Javascript Disabled Detected

You currently have javascript disabled. Several functions may not work. Please re-enable javascript to access full functionality.

Bent push rod, no compression

Started by _Briggs_ , Jun 14 2017 09:45 PM

Please log in to reply

17 replies to this topic

#1 _Briggs_

Guests

Posted 14 June 2017 - 09:45 PM

Hey guys,

i had some trouble with the car the other day and ended up running a compression test. dont recall the figures right now but basically cylinder 1 was way down on all the others which were very similar. Pulled the rocker cover off and found that the push rod had slipped out from under the rocker arm. the rocker arm (roller rockers) looks fine but the push rod is slightly bent. pulled the rocker assembly off the 1st cylinder and ran a compression test again with some oil in there, still no compression. a few questions as i remove the head:

1. if i need to replace the valve, does that mean replacing all valves? could be expensive!

2. are all valves considered equal, or are some better than others, some bigger, etc.

3. what else will need replacing?

4. what caused this???

in case it helps, the motor is a 308 with yella terra stage 3 heads (not sure what that means exactly), it has roller rockers, solid lifters and a cam (not sure which one), springs are yellow so maybe YT also but unsure. nothing known about anything else. everything appears clean and in good condition with the obvious exception.

thanks guys,

Paul

Back to top

#2 TerrA LX

Fulcrum Fixture

Members
14,241 posts

Location:Sid 'n' knee
Joined: 31-May 06

Posted 14 June 2017 - 09:53 PM

How could you compression test if the valves are closed?

I would be more concerned with whats bending your pushrods...

Back to top

#3 rodomo

To advertise here, call 13TORANA

Members
17,997 posts

Name:R - O - B Dammit!
Location:Way out west of Melbourne Awstraylya
Joined: 10-December 05

Posted 14 June 2017 - 10:08 PM

Hey guys,
pulled the rocker assembly off the 1st cylinder
thanks guys,
Paul

As Terry said, If the valves cant open and close there can be no compression.
A Worn cam lobe has the same effect.
Bent pushrod usually means rocker geometry incorrect.(Trust me, I know :fool: )

Back to top

#4 _Briggs_

Guests

Posted 15 June 2017 - 07:08 AM

I was under the impression that with the assembly off but springs still on that the valves should have sealed creating compression from the air in the chamber, wasn't deliberate as such, just had it off when a mate came over to help. how do i check/adjust rocker geometry?

Back to top

#5 TerrA LX

Fulcrum Fixture

Members
14,241 posts

Location:Sid 'n' knee
Joined: 31-May 06

Posted 15 June 2017 - 08:18 AM

If the valve can't open then there is no intake to create cylinder filling vacuum/compression.

Check geometry basics, look for anything touching (pushrods on bore, pushrod to rocker etc) and check for coil bind.
Paperclip is your minimum gauge to clearance.
Google for more in depth information.

Edited by TerrA LX, 15 June 2017 - 08:19 AM.

Back to top

#6 _Briggs_

Guests

Posted 15 June 2017 - 11:36 AM

maybe a stupid idea but if i just replace the pushrod and check the clearances, the issue could just have been the the intake valve wasn't opening? even if i bend another rod this is much cheaper than removing the whole head, etc.

Back to top

#7 orangeLJ

Yes, yes I do post alot!

Members
10,259 posts

Joined: 02-May 06

Posted 15 June 2017 - 12:21 PM

That theory would only work if the piston was at the bottom of the inlet stroke when you started.(at full capacity)

If it was already up, then you'd be reading vacuum rather than compression.

Id check witness marks for rocker geometry and then refit a push rod and perform a comp test rotating the engine by hand, see how it looks on that pot.

Are your pushrods the right length?

Back to top

#8 LC-GTR-1969

Shed tinkerer

Members
1,162 posts

Location:New South Wales
Car:Which one?
Joined: 09-March 14

View Garage

Posted 15 June 2017 - 04:23 PM

~~Solid or hydraulic cam?~~

Sorry- just re-read original post...

As per others have said- you cant test compression without a rod in place to open valve.

Rod could have bent for several reasons- how long have you had the car? have you ever checked the clearances yourself? Could be rocker geometry issue but could also be clearance issue or spring bind.

Edited by LC-GTR-1969, 15 June 2017 - 04:29 PM.

Back to top

#9 _LS1 Taxi_

Guests

Posted 15 June 2017 - 04:31 PM

Replace pushrod and wind it over with spark plugs out and check for rocker bind. If all appears kosher, check for compression.

Back to top

#10 _Briggs_

Guests

Posted 15 June 2017 - 04:53 PM

thanks guys, to answer a few questions and add my own:

have only done about 5 hours driving with this motor, bought off a guy who i believe to be genuine saying it had about 2k on the clock since a rebuild.

i haven't checked clearances before but wouldn't know where to begin... i'll google it tonight.

can i take the push rod out of another cylinder and use it to check for bind?

i should have some time Monday to take a look so keep the info coming,

thanks all

Back to top

#11 _Bomber Watson_

Guests

Posted 15 June 2017 - 08:35 PM

thanks guys, to answer a few questions and add my own:

have only done about 5 hours driving with this motor, bought off a guy who i believe to be genuine saying it had about 2k on the clock since a rebuild.

i haven't checked clearances before but wouldn't know where to begin... i'll google it tonight.

can i take the push rod out of another cylinder and use it to check for bind?

i should have some time Monday to take a look so keep the info coming,

thanks all

Yes you can take a pushrod out of a corresponding valve from another cylinder (so intake for intake) and check for binding.

Roll the engine around by hand and check that the valve spring does not bind (not sure if double valve springs, if so report back as there are a few more steps) but make sure you have as above a paperclips width between the coils at full lift.

Also check the rocker geometry, google this and pick the first image should give you an idea.

Pushrods bend for a few reasons:

1: the valve is touching something. The side of the bore, the piston, huge carbon deposits, impossible to guess.

2: the spring is binding or the collet is hitting the guide. Check these closely.

3: poor rocker geometry. As above.

This shit is frustrating, back when I was 17 I had an engine that kept bending pushrods. Only found out years and a couple of engines later once I finally got around to pulling the head off that particular engine that it was because the valves were hitting the side of the bore lol.

99% probability you will not have that particular problem was just a relevent story.

Cheers.

Edited by Bomber Watson, 15 June 2017 - 08:37 PM.

Back to top

#12 _big jack_

Guests

Posted 16 June 2017 - 05:10 PM

I had this problem years ago on a holden red it pulled the rocker post out so I drilled thru the head and valve post and fitted a cotter pin. then it broke the rocker arm replaced the rocker arm and then it broke around the head boss where I fitted the pin. Starting to get really pissed off now I had to remove the head to get all the head bosses machined down to the depth of the broken boss.

But before I removed the head I undid all the rockers and wound the motor over by hand to check the push rods heights and on the one that kept breaking I noticed the push rod sitting higher than the rest and so I took side plate off and removed the lifter. On closer inspection the lifter circlip had let go and had pressurised which caused all the drama if that makes sense.

Bit long winded I know but it is something to consider.

Cheers

Back to top

#13 _Agent 34_

Guests

Posted 16 June 2017 - 05:19 PM

great info here gents. It seemed straight forward but there is multiple issues that may cause this.

one thing for sure the push rods encountering resistance that is greater than it's vertical strength allows.

G

Back to top

#14 EunUCh

Lotsa Posts!

Members
2,761 posts

Location:not this planet
Car:japos
Joined: 23-November 06

Posted 16 June 2017 - 07:06 PM

probly not of much use , but for what its worth.

rocker_geometry.jpg 15.5K 6 downloads

Back to top

#15 jpxu1

Forum Fixture

Members
548 posts

Location:Melbourne VIC
Joined: 13-November 05

Posted 17 June 2017 - 09:37 PM

Back in the day (late 70's/early 80's) I used to regularly bend one of the push rods for #1 cylinder in my XU1 engine.First time it happened we were out on a run in the countryside, so pulled the rod out and straightened it with a hammer and put it back in. Got us home, and I replaced it. it happened again, so wasn't as stressed doing the same remedy. After that I used to carry a spare and still remember they were $1-12 at Holden (bought a few), which was the cheapest fix at the time. Maybe I should've just not revved it so hard.....

Eventually the problem was diagnosed as a worn guide hole through the head and a set of guide plates solved the problem.

Hope you solve your problem.

Cheers,

JPXU1 :spoton:

Back to top

#16 _Briggs_

Guests

Posted 19 June 2017 - 10:22 PM

hey guys, was keen to get started today and had all the tools out (first day off in months)... got a call from the childcare, both kids have gastro - awesome. should get some time in a couple of weeks, thanks heaps for all your replies, lots to consider. i'll start by replacing the rod and hand cranking to check geometry and bind, compression test again and following that (if not resolved) a visual head inspection to check the valves. if none of those are the culprit i might just sent to to someone who knows a bit more about what they're doing.

thanks again

Back to top

#17 _Briggs_

Guests

Posted 31 July 2017 - 11:29 AM

took a while but i got a few hours the other day and was able to move the rods from another cylinder across and hand crank it. it seems luck must be on my side as there was no bind and i got full compression! pretty happy about that (and also that i hadn't removed the heads yet). what i did notice is that there is a reasonable amount of compression still available in the spring as it goes through each cycle, i'm thinking that the rod popped out of its slot and was then forced down causing the bend. my question now is how to adjust this? i've looked up a few videos but they all seem to need to know what cam there is and the use of feeler gauges and i have no idea what i have. is there another method? i saw that paperclip width mentioned but does it need to be more accurate than that? and do i need to apply that to the inner or outer spring?

Back to top

#18 koalasprint

Forum Fan

Members
295 posts

Name:Steve
Location:Melbourne
Car:LX SS Hatch
Joined: 30-April 10

Posted 01 August 2017 - 08:02 AM

Hi Paul,

if you are sure that they are solid lifters then adjust the lash on each rocker to 0.026". Half a turn is about 0.20" on Yella Terra rockers. I would also research your rocker arms to see if push rod guide plates are required. if they are and you don't have them then that's your answer. Have a look here for some reading.

https://www.google.c...pqCH4pJdMvQzT_g

Regards, Steve.