Amazon: - Bent Push Rod

ColoradoAmazon · May 29th, 2024, 15:55

I purchased a 1962 121 that came with a rebuilt B18 engine. The previous owner installed the engine but never completed the installation or ever fired the engine.

I have completed the installation and have run the engine. The engine initially ran fine but started running rough. I discovered cylinder #1 had no spark and was really low on compression. I removed the valve cover and discovered the intake push rod on cylinder #1 was bend and is stuck in the head.

I'm a novice when it comes to engines so I'm looking for some input.

1 - How does something like this happen? (wondering if the valves were not adjusted properly. Some of the other push rods are loose)?
2 - I'm thinking I need to remove the rocker shaft, pull out the bent push rod, install a new push rod and adjust the valves.

Any input on what caused this and how to remedy would be greatly appreciated. Thank You!

Juular · May 29th, 2024, 16:25

Fairly certain this was caused by the clearance adjustment being in completely the wrong postcode. Too loose and the pushrod will jump out of the rocker assembly and possibly bend on the next cycle. Too tight and the forces in the valve train could bend it.

Nothing to lose by replacing that pushrod, maybe all of them (check for staightness) and redoing the clearances.

Rustinmotion · May 29th, 2024, 16:29

Bent pushrod could be a stuck valve or interference with valve and piston , binding springs or a sticking rocker arm, was the engine tuned? High lift cam or skimmed head?

ColoradoAmazon · May 29th, 2024, 18:09

I did not adjust the valves and just assumed they were adjusted properly. Definitely a mistake. I do not think they are adjusted correctly. Hopefully nothing other than the push rod/rods are damaged.

This is what information I have on the engine rebuild: "Rebuilt B18 bored out to a B20, B20 head shaved 2mm with a K cam". However I cannot confirm if any of this is true. I'm going by what's on an order form for some Mikuni carburetors and the previous owner's recollection. The engine builder passed away.

I'm going to remove the push rods and check them for straightness, buy some replacement push rods, replace the push rods, adjust the valves and check everything.

Off to watch some YouTube videos. Anything I should look out for?

Rustinmotion · May 29th, 2024, 18:22

Quote:

Originally Posted by ColoradoAmazon

I purchased a 1962 121 that came with a rebuilt B18 engine. The previous owner installed the engine but never completed the installation or ever fired the engine.

I have completed the installation and have run the engine. The engine initially ran fine but started running rough. I discovered cylinder #1 had no spark and was really low on compression. I removed the valve cover and discovered the intake push rod on cylinder #1 was bend and is stuck in the head.

I'm a novice when it comes to engines so I'm looking for some input.

1 - How does something like this happen? (wondering if the valves were not adjusted properly. Some of the other push rods are loose)?
2 - I'm thinking I need to remove the rocker shaft, pull out the bent push rod, install a new push rod and adjust the valves.

Any input on what caused this and how to remedy would be greatly appreciated. Thank You!

Quote:

Originally Posted by ColoradoAmazon

I did not adjust the valves and just assumed they were adjusted properly. Definitely a mistake. I do not think they are adjusted correctly. Hopefully nothing other than the push rod/rods are damaged.

This is what information I have on the engine rebuild: "Rebuilt B18 bored out to a B20, B20 head shaved 2mm with a K cam". However I cannot confirm if any of this is true. I'm going by what's on an order form for some Mikuni carburetors and the previous owner's recollection. The engine builder passed away.

I'm going to remove the push rods and check them for straightness, buy some replacement push rods, replace the push rods, adjust the valves and check everything.

Off to watch some YouTube videos. Anything I should look out for?

Check for spring binding, if the PO used updated valve springs without machining the spring pockets you could be binding up the springs once it’s back together hand rotate the engine and make sure at full open there is still a gap between each of the spring coils

Derek UK · May 30th, 2024, 10:59

Not the first time there has been a bent pushrod like this and it won't be the last. Roll pushrods on a sheet of glass. A mirror works fine. This may be the only one that needs replacing.
Be aware that some B18 blocks don't take to be being bored to B20 size due to core shifts when they were made. Can make the bore walls very thin and prone to cracking. If a good engine builder is aware of this the block can be checked before and after the rebore. Good luck.
Not sure what CR is now with a 2mm skim but best to user the highest octane gas you can.

Ron Kwas · May 31st, 2024, 12:12

CA;

The engine will likely have survived this issue if it happened on initial startup, and if corrected immediately, but you may consider engaging the help and oversight of an experienced "Engine Elmer"...because this sounds like a fundamental error to me, which an experienced guy would have avoided...

To add to info from others...(...been traveling so just catching up)...the significant forces necessary to bend a Pushrod can only be generated when something in the Valvetrain is not completely free to move as it should...and for a brand new (what I would consider to be a significantly modified engine), turning the Crankshaft manually through a few turns during valve adjustment, and BEFORE initial Startup to assure this, would have shown a stacked and binding Valvespring, or stuck Valve.

It sounds like the Valvetrain was anything but correctly adjusted "Some of the other push rods are loose"...the Valvetrain MUST be correctly adjusted before even thinking of starting!!! NO PRESUMPTIONS!

I'd advise you do some manual crankshaft rotations after replacing the bent Pushrod...paying particular attention to the Valvetrain including Valve clearance and adjustment on every single one at TDC for every single piston, NO EXCEPTIONS!)...all eight are essentially similar in action and clearance, so the situation that happened to one, might be in place on others...! Triple check everything and assure it is right, before attempting another startup!

Good Hunting!

ColoradoAmazon · May 31st, 2024, 18:10

Derek and Ron thank you for the input.

I checked the other push rods and they all seem straight. It was definitely a mistake not checking the valve adjustment. Hopefully not a catastrophic mistake.

I will definitely triple check everything this time around. It looks like Nordicar has a pretty good YouTube video I'll be following.

142 Guy · May 31st, 2024, 21:58

My initial reaction was, that in addition to the lack of clearance it is possible that you might have had a gross valve timing error (timing gears not timed properly). However, the fact that it initially 'ran fine' pretty much eliminates that as a possibility. Also, even with a gross timing error I think a B18/B20 with a K cam is a non interference engine so even a gross timing error would not cause a bent valve; however, skimming 2 mm might have changed that.

A lack of valve clearance might have caused the bent push rod; but, not a significant bend. The spec valve clearance for a K cam is 0.016". On my car with a D cam (same lift as K cam), my recollection is that the stock valve springs are not approaching coil bind at full valve opening. As such, even if the clearance were completely zeroed out I would not expect a bent pushrod which requires coil bind, or at best a very tiny bend in the pushrod. If the clearance had been zeroed out and then the adjuster tightened even further it might have been possible to approach coil bind which could bend the pushrod; but, I would expect the bend to be small.

However, I am thinking that based upon your description of events that perhaps it is more likely that the clearance was really excessive and as Juular identified, the pushrod popped out of place and got caught between the head casting and the rocker. Examining the pushrod for marks indicating mechanical contact might give you an idea as to whether this occurred. If this did occur, I would be inclined to carefully examine the rocker associated with the bent pushrod. You need to check it for damage / bending. Unfortunately, I am not aware of any measurement specs for 'out of true' so you will have to do this by checking a matching rocker(s) off of one of the other valve positions. Doing this reliably pretty much requires removing the rocker stand and disassembling it to get a couple of rockers so that you can do a side by side comparison with the rocker associated with the bent push rod. If you are unlucky and the rocker is bent I think you are pretty much into replacement. New rockers are not available; but, there are at least one or two vendors who have accumulated rockers from salvage engines.

I would also be inclined to check the valve for bending. To do this requires removal of the spring. With the correct know-how R&R of the spring can be done without removing the head; but, does require some effort in getting the spring back on.

The preceding is predicated on the basis of stock valve springs. With a K cam I would not expect dual valve springs; however, you should check (easy to do by inspection). If dual valve springs were installed then you would need to examine the seats to confirm that they were relieved to establish a correct installed spring length. However, if the valve seats were nor relieved then I would expect that you might have issues on all the valves so this seems unlikely. However, visual confirmation that dual springs have not been installed is easy to do.

ColoradoAmazon · Jun 4th, 2024, 15:14

142 Guy: Thank you for the input. I do agree that too much clearance might be to blame. I will inspect the rocker.

I received the new push rod from VP Autoparts. The new push rod is a little different compared to the old. This push rod appears to be a 2 or 3 piece design instead of a single piece. The shaft portion is a little bigger diameter. However the length, the ball at the bottom and the cup at the top appear to be very similar. Any issues running one slightly different push rod?

Should I be concerned about the split in the shaft near the top cup?

May 29th, 2024, 16:25	#2
Juular Senior Member Last Online: Today 10:46 Join Date: Sep 2020 Location: Falkirk	Fairly certain this was caused by the clearance adjustment being in completely the wrong postcode. Too loose and the pushrod will jump out of the rocker assembly and possibly bend on the next cycle. Too tight and the forces in the valve train could bend it. Nothing to lose by replacing that pushrod, maybe all of them (check for staightness) and redoing the clearances.

May 29th, 2024, 16:29	#3
Rustinmotion Senior Member Last Online: Today 21:07 Join Date: Sep 2021 Location: MILTON KEYNES	Bent pushrod could be a stuck valve or interference with valve and piston , binding springs or a sticking rocker arm, was the engine tuned? High lift cam or skimmed head?

May 29th, 2024, 18:09	#4
ColoradoAmazon Junior Member Last Online: Jul 26th, 2024 19:05 Join Date: Mar 2022 Location: Colorado	I did not adjust the valves and just assumed they were adjusted properly. Definitely a mistake. I do not think they are adjusted correctly. Hopefully nothing other than the push rod/rods are damaged. This is what information I have on the engine rebuild: "Rebuilt B18 bored out to a B20, B20 head shaved 2mm with a K cam". However I cannot confirm if any of this is true. I'm going by what's on an order form for some Mikuni carburetors and the previous owner's recollection. The engine builder passed away. I'm going to remove the push rods and check them for straightness, buy some replacement push rods, replace the push rods, adjust the valves and check everything. Off to watch some YouTube videos. Anything I should look out for?

May 30th, 2024, 10:59	#6
Derek UK VOC Member Last Online: Jul 25th, 2024 12:01 Join Date: Jul 2006 Location: Chatham	Not the first time there has been a bent pushrod like this and it won't be the last. Roll pushrods on a sheet of glass. A mirror works fine. This may be the only one that needs replacing. Be aware that some B18 blocks don't take to be being bored to B20 size due to core shifts when they were made. Can make the bore walls very thin and prone to cracking. If a good engine builder is aware of this the block can be checked before and after the rebore. Good luck. Not sure what CR is now with a 2mm skim but best to user the highest octane gas you can.

May 31st, 2024, 12:12	#7
Ron Kwas Premier Member Last Online: Today 17:14 Join Date: Jul 2007 Location: Connecticut, USA	CA; The engine will likely have survived this issue if it happened on initial startup, and if corrected immediately, but you may consider engaging the help and oversight of an experienced "Engine Elmer"...because this sounds like a fundamental error to me, which an experienced guy would have avoided... To add to info from others...(...been traveling so just catching up)...the significant forces necessary to bend a Pushrod can only be generated when something in the Valvetrain is not completely free to move as it should...and for a brand new (what I would consider to be a significantly modified engine), turning the Crankshaft manually through a few turns during valve adjustment, and BEFORE initial Startup to assure this, would have shown a stacked and binding Valvespring, or stuck Valve. It sounds like the Valvetrain was anything but correctly adjusted "Some of the other push rods are loose"...the Valvetrain MUST be correctly adjusted before even thinking of starting!!! NO PRESUMPTIONS! I'd advise you do some manual crankshaft rotations after replacing the bent Pushrod...paying particular attention to the Valvetrain including Valve clearance and adjustment on every single one at TDC for every single piston, NO EXCEPTIONS!)...all eight are essentially similar in action and clearance, so the situation that happened to one, might be in place on others...! Triple check everything and assure it is right, before attempting another startup! Good Hunting!

May 31st, 2024, 18:10	#8
ColoradoAmazon Junior Member Last Online: Jul 26th, 2024 19:05 Join Date: Mar 2022 Location: Colorado	Derek and Ron thank you for the input. I checked the other push rods and they all seem straight. It was definitely a mistake not checking the valve adjustment. Hopefully not a catastrophic mistake. I will definitely triple check everything this time around. It looks like Nordicar has a pretty good YouTube video I'll be following.

May 31st, 2024, 21:58	#9
142 Guy Master Member Last Online: Yesterday 22:50 Join Date: Jul 2020 Location: Saskatchewan, Canada	My initial reaction was, that in addition to the lack of clearance it is possible that you might have had a gross valve timing error (timing gears not timed properly). However, the fact that it initially 'ran fine' pretty much eliminates that as a possibility. Also, even with a gross timing error I think a B18/B20 with a K cam is a non interference engine so even a gross timing error would not cause a bent valve; however, skimming 2 mm might have changed that. A lack of valve clearance might have caused the bent push rod; but, not a significant bend. The spec valve clearance for a K cam is 0.016". On my car with a D cam (same lift as K cam), my recollection is that the stock valve springs are not approaching coil bind at full valve opening. As such, even if the clearance were completely zeroed out I would not expect a bent pushrod which requires coil bind, or at best a very tiny bend in the pushrod. If the clearance had been zeroed out and then the adjuster tightened even further it might have been possible to approach coil bind which could bend the pushrod; but, I would expect the bend to be small. However, I am thinking that based upon your description of events that perhaps it is more likely that the clearance was really excessive and as Juular identified, the pushrod popped out of place and got caught between the head casting and the rocker. Examining the pushrod for marks indicating mechanical contact might give you an idea as to whether this occurred. If this did occur, I would be inclined to carefully examine the rocker associated with the bent pushrod. You need to check it for damage / bending. Unfortunately, I am not aware of any measurement specs for 'out of true' so you will have to do this by checking a matching rocker(s) off of one of the other valve positions. Doing this reliably pretty much requires removing the rocker stand and disassembling it to get a couple of rockers so that you can do a side by side comparison with the rocker associated with the bent push rod. If you are unlucky and the rocker is bent I think you are pretty much into replacement. New rockers are not available; but, there are at least one or two vendors who have accumulated rockers from salvage engines. I would also be inclined to check the valve for bending. To do this requires removal of the spring. With the correct know-how R&R of the spring can be done without removing the head; but, does require some effort in getting the spring back on. The preceding is predicated on the basis of stock valve springs. With a K cam I would not expect dual valve springs; however, you should check (easy to do by inspection). If dual valve springs were installed then you would need to examine the seats to confirm that they were relieved to establish a correct installed spring length. However, if the valve seats were nor relieved then I would expect that you might have issues on all the valves so this seems unlikely. However, visual confirmation that dual springs have not been installed is easy to do.

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