
I decided to source a brand new block before the rebuild and acquired one from a third party. I had my head reconditioned and pressure tested prior to build.
Rebuild has been:
OEM gaskets
OEM Timing Chain Kit and sprockets
Mahle Forged Pistons (12.3:1)
Carrillo H Beam Rods
OEM crank
Piper Stage 3 Cams
Flat Face Valves
MWR Uprated Springs
MWR Titanium Retainers
MWR Uprated Oil Pump
OEM Water Pump
Fully ARP studded
Elise Parts Sump
Anyway. Long and short of it. did a bench test. #1, #2 and #4 are giving good compression (240, 250 and 250psi respectively) but #3.... getting 120psi.
Break my bad news what the problems might be, as I see no obvious reason. Every part is new and has been spec checked before install as per the part manual, or toyota spec sheet.
The only thing that I never checked, as it was new, was the block for cracks. Only a visual inspection.
Faulty piston maybe, or the rings not seated properly. Maybe get an impact gun on the crank bolt and give the engine a good turn over, and recheck. Might just need breaking in.
could be valves not seated properly. some grit under them or shims too big.
or head gasket leak.
I think you have to start taking it apart to to see.
Quote from: jonbill on April 19, 2021, 08:17could be valves not seated properly. some grit under them or shims too big.
or head gasket leak.
I think you have to statt taking it apart to to see.
A leakdown test could be done for this, without the need to start pulling it apart.
Sounds like a slight problem with a valve seating properly. I doubt it's rings or the head gasket (but it could be).
The idea of whizzing it over with an impact gun is not a bad one. If it's a bit of something in a valve seat, it might just blow through. You could also turn the engine by hand and open each valve in turn and blow through with compressed air. If it's a bit off something on a valve seat, it might blow it clear.
Did you check the valve seating before you installed the head, by any chance? I usually do it by pouring a little petrol into the combustion cavities and see if the valves hold it back. Can't do that with the head on the block, though, so that's not much help right now.
As jonbill suggested, a tight valve might be the issue, so double checking the valve clearances is a good place to start.
I can't see that a leakdown test will pin-point the issue, except to confirm the cylinder is not holding compression.
If the low compression persists, you'll have to pull the head.
At least it's on the engine stand, and not in the car!! I'm sure you'll get to the bottom of it quickly.
I'd do a leakdown test prior to stripping it down. It should point to where the air is going, gives you an indication at least.
Quote from: Carolyn on April 19, 2021, 08:57Sounds like a slight problem with a valve seating properly. I doubt it's rings or the head gasket (but it could be).
The idea of whizzing it over with an impact gun is not a bad one. If it's a bit of something in a valve seat, it might just blow through. You could also turn the engine by hand and open each valve in turn and blow through with compressed air. If it's a bit off something on a valve seat, it might blow it clear.
Did you check the valve seating before you installed the head, by any chance? I usually do it by pouring a little petrol into the combustion cavities and see if the valves hold it back. Can't do that with the head on the block, though, so that's not much help right now.
As jonbill suggested, a tight valve might be the issue, so double checking the valve clearances is a good place to start.
I can't see that a leakdown test will pin-point the issue, except to confirm the cylinder is not holding compression.
If the low compression persists, you'll have to pull the head.
At least it's on the engine stand, and not in the car!! I'm sure you'll get to the bottom of it quickly.
The whole point of a leakdown test is to pin pinpoint where the leak is coming from. As the engine is on a stand with no manifold or inlet attached it will clearly tell you if its a valve not seated correctly as you will be able to hear and feel air seeping out the port. You will also hear/feel It leak out the head gasket, or the block if thats the issue too.
Quote from: JB21 on April 19, 2021, 09:18Quote from: Carolyn on April 19, 2021, 08:57Sounds like a slight problem with a valve seating properly. I doubt it's rings or the head gasket (but it could be).
The idea of whizzing it over with an impact gun is not a bad one. If it's a bit of something in a valve seat, it might just blow through. You could also turn the engine by hand and open each valve in turn and blow through with compressed air. If it's a bit off something on a valve seat, it might blow it clear.
Did you check the valve seating before you installed the head, by any chance? I usually do it by pouring a little petrol into the combustion cavities and see if the valves hold it back. Can't do that with the head on the block, though, so that's not much help right now.
As jonbill suggested, a tight valve might be the issue, so double checking the valve clearances is a good place to start.
I can't see that a leakdown test will pin-point the issue, except to confirm the cylinder is not holding compression.
If the low compression persists, you'll have to pull the head.
At least it's on the engine stand, and not in the car!! I'm sure you'll get to the bottom of it quickly.
The whole point of a leakdown test is to pin pinpoint where the leak is coming from. As the engine is on a stand with no manifold or inlet attached it will clearly tell you if its a valve not seated correctly as you will be able to hear and feel air seeping out the port. You will also hear/feel It leak out the head gasket, or the block if thats the issue too.
I stand corrected.
To be clear, do you have a brand new, factory built OEM shortblock?
Quote from: Alex Knight on April 19, 2021, 10:28To be clear, do you have a brand new, factory built OEM shortblock?
No, a new bare block.
Quote from: Carolyn on April 19, 2021, 08:57Sounds like a slight problem with a valve seating properly. I doubt it's rings or the head gasket (but it could be).
The idea of whizzing it over with an impact gun is not a bad one. If it's a bit of something in a valve seat, it might just blow through. You could also turn the engine by hand and open each valve in turn and blow through with compressed air. If it's a bit off something on a valve seat, it might blow it clear.
Did you check the valve seating before you installed the head, by any chance? I usually do it by pouring a little petrol into the combustion cavities and see if the valves hold it back. Can't do that with the head on the block, though, so that's not much help right now.
As jonbill suggested, a tight valve might be the issue, so double checking the valve clearances is a good place to start.
I can't see that a leakdown test will pin-point the issue, except to confirm the cylinder is not holding compression.
If the low compression persists, you'll have to pull the head.
At least it's on the engine stand, and not in the car!! I'm sure you'll get to the bottom of it quickly.
I did do a liquid check of the head using petrol to confirm the valves were seating immediately prior to installation. However obviously this is a gravity check and no pressure involved, but was to ensure there was no grit, dust, metal, etc.
Valve clearances were all set to the loose end of spec.
From memory with the feeler gauge (across all 4)
Inlet 0.1mm feeler fits, 0.15mm does not
Exhaust 0.25mm feeler fits, 0.3mm does not.
Quote from: AJRFulton on April 19, 2021, 11:22Quote from: Alex Knight on April 19, 2021, 10:28To be clear, do you have a brand new, factory built OEM shortblock?
No, a new bare block.
Hmmm, ok. Could be head or block then.
Out of interest, was there any particular reason you didn't got for an OEM shortblock?
An old trick is to pour little oil in to the cylinder and let it stand for couple off minutes, pressure up rings, same valves
Quote from: Alex Knight on April 19, 2021, 18:46Quote from: AJRFulton on April 19, 2021, 11:22Quote from: Alex Knight on April 19, 2021, 10:28To be clear, do you have a brand new, factory built OEM shortblock?
No, a new bare block.
Hmmm, ok. Could be head or block then.
Out of interest, was there any particular reason you didn't got for an OEM shortblock?
No point just to disassemble and go fully forged.
This engines going to lead a hard life. I'll be happy getting 3000 miles out of it.
Well........
Did a leakdown test and confirmed #3 inlet was leaking.
Broke the engine apart again and.... bother me.... discovered the remains of a crushed spider in the valve seat, must have crawled in at some point whilst I was working on it.
All 4 cylinders now have great compression.
Thanks for sharing. It makes you appreciate the importance of clean rooms for assembly.
well this is it, they engine isn't left open longer than need be and the garage is spacious and tidy - however a spider managed to crawl in there.
Valve must have been slightly open and well...
So it would have blown clear with compressed air.
The spider could have got in through the port, and probably did.
Glad you found a simple fix, must of been a meaty spider to keep valve open!, they do say they breed them big your side of border :D
Quote from: Carolyn on April 24, 2021, 09:00So it would have blown clear with compressed air.
The spider could have got in through the port, and probably did.
I tried compressed air and brake cleaner first, but on breaking down it was only a tiny bit of crud on the seat that was stopping the valve closing properly.
It almost certainly would have burned off as soon as the engine was fired, but do you go to the hassle of installing an engine knowing this?
Quote from: AJRFulton on April 24, 2021, 10:05Quote from: Carolyn on April 24, 2021, 09:00So it would have blown clear with compressed air.
The spider could have got in through the port, and probably did.
I tried compressed air and brake cleaner first, but on breaking down it was only a tiny bit of crud on the seat that was stopping the valve closing properly.
It almost certainly would have burned off as soon as the engine was fired, but do you go to the hassle of installing an engine knowing this?
True.