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Failure on Initial Engine Start After Rebuild
- Thread starter Gadwhite
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Re: trouble on 1st start
Dave,
Thanks for the nod about my "credo". I'm sure I can't add anything to the pile of advice you have been offered.....except perhaps, that by doing it all yourself it often makes troubleshooting less daunting. Even if it is valve timing you can go back and make sure it is correct because you've done it before but will probably pay more attention because you know you have a problem. I have gone to the emergency room several times from kicking myself in the butt so hard I thought I broke something. As I'm sure you already know, at some point the stuff you learn finding out what is NOT the problem will undoubedly serve you . My other credo on a different forum is " you live and you learn...if you're lucky!" . Keep us posted.
Dave,
Thanks for the nod about my "credo". I'm sure I can't add anything to the pile of advice you have been offered.....except perhaps, that by doing it all yourself it often makes troubleshooting less daunting. Even if it is valve timing you can go back and make sure it is correct because you've done it before but will probably pay more attention because you know you have a problem. I have gone to the emergency room several times from kicking myself in the butt so hard I thought I broke something. As I'm sure you already know, at some point the stuff you learn finding out what is NOT the problem will undoubedly serve you . My other credo on a different forum is " you live and you learn...if you're lucky!" . Keep us posted.
Healey Nut
Luke Skywalker
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Re: trouble on 1st start
You dont need a degree wheel to do the static valve timing . Do it like Randy shows in his earlier pics with a dial indicator .
pull off the rocker shaft and put the dial indicator probe in the cup of the pushrod and turn the engine by hand or by rocking it with it in gear .
Save all the messing around jacking engines and pulling parts off the crank .
You dont need a degree wheel to do the static valve timing . Do it like Randy shows in his earlier pics with a dial indicator .
pull off the rocker shaft and put the dial indicator probe in the cup of the pushrod and turn the engine by hand or by rocking it with it in gear .
Save all the messing around jacking engines and pulling parts off the crank .
red57
Jedi Knight
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Re: trouble on 1st start
I'm no pro but I like learning new tricks.
I'm not clear what it tells you in an assembled motor using dial indicators in the lifters if you don't have a degree wheel to know how many degrees before or after top dead/bottom dead center the valve is opening or closing.
I'm no pro but I like learning new tricks.
I'm not clear what it tells you in an assembled motor using dial indicators in the lifters if you don't have a degree wheel to know how many degrees before or after top dead/bottom dead center the valve is opening or closing.
All the cam cards I have tell you when the intake & exhaust open & close in degrees of crankshaft rotation. Which is what I would want to check. Love to learn a new way.
Dave
Dave
Re: trouble on 1st start
Mark. Agreed that’s my next step The Compresion is low . I did put oil in Cyl#1 but no change. Right now I am adjusting valves from scratch just in case I had them too tight,
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Re: trouble on 1st start
Gadwhite--
The fact that they are low and more or less consistent across the board makes me wonder. Perhaps your compression tester is not accurate. In any case I still think the car should start assuming good spark and proper cam timing. I hope you will keep us informed as to what the builder's response is to why the engine will not start.
Gadwhite--
The fact that they are low and more or less consistent across the board makes me wonder. Perhaps your compression tester is not accurate. In any case I still think the car should start assuming good spark and proper cam timing. I hope you will keep us informed as to what the builder's response is to why the engine will not start.
Bob Claffie
Jedi Knight
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Re: trouble on 1st start
Years ago a similar non starting problem with my son's MGB. Points grounded out inside the dizzy. Timing and fuel perfect, no spark.
Years ago a similar non starting problem with my son's MGB. Points grounded out inside the dizzy. Timing and fuel perfect, no spark.
Re: trouble on 1st start
Yes the builder did the short block, the heads were done separately, right now all indications are a valve or timing problem.I ruled out rings at this point. The compression is below the threshold to start
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Re: trouble on 1st start
Gadwhite, by the way, this thread has become somewhat epic now with over 100 posts and lots of good suggestions and discussion. You don't discourage easily, so congratulations on that.
I'm posting this just to mention that because there is so much good discussion on the thread that as Moderator I changed the name of the thread to make it more easily found in future searches on the subject. The first post subject - the subject that shows in the thread list - is now "Failure on Initial Engine Start After Rebuild." (All the rest of the posts in the thread still have the original title.)
I feel that the tiny amount of momentary confusion this might cause for some is outweighed by the longer-term benefit to those with similar problems searching the subject in the future. Thanks and sorry if you did a double-take looking for your original subject in the subject list!
Gadwhite, by the way, this thread has become somewhat epic now with over 100 posts and lots of good suggestions and discussion. You don't discourage easily, so congratulations on that.
I'm posting this just to mention that because there is so much good discussion on the thread that as Moderator I changed the name of the thread to make it more easily found in future searches on the subject. The first post subject - the subject that shows in the thread list - is now "Failure on Initial Engine Start After Rebuild." (All the rest of the posts in the thread still have the original title.)
I feel that the tiny amount of momentary confusion this might cause for some is outweighed by the longer-term benefit to those with similar problems searching the subject in the future. Thanks and sorry if you did a double-take looking for your original subject in the subject list!
Brinkerhoff
Jedi Knight
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Are you sure your exhaust system is clear and not plugged with a rag or a tomato?
Re: trouble on 1st start
Well that is progress .....
Here is my take on where we are. Correct me if I am wrong Gadwhite.
- Short block by builder
- Cylinder heads by another party/machine shop
- Assembled by Gadwhite?
- Compression check with throttles wide open is very low. (94,95,93, 90,90,90). Both dry and wet test on cylinder #1.
- "Exhaust for cylinders 1-3 has a large hole just after headers." which rules out down-exhaust blocking
- "Compression is below the threshold to start" (per builder?)
This short list rules out fuel and ignition, points to mechanical timing. Given that an engine is basically an air pump and that compression did not change significantly from the dry test to wet test, we are left with valve clearance or timing chain installation.
A previous reply said a recheck of valve clearance was going to be completed. Was clearance correct and we need another compression check?
On timing chain install a good pic can be found at HERE.
Onward!
Well that is progress .....
Here is my take on where we are. Correct me if I am wrong Gadwhite.- Short block by builder
- Cylinder heads by another party/machine shop
- Assembled by Gadwhite?
- Compression check with throttles wide open is very low. (94,95,93, 90,90,90). Both dry and wet test on cylinder #1.
- "Exhaust for cylinders 1-3 has a large hole just after headers." which rules out down-exhaust blocking
- "Compression is below the threshold to start" (per builder?)
This short list rules out fuel and ignition, points to mechanical timing. Given that an engine is basically an air pump and that compression did not change significantly from the dry test to wet test, we are left with valve clearance or timing chain installation.
A previous reply said a recheck of valve clearance was going to be completed. Was clearance correct and we need another compression check?
On timing chain install a good pic can be found at HERE.
Onward!
Jim 58 BN6
Jedi Trainee
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Re: trouble on 1st start
EDIT: After thinking about it, if you did adjust the valves or changed the cam timing, use the same compression gauge to see if the compression came up. If it's still too low, then compare its readings to those of another (hopefully known-to-be-good) gauge before tearing anything apart.
If you do another compression test, borrow another gauge just to rule out that the original one isn't somehow reading low (like it was dropped - ask me how I know).
This shouldn't be as difficult as it's been! Good Luck!
Well that is progress .....
- Short block by builder
- Cylinder heads by another party/machine shop
- Assembled by Gadwhite?
- Compression check with throttles wide open is very low. (94,95,93, 90,90,90). Both dry and wet test on cylinder #1.
- "Exhaust for cylinders 1-3 has a large hole just after headers." which rules out down-exhaust blocking
- "Compression is below the threshold to start" (per builder?)
This short list rules out fuel and ignition, points to mechanical timing. Given that an engine is basically an air pump and that compression did not change significantly from the dry test to wet test, we are left with valve clearance or timing chain installation.
A previous reply said a recheck of valve clearance was going to be completed. Was clearance correct and we need another compression check?
On timing chain install a good pic can be found at HERE.
Onward!
EDIT: After thinking about it, if you did adjust the valves or changed the cam timing, use the same compression gauge to see if the compression came up. If it's still too low, then compare its readings to those of another (hopefully known-to-be-good) gauge before tearing anything apart.
If you do another compression test, borrow another gauge just to rule out that the original one isn't somehow reading low (like it was dropped - ask me how I know).
This shouldn't be as difficult as it's been! Good Luck!
Last edited:
Bob_Spidell
Yoda
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re: "If you do another compression test, borrow another gauge just to rule out that the original one isn't somehow reading low (like it was dropped - ask me how I know)."
FWIW, the typical 'compression test' is only a rough estimate IMO anyway. Before we rebuilt my BJ8's engine, we tested--yep, throttles propped open--with three different, quality gauges. All were close--within 5% or so--but no two agreed exactly, nor are you likely to get exactly the same reading repeated with the same gauge (even using a charger or a second battery connected in parallel to keep starter speed consistent, just one of many variables). The superior method is a differential compression test, basically, a 'leakdown' test with gauges to measure the difference between an applied pressure and what the cylinder will maintain at TDC. For aircraft engines, usually 80psi is applied, and any maintained pressure below a certain amount is grounds for failure of the test (and potential grounding of the aircraft). For Lycoming engines, anything below 70psi was suspect, though Continentals were known for showing poor numbers--e.g. 50psi--but running smoothly.
Obviously, the engine in question's numbers are very poor, but I think you should get some combustion anyway (gasoline burns pretty well even at atmospheric pressure). The BJ8's #2 cylinder was effectively 'dead' at 60psi +/-, but it still fired and the engine ran reasonably smooth for tens of thousands of miles. I did note when using a pair of Colortunes--on #2 and #5--that the #2 didn't show 'bunsen blue,' or any other color while the #5 showed blue/orange.
FWIW, the typical 'compression test' is only a rough estimate IMO anyway. Before we rebuilt my BJ8's engine, we tested--yep, throttles propped open--with three different, quality gauges. All were close--within 5% or so--but no two agreed exactly, nor are you likely to get exactly the same reading repeated with the same gauge (even using a charger or a second battery connected in parallel to keep starter speed consistent, just one of many variables). The superior method is a differential compression test, basically, a 'leakdown' test with gauges to measure the difference between an applied pressure and what the cylinder will maintain at TDC. For aircraft engines, usually 80psi is applied, and any maintained pressure below a certain amount is grounds for failure of the test (and potential grounding of the aircraft). For Lycoming engines, anything below 70psi was suspect, though Continentals were known for showing poor numbers--e.g. 50psi--but running smoothly.
Obviously, the engine in question's numbers are very poor, but I think you should get some combustion anyway (gasoline burns pretty well even at atmospheric pressure). The BJ8's #2 cylinder was effectively 'dead' at 60psi +/-, but it still fired and the engine ran reasonably smooth for tens of thousands of miles. I did note when using a pair of Colortunes--on #2 and #5--that the #2 didn't show 'bunsen blue,' or any other color while the #5 showed blue/orange.
It’s interesting you should ask that. I did check that a couple of days ago. Bank 1 (cyl 1to 3) is disconnected after the headers and bank 2 I can feel air coming out exhaust.
I need to locate another gauge, I’ll re test during the week. After that I will pull the harmonic balancer off, remove timing chain cover and get a good picture of what’s going on there.
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Gadwhite--
As Bob suggests you might think about acquiring or borrowing a leak-down compression tester. Aside from being more accurate it allows you to test the compression of each cylinder when it is (theoretically) sealed up with both valves closed, both at bottom and top of piston travel, allowing you to point a more accurate finger at the source of compression leaks, etc. You will need a source of compressed air in order to use one--a small compressor/tank will work.
I hope you do not get in the situation where the guy who did your head and the guy who did your block start pointing fingers at each other--or you, for that matter.
As Bob suggests you might think about acquiring or borrowing a leak-down compression tester. Aside from being more accurate it allows you to test the compression of each cylinder when it is (theoretically) sealed up with both valves closed, both at bottom and top of piston travel, allowing you to point a more accurate finger at the source of compression leaks, etc. You will need a source of compressed air in order to use one--a small compressor/tank will work.
I hope you do not get in the situation where the guy who did your head and the guy who did your block start pointing fingers at each other--or you, for that matter.
Brinkerhoff
Jedi Knight
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With the valve lash set equal ( .015") then both the intake and exhaust valves should be open the same amount just BEFORE TDC on the intake stroke ( the intake starting to open and the exhaust almost closed ) . Find the spot where they are open the same amount ( lay a credit card on top of the valve retainers) then note the position of the crankshaft pulley marks ( assuming they accurately determine TDC). If the picture you supplied is at TDC then it looks like the intake valve hasn't started to open yet meaning the cam timing is late ( may just be off a tooth). Accurate cam timing begins with using a degree wheel to find exact TDC and verify its position with the factory marks but you can easily do this before you tear into the engine.