Ok... so may seem a stupid question... but here goes.
When I compress all the cylinders, I can hear air escaping somewhere. I just replaced with a new head gasket.
So, question; Do the exhaust and intake valves (when both closed at TDC) come to the same height?? Look at the pic and tell me I'm not crazy... but it looks like the exhaust valve is still slightly open when compared to the intake. This is the same on all four, hence the low compression on all four.
Thoughts??
Thanks fellas
edit: Sorry for the upsidedown picture... 8.gif
Rich
Depends.....
Has it had a valve job? did you have hardened seats installed?
Generally, the valves should be the same height, and while there could be a small difference, it shouldn't be large....so I would pull the head yet again and see if the exhaust valves are bent and/or sticking. Alternatively, you can set one cylinder to TDC and put air into the cylinder to hold the valves closed, then remove the spring and keeper, take the air pressure off momentarily and see if the valve moves freely. However, in trying to do this, if the valve is bent or being held open you may not get enough pressure to maintain the valve closed to get the keepers off....if that happens the head has to come off again anyway.
Bottom line, I would pull the head and see what's up. You definitely have a fundamental systemic problem with your compression.
too bad you're not closer, I would like to help you see what's going on. The other thing you could do is put a dial indicator on the #1 intake valve and see where the cam timing is - but something is def wrong here. Another simple way to check cam timing is to leave the push rods in the first and 4th cylinder, set it on TDC #1 and the two push rods on #4 should be in rock (as you rotate the crank back and forth over TDC the intake and exhaust should each move with very little movement of the crank), and the two on #1 all the way down and not moving.
Quote from: MiniDave on September 20, 2020, 12:20:25 PM
Another simple way to check cam timing is to leave the push rods in the first and 4th cylinder, set it on TDC #1 and the two push rods on #4 should be in rock (as you rotate the crank back and forth over TDC the intake and exhaust should each move with very little movement of the crank), and the two on #1 all the way down and not moving.
I can tell that this is happening as described just by rocking the crank with the head and rockers in place... in/ex on #1 hold still and in/ex #4 rocks as you suggest.
Head was done years ago, but then the engine sat for about 10+ years until now... (998+60) has larger valves, hardened seats. My gut is saying that there could be an issue with the guides or the face of the valves on the seats (corroded?)... guess the head comes off again!
Thanks.
Rich
Yep, I would....it could be the valves are sticking or like you said, something under them. If nothing else, lap them in again. But first just pull one and see what you can learn.
can you tell where the air is escaping for sure? take off the rockers and put compressed air in the cylinder and verify the leak. If the intake seats were just ground and hard seats put in the exhaust that could account for the difference you see. Dont pull the head until you confirm the leak once its off you can only guess unless it's obvious. If sitting for a while you will hear some air hissing past the rings just do the compressed air thing and listen to intake exhaust and crankcase.
If it's any help I started another thread with photos of a copper head gasket as removed from my 850 which had good seal.
http://www.restorationmini.com/forum/index.php?topic=2347.msg43949#msg43949 (http://www.restorationmini.com/forum/index.php?topic=2347.msg43949#msg43949)
Quote from: jeff10049 on September 20, 2020, 01:45:42 PM
can you tell where the air is escaping for sure? take off the rockers and put compressed air in the cylinder and verify the leak. If the intake seats were just ground and hard seats put in the exhaust that could account for the difference you see. Dont pull the head until you confirm the leak once its off you can only guess unless it's obvious. If sitting for a while you will hear some air hissing past the rings just do the compressed air thing and listen to intake exhaust and crankcase.
Ok.. so... put 90 psi to each cylinder (rockers off, all valves closed). I can hear through the crankcase breather from all cylinders. #2 cyl I can hear some air hissing in the exhaust.
Anything I can do to help the rings seal up after sitting for so long? Or am I just %$#??
I have had some luck un-sticking rings (if that is your problem) in other motors that have sat for a long time with a little Marvel Mystery Oil down each spark plug hole, let sit overnight then push outside before starting, start, once the smoke clears enough you can see, head for the highway for a little "Italian tune-up". A trip of 15-20 or so miles at varying speeds usually does the trick if it is going to work.
I am no expert on these little motors so this may not be a good idea on these, I am sure Dave and other real experts will chime in.
It goes without saying that an oil/filter change is in order, some do it before starting some after. You can run MMO in your oil so I have never worried about it harming anything for the few miles it's running before the filter change. Like I said though I am not sure if this is good advice on these motors with the single sump for the trans/motor I have only used this trick on old american V8 motors.
Can't hurt, but I doubt the MMO is what loosens the rings up, rather the Italian tune up is what does it.
However, if you're hearing air out the exhaust clearly that exhaust valve isn't seating properly. Marvel isn't likely to help that......but won't hurt the rest of the engine any if you decide to try it.
Now if it's just crud under the exhaust valve seat that's one thing, if it's not closing all the way due to sticking or being bent, running it hard will burn it for sure. I would still pull the head and remove all the springs and look at the seats. If the valves move freely in the guides, I would lap them in, put on some new stem seals (all 8 valves) then test them on the bench by putting the springs back on and pouring some gasoline into the port - if it doesn't leak you you're good to go - if it does, time to get the valves ground properly.
At that point you have a decision to make - pull the motor and rebuild it as needed - probably just a new set of rings, a light hone and some new rod bearing shells or bolt the head on and see what it does, knowing you're probably going to be pulling it anyway.
Do it right - do it once is always my philosophy.
Valves are out. Sorry forgot to take before and after pics.
Guides are great... valves are straight.
Is it normal for intake valves to have more carbon build up than exhaust??
Seats are ok... should lap in well... but none of these valves were really seating well...
Were there stem seals on the intakes? If not, I would put them on. If it's been running rich and burning oil then yes I've seen intakes carbon up badly - they run cooler than the exhaust valves so stuff can stick to them and not be burned off.
So, is the plan now to just lap them in and reinstall the head and then see what your compression is like?
So yeah, the stem seals on the intakes are in good shape.
And yes, it has always run on the rich side... so the junk on the intakes makes sense being cooler.
I think given that the valves cleaned up well... first couple have lapped in really well imo. I will likely bolt it all back together and see what the compression does. If after some use it doesn't come up it will go away for the winter and do a ring job in the spring if needed. As I said... it doesn't blow oil past the rings so I'm hoping that the bigger issue was the valves. Fingers crossed!
So far so good.. 17.gif .. all back together. Started first crank... warmed up nice, even a lap around the block. An improvement.
Retorque tomorrow and drive the piss out of it.
I don't want to make a career of lapping valves by hand... just saying.
Any improvements with compression?
I'll do a compression test once I see how it drives... first guess is that its come up... no more constant cranking to start it...
I chucked the hand lapper cup in my variable speed drill and made short work of lapping. Chucking the cup was kinda rube goldberg but worked. Later realized I could have just taken an old valve with double stick tape and chuck it in the vari drill back to back as in photo.
Was there evidence of poor seat contact? Should have been obviuos.
Quote from: Hercplt on September 27, 2020, 04:20:42 PM
I'll do a compression test once I see how it drivets... first guess is that its come up... no more constant cranking to start it...
Sounds familiar. I checked accel time and compared it to published spec.
Quote from: tsumini on September 27, 2020, 04:53:50 PM
I chucked the hand lapper cup in my variable speed drill and made short work of lapping. Chucking the cup was kinda rube goldberg but worked. Later realized I could have just taken an old valve with double stick tape and chuck it in the vari drill back to back as in photo.
Was there evidence of poor seat contact? Should have been obviuos.
Oh man... i was contemplating using a variable drill... but figured I should follow the rules... i didn't want to screw it up!! Next time...
And yes... they were very obviously not seating correctly. Intake valves were very crusty... and all the seats were rough looking... valves were ok... but not cleanly lapped if that makes sense. As I said... it was built about 20 years ago... and sat for the last 10+... God that makes me feel old!!
I was taught years ago as an apprentice that the valve needs to be lapped in and not to use a drill.
Now since then i have been known to use a drill when the pitting was bad and then lap in by hand.
Glad you have it sorted.
Quote from: Hercplt on September 27, 2020, 05:27:57 PM
Quote from: tsumini on September 27, 2020, 04:53:50 PM
I chucked the hand lapper cup in my variable speed drill and made short work of lapping. Chucking the cup was kinda rube goldberg but worked. Later realized I could have just taken an old valve with double stick tape and chuck it in the vari drill back to back as in photo.
Was there evidence of poor seat contact? Should have been obviuos.
Oh man... i was contemplating using a variable drill... but figured I should follow the rules... i didn't want to screw it up!! Next time...
And yes... they were very obviously not seating correctly. Intake valves were very crusty... and all the seats were rough looking... valves were ok... but not cleanly lapped if that makes sense. As I said... it was built about 20 years ago... and sat for the last 10+... God that makes me feel old!!
Yeah I tried the hand lap but that seemed more like making fire by rubbing two sticks together to make fire. I figgered
the worst that could happen was that I would have to take it down to a machine shop and have valves ground properly.
I found where the intake valves were obvously leaking and lapped them both. I lapped another but it had been sealing.
I didn't lap the other five since I had identified the leakers.
Photo shows the shiny sealing witness mark and dull leaky area with no witness mark.
Glad to hear it'a sorted.
Quote from: Jimini II on September 27, 2020, 05:40:32 PM
I was taught years ago as an apprentice that the valve needs to be lapped in and not to use a drill.
Now since then i have been known to use a drill when the pitting was bad and then lap in by hand.
Glad you have it sorted.
I would agree with that on an initial build but this is what we called a "field repair" best effort repair. It probably won't last as long as machine grind but buys a lot of time. Also probably wouldn't help burned valves either.
ok... final word on the compression issues...
I've run the Mini arouind (since re-lapped valves and bores well soaked with MMO) and still runs crappy... just mildly not as crappy as before.
Todays cold compression test as follows;
1. 110
2. 110
3. 113
4. 106
Same test after tablespoon of Marvel oil in the bores and some cranking...
1. 145
2. 145
3. 155 (#3 actually hit 210 and then I retested).
4. 135
Verdict? Gotta start shopping for new rings.
Yep, sounds like the rings got cooked somehow, time for a rebuild. Maybe take the opportunity to install some larger valves and do some port work, get it flowing a little better.
Was the head gasket sealing better than the first time you took the head off? or was there evidence of leaking (streaking) past the crimped lip? Loading up with oil in the CC should increase compression just as it would the rings.
Surely there's a better way to implicate the rings.
Quote from: tsumini on October 03, 2020, 06:29:02 PM
Was the head gasket sealing better than the first time you took the head off? or was there evidence of leaking (streaking) past the crimped lip? Loading up with oil in the CC should increase compression just as it would the rings.
Surely there's a better way to implicate the rings.
I think the leak down test done earlier also implcates the rings. An actual leak down tester to indicate the amount would be nice but the calibrated ear seemed to indicate rings on all cylinders. And valves on some.
You could pressure again and confirm valves are now good.
I'm pretty confident that its the rings at this point... I might put pressure on it again and see what I hear. With the valves re-lapped and an increase of only 10 psi indicates that the valves did their job and we removed a source of leak.
Head gasket that in installed looked great when I removed the head for the second time... the original was likely not torqued properly in the first place.
To answer another question above... the head was already ported, and large valves added... CC opened up and skimmed to get the CR up closer to 10:1.
I think opening it up to renew the rings and bearings... and a light honing should do the trick.
Thinking of replacing the VP7 with the SW5 cam while I have the chance. Should make a much nicer street 998, rather than the VP7 which (in the 998) is a bit lumpy and comes on too late.
Without knowing the specs on the VP7 vs the SW5 it's hard to say, but I've been using the Evo1 cam from Spares which is supposed to be about the same as the SW5 and it works well, plenty of torque down low.
10:1 should be seeing 180psi or so fyi.
Two things.
1. Re-read thread and saw that you reported the engine didn't smoke at all. Ring blowby and poorly installed rings leaking should smoke more the snoop dog.
2. Photo shows the relative height of exhaust/intake valves of a head I redid several years ago. The valves were eyeball level. You showed your head as being quite eyeball mismatched. I think was dismissed as being not usual but not a deal breaker. Today i stumbled on forum discussing a very similar problem except diesel and was 50 psi short on an expected 300 psi and exhibited the same running problems.
Someone suggested that valve seats were ground too deep and resulted in sinking the valves deeper into the head and expanding the combustion chamber volume and thus reducing compression ratio and compression itself. Wondering if your valves are too deep.
If it was mine I would measure the CC volume and establish actual CR and at least verify head is good. It may be worth it to avoid ring teardown. IMO lapping didn't do much and didn't prove head was good.
I'm kinda throwing this out cuz my gut tells me there is something wrong in your head. :-[ Excuse PUN
Tsumini;
I understand what you are saying regarding the valves coming in at different heights. Problem is that all the intake valves and all the exhaust valves match respectively. It was like this when first built and the thing was a rocket.
I will very likely have the head looked at in detail by someone more knowledgeable than me... and maybe re seat it..
When I put the whole story together (i.e. sitting for so long... hearing air pass into the crankcase, compression test results)... the logical conclusion is rings. Having said that, either way you look at it I am very likely going to have to open it up anyway and check for damage. I suppose that if there is none... then we can button up and go from there.
It is a good opportunity to set the motor up the way I have always wanted anyway... more torqy cooper style cam (SW5) rather than the faster road cam... that sort of thing.
Interesting stuff...
I've always wanted to know what this engine could do with the SW5...
Hercplt, No worries. Just trying to suggest a few things to look at to avoid going after the rings. I recall on mine that when compressed air was introduced I heard hissing in the sump from rings bypassing but could never determine if it was normal or excessive.
Good luck with your rebuild and hope to hear good results.
PS I re-read the thread and you did say it had run nlike a banshee at one point but i missed that.
Good luck again.
Quote from: tsumini on October 05, 2020, 03:18:28 PM
Hercplt, No worries. Just trying to suggest a few things to look at to avoid going after the rings. I recall on mine that when compressed air was introduced I heard hissing in the sump from rings bypassing but could never determine if it was normal or excessive.
Good luck with your rebuild and hope to hear good results.
PS I re-read the thread and you did say it had run nlike a banshee at one point but i missed that.
Good luck again.
Yes without an actual leak down tester its hard to guess whats normal because they always have some blow by. Then again I've had engines with 70% past the rings run very well. I also have a gut feeling the head could use a complete valve job and go through the rings and bores as well just give the whole thing a check out.