Vt not starting after rocker install (backfires)

[2O4TS]

Double post

 

[2O4TS]

I have to ask a question. It may be obvious but it's a mistake i made years ago with one of my first engine builds.

I have done this exact job you're doing with the 1.98 rocker arms and Comp Cams pushrods with no issue myself.

My question is, when you torqued the rocker arms did you crank the engine through the cycle so that each piston was at TDC with the exhaust valve rocking as you torqued it?

If not, that is your issue. Somebody touched on it earlier but what will happen is that because your cam lobes are at varying positions you need to rotate the crankshaft in to position to torque the rocker arms on the side of the cam opposite the lobes otherwise if either of your cam lobes are starting to point up towards the valvetrain then you're preloading the rocker arms, the valves wont all close and/or open properly and you risk valvetrain damage and more depending on other modifications. You must make sure that each piston is at TDC on the compression stroke, i.e. just prior to the exhaust valve opening, before torqueing the corresponding rocker arms.

There's basically zero chance of any issue with the 1.98 and Comp Cams rocker arms. They're designed to work together. Installed correctly, you wont have any issues. Well, unless you rev the crap out of it and then it's all bets off.

 

[Milesvtcalais]

I have to ask a question. It may be obvious but it's a mistake i made years ago with one of my first engine builds.

I have done this exact job you're doing with the 1.98 rocker arms and Comp Cams pushrods with no issue myself.

My question is, when you torqued the rocker arms did you crank the engine through the cycle so that each piston was at TDC with the exhaust valve rocking as you torqued it?

If not, that is your issue. Somebody touched on it earlier but what will happen is that because your cam lobes are at varying positions you need to rotate the crankshaft in to position to torque the rocker arms on the side of the cam opposite the lobes otherwise if either of your cam lobes are starting to point up towards the valvetrain then you're preloading the rocker arms, the valves wont all close and/or open properly and you risk valvetrain damage and more depending on other modifications. You must make sure that each piston is at TDC on the compression stroke, i.e. just prior to the exhaust valve opening, before torqueing the corresponding rocker arms.

There's basically zero chance of any issue with the 1.98 and Comp Cams rocker arms. They're designed to work together. Installed correctly, you wont have any issues. Well, unless you rev the crap out of it and then it's all bets off.

Hey mate, thanks for your reply
Yeah I torqued them all down when the other valve was fully opened and beginning to close, my sequence was turn the motor over with a breaker bar until one of the rockers was starting to close (let's say exhaust) and then torque down the intake side and repeat.
If this is still an issue let me know

 

[losh1971]

Hey mate, thanks for your reply
Yeah I torqued them all down when the other valve was fully opened and beginning to close, my sequence was turn the motor over with a breaker bar until one of the rockers was starting to close (let's say exhaust) and then torque down the intake side and repeat.
If this is still an issue let me know

It sounds like you atill haven't measured the preload? This is an important step as it helps with diagnosis of rattles and taps, if they present after rocker fitment.

 

[Milesvtcalais]

It sounds like you atill haven't measured the preload? This is an important step as it helps with diagnosis of rattles and taps, if they present after rocker fitment.

Would having the wrong amount of preload cause it to not be making the right amount of power? It feels really sluggish

 

[losh1971]

Would having the wrong amount of preload cause it to not be making the right amount of power? It feels really sluggish

if the valves aren't opening and closing properly then yes. Just because you have torqued them right, they still could have too much preload. You measure preload on each rocker to determine if you need different rods. It's time to take it all apart again and post the results of the preload measurements. Then you can figure out if you need shorter rods.

 

[07GTS]

preload is the stability of the valvetrain it needs to be right so when engine is cold its within range and also when it warms up n block n heads expand it stays within range,

 

[2O4TS]

if the valves aren't opening and closing properly then yes. Just because you have torqued them right, they still could have too much preload. You measure preload on each rocker to determine if you need different rods. It's time to take it all apart again and post the results of the preload measurements. Then you can figure out if you need shorter rods.

No argument with your post as far as loading up the assembly, what I'm struggling with is why the pushrods wouldn't be the right size. I'm running a decked block and shaved heads to the point I could just get the LIM bolts to align and running the same lifters and pushrods in an engine I've not long ago built and it fired and ran without issue first key turn. Well, I had a minor issue with intake restriction causing it to hunt initially but once that was sorted, all good.

I don't come on here very often and most people have either sorted their issues by the time I'm having a browse or are working on suggestions and I have nothing to add but this reminded me of something I did as a teenager, way back last millenium. Actually I reckon you yourself might've given me a bit of advice once or twice a few years ago. Anyway this has got me scratching my head and wondering if some other issue has cropped up. If it was a cam and lifter job, different story, but that combo, it's sold together to work together and really, while sure, I know it's always wise to check your clearances, if what the OP bought off Gumtree is the matched rocker and pushrod assembly Mace supply and the pushrods haven't been swapped for a different size there really shouldn't be any issues. It's literally a bolt on.

I took a tonne of pics during my build then lost them all when my phone and laptop shat themselves the same day or I'd have a look at the part number/size on those pushrods for comparison.

OP could soon see the length (from memory it's printed on them) or part numbers on them if he's taking off the rockers and call Mace and double check *Edit, found this. See below.

Based on everything I've read that he's done, in my opinion it can only be that either the pushrods supplied weren't the correct matching length pushrods or the issue is unrelated. If he torqued his rocker arms to spec with each of the cam lobes pointing 180 degrees from the lifter then he has effectively set his pre-load correctly. Pre-load as you know is generally determined immediately prior to the valve opening but frankly as long as the lifter isn't on any part of the ramp on the cam lobe you're achieving exactly the same thing.

I was taught, "Number 1, top dead center with the exhaust valve rocking" (to start) which was all the information I needed after my little FU as a kid but I don't know the experience level of the OP so my way of explaining it I realise might seem somewhat obfuscated to someone with a technical background but was intended for someone less experienced but ultimately, it's the same thing.

To the OP, if you are certain that you weren't preloading the valves when you torqued the rocker arms and the torque is correct I can only see two possibilities. 1, the pushrods are not the ones normally supplied with the Mace 1.98 rocker arms or you have a completely different, unrelated issue in which case it's time to go back to basics. From what I've read and your reply to me you really should only need to pop out one pushrod .

*Woah, stop the presses. I just found something very helpful for you. Your pushrod length should be 7.050" for those rockers. If they are and you definitely haven't torqued them with extra load by having the cam in the wrong place while torqueing the rockers down, that is definitely not your problem. Don't discount the possibility that somewhere in amongst those dozen rockers you've torqued you've made an error with the camshaft position in even one of them. If you have 7.050" pushrods and you've torqued everything properly, not just to the right torque setting but with a 'correct' procedure so you're not pre-loading the assembly as Losh and others have mentioned then it simply isn't your problem.

 

[losh1971]

I feel the OP may be loading up the lifters because he had the valves open before. I suggest the OP goes over them one by one and measures the pre-load. He needs to set the wrench and then check the turns, starting with the rocker bolt just on the point of grabbing, using fingers to feel it hit. Then once the tension on the bolts is set and we know the number of turns we can figure out where to next. Get this done first and then we can look at other possible problems.

 

[losh1971]

Issue is without measuring preload we are only assuming the heads haven't been shaved or the block decked or an aftermarket cam not fitted and that everything is within spec. Do the former i mentioned above and go from there. He could have a stuck lifter as is reasonably common but until preload is checked we are simply guessing. Mine developed a rattle afterwards but I had to go through the entire process over to figure out where to. It took me days to figure out the issue and then four weeks at the garage fixing the problem, two days work that took weeks before I got the ute back.