4a. Won’t start after full rebuild. Any ideas what to check next pse?

[Steven Whitaker]

On 11/24/2023 at 8:32 AM, Rob Salisbury said:

And another thought is that with all the low rev churning on the starter motor any cam /follower lube applied to the rebuilt engine will have been wiped off leaving near metal to metal contact, at least pour some fresh oil down each pushrod tube to help. 

Thanks.  I’ve done that a few times.  Got 50 oil pressure within 5 secs so think that’s ok,

[Steven Whitaker]

On 11/23/2023 at 3:24 PM, Michel Higuet said:

Until now one problem is found, the HT coil  (1.5ohm for a 6 volt coil with ballast or 3 ohm for 12v.)  The plan of inlet manifold is not flat but there was no test to prove it give an impact... For the rest I wait until I will know the values of the vacuum in the manifold and compression in the cyl. Until now I presume their will not be ok. When will it tested with a good HT coil?

In Dutch "Meten is weten" give in English  "to mesure is to know".

Remeasured and have 3 ohm.  My meter needed a new battery! 

[Rob Salisbury]

3 minutes ago, Steven Whitaker said:

Thanks.  I’ve done that a few times.  Got 50 oil pressure within 5 secs so think that’s ok,

Hi Steven,                                                                                                                                                                                                                                                                                                     The important thing here is (assuming new cam and followers) that the cam/follower interface is only lubricated by oil splash from the spinning crank so it's irrespective of oil pressure, the suggestion for a new cam is that the engine is run at 2 to 2.5K revs for 20 minutes or so on first start-up to prevent galling and pick-up of the 2 surfaces, (Newman Cam's with their indestructible and expensive followers dispute this).                                                                                                                                            Cheers Rob  

[Steven Whitaker]

I measured compression and each cylinder has 50psi and holds at that.

[ianc]

When the battery is trying to turn the starter motor, its output will be reduced to 8 or 9 volts - and that reduced value will be what is being fed to the coil.

In such circumstances, it is worth temporarily connecting a separate battery just to supply the coil with 12 volts, thereby giving a greater kick to the plugs.  But don't leave this battery connected for too long as one can cook the coil if the engine is not being turned.  This supplementary battery does not need to be very beefy, as the current required of it is quite small.

Ian Cornish

[trchris]

Well 50psi compression is no good far to low the bores may have dried out or the engine was built dry no wonder there’s hardly any suck at the carburettors l would put oil down the bores and recheck compressions.

Chris

[trchris]

Remember

Induction,,Compression,Ignition,Exhaust if one is missing or poor a 4stroke engine won’t start 

Chris

[BlueTR3A-5EKT]

7 minutes ago, trchris said:

Well 50psi compression is no good far to low the bores may have dried out or the engine was built dry no wonder there’s hardly any suck at the carburettors l would put oil down the bores and recheck compressions.

Chris

Or the valve timing is way out

[twostrokekid]

10 minutes ago, trchris said:

Well 50psi compression is no good far to low the bores may have dried out or the engine was built dry no wonder there’s hardly any suck at the carburettors l would put oil down the bores and recheck compressions.

Chris

My compression test with a standard engine, plugs out and throttle fully open 185 - 190psi cranking on starter.

[Steven Whitaker]

55 minutes ago, trchris said:

Well 50psi compression is no good far to low the bores may have dried out or the engine was built dry no wonder there’s hardly any suck at the carburettors l would put oil down the bores and recheck compressions.

Chris

Hi Chris.  Thanks for your response.  When I built the engine I oiled the whole thing.  I’ll try some oil down the bores, but how about valve timing.  My checks I think prove it’s ok but I begin to doubt…. Also, if I remove the rocker assembly and check for compression again, would that prove valve timing is out if I get higher compression?

[Steven Whitaker]

46 minutes ago, twostrokekid said:

My compression test with a standard engine, plugs out and throttle fully open 185 - 190psi cranking on starter.

Wow!  I have a problem then!

[Lebro]

Mine, after rebuild, & some tweaking ! is 200 PSI.

50 is way too low

Bob

[Steven Whitaker]

50 minutes ago, BlueTR3A-5EKT said:

Or the valve timing is way out

I’m beginning to question this, but I thought all I have checked ruled this out, but perhaps I need to pull the timing cover off and do it again?

Can I take rocker assembly off and turn the engine over to see if I get better comp?  Remove push rods for this?

[trchris]

Steve

The easiest way to check valve timing is rocking valves on number 4  with cylinder number 1  at TDC then check distributor is firing at number 1 if not then you’ll have to remove timing chain cover and check/ adjust once you’ve ruled this out then recheck compressions after putting oil in the bores

Chris

[Lebro]

Worth a try, one cylinder only. be very carefull if you pull any pushrods out, you can often pull the cam follower out of it's hole at the same time.

Twist the rod as you pull it slightly up, and you should feel the follower drop down, it's then safe to remove.

Bob

[Steven Whitaker]

34 minutes ago, Lebro said:

Mine, after rebuild, & some tweaking ! is 200 PSI.

50 is way too low

Bob

Ok thanks.  Where do you suggest I go next please?

[Lebro]

1 minute ago, trchris said:

Steve

The easiest way to check valve timing is rocking valves on number 4  with cylinder number 1  at TDC then check distributor is firing at number 1 if not then you’ll have to remove timing chain cover and check/ adjust once you’ve ruled this out then recheck compressions after putting oil in the bores

Chris

Sorry, but that just check ignition timing. Valve timing is a bit more complicated.

Bob

[Steven Whitaker]

3 minutes ago, trchris said:

Steve

The easiest way to check valve timing is rocking valves on number 4  with cylinder number 1  at TDC then check distributor is firing at number 1 if not then you’ll have to remove timing chain cover and check/ adjust once you’ve ruled this out then recheck compressions after putting oil in the bores

Chris

Ok, thanks Chris.

[BlueTR3A-5EKT]

12 minutes ago, Steven Whitaker said:

I’m beginning to question this, but I thought all I have checked ruled this out, but perhaps I need to pull the timing cover off and do it again?

Can I take rocker assembly off and turn the engine over to see if I get better comp?  Remove push rods for this?

Having just looked through this post at no point do you say how you checked the crank and pistons are at top dead centre TDC.

The fact the valves are rocking or have no lift is immaterial if the pistons are half way up the bores.   The timing of the cam to the crank is the critical thing. That is done by getting the crank at TDC and fitting the cam timing chain and sprocket once the cam is correctly orientated with valves on “the rock.”  If using standard cam.

Did you mark the new crank pulley once it was assembled with the crank at TDC and mark mot to match the pointer on the timing cover?    You must not take the pulley off its hub once you have done 5at as there are 6 different bolt holes meaning 5 places to assemble it wrongly.

Can you turn the engine by hand with the plugs out?    If so yo can check the TDC with a piston stop screwed in to the plug hole.

With the stop screwed in.   BY HAND turn crank carefully and gently until the stop is felt. ( no1 piston crown is touching the stop)   Mark the periphery of the crank pulley next to the timing pointer.    Now turn the engine by hand in the opposite direction until the stop is felt.    Mark the pulley again.   Half the  distance between the two marks on the pulley is TDC.

Alternatively this sort of sliding gauge would give a good idea of where the piston/crank are.

https://www.feked.com/tdc-timing-tool.html

 

Remove stop once you have confirmed and marked the TDC position.   

[Steven Whitaker]

Just now, Steven Whitaker said:

Ok, thanks Chris.

How should valves on cylinder 4 be when cyl 1 is at tdc please?

[Steven Whitaker]

3 minutes ago, BlueTR3A-5EKT said:

Having just looked through this post at no point do you say how you checked the crank and pistons are at top dead centre TDC.

The fact the valves are rocking or have no lift is immaterial if the pistons are half way up the bores.   The timing of the cam to the crank is the critical thing. That is done by getting the crank at TDC and fitting the cam timing chain and sprocket once the cam is correctly orientated with valves on “the rock.”  If using standard cam.

Did you mark the new crank pulley once it was assembled with the crank at TDC and mark mot to match the pointer on the timing cover?    You must not take the pulley off its hub once you have done 5at as there are 6 different bolt holes meaning 5 places to assemble it wrongly.

Can you turn the engine by hand with the plugs out?    If so yo can check the TDC with a piston stop screwed in to the plug hole.

With the stop screwed in.   BY HAND turn crank carefully and gently until the stop is felt. ( no1 piston crown is touching the stop)   Mark the periphery of the crank pulley next to the timing pointer.    Now turn the engine by hand in the opposite direction until the stop is felt.    Mark the pulley again.   Half the  distance between the two marks on the pulley is TDC.

Alternatively this sort of sliding gauge would give a good idea of where the piston/crank are.

https://www.feked.com/tdc-timing-tool.html

 

Remove stop once you have confirmed and marked the TDC position.   

Hi Pete.  I did the setting of the cam to crank when I rebuilt the engine with the head off.  The piston 1 was at tdc and I got the cam in the dwell position and carefully slid the cam gear on to line up with the screw holes in the cam.  
 

Since then during the current fiasco, I’ve removed a plug and can see top of the piston coming up, going down and if called tdc mid point and that coincides with both valves on cylinder 1 being closed.  This is why I think the valve timing is correct.

I used new timings sprockets and new chain and tensioner.  I’m using a new crank belt pulley as I’ve got the alternator.  i didn’t mark tdc on the crank pulley at the time…..

[Steven Whitaker]

9 minutes ago, BlueTR3A-5EKT said:

Having just looked through this post at no point do you say how you checked the crank and pistons are at top dead centre TDC.

The fact the valves are rocking or have no lift is immaterial if the pistons are half way up the bores.   The timing of the cam to the crank is the critical thing. That is done by getting the crank at TDC and fitting the cam timing chain and sprocket once the cam is correctly orientated with valves on “the rock.”  If using standard cam.

Did you mark the new crank pulley once it was assembled with the crank at TDC and mark mot to match the pointer on the timing cover?    You must not take the pulley off its hub once you have done 5at as there are 6 different bolt holes meaning 5 places to assemble it wrongly.

Can you turn the engine by hand with the plugs out?    If so yo can check the TDC with a piston stop screwed in to the plug hole.

With the stop screwed in.   BY HAND turn crank carefully and gently until the stop is felt. ( no1 piston crown is touching the stop)   Mark the periphery of the crank pulley next to the timing pointer.    Now turn the engine by hand in the opposite direction until the stop is felt.    Mark the pulley again.   Half the  distance between the two marks on the pulley is TDC.

Alternatively this sort of sliding gauge would give a good idea of where the piston/crank are.

https://www.feked.com/tdc-timing-tool.html

 

Remove stop once you have confirmed and marked the TDC position.   

I don’t have one of those timing tools but i think I’ll get one.  I’ll see if i can turn the engine by hand but i normally put her in 4th and rock it gently which i think i can get it to tdc pretty well.

[trchris]

Steve

With number 1 at TDC both valves on number 4 should be rocking ie one just closing the other just opening

Chris

[BlueTR3A-5EKT]

2 minutes ago, Steven Whitaker said:

Hi Pete.  I did the setting of the cam to crank when I rebuilt the engine with the head off.  The piston 1 was at tdc and I got the cam in the dwell position and carefully slid the cam gear on to line up with the screw holes in the cam.  
 

Since then during the current fiasco, I’ve removed a plug and can see top of the piston coming up, going down and if called tdc mid point and that coincides with both valves on cylinder 1 being closed.  This is why I think the valve timing is correct.

I used new timings sprockets and new chain and tensioner.  I’m using a new crank belt pulley as I’ve got the alternator.  i didn’t mark tdc on the crank pulley at the time…..

It would be a worthwhile thing to mark TDC on that new pulley.   You will then have a reference datum for timing the ignition.

[trchris]

Agree with Peter above mark the bottom pulley for TDC

Chris