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GT6 pushrods


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Hi all.

Big step last night, rebuilt my head and got it mated on the engine and torqued down nicely. However when I put the pushrods in and tried to slip the rocker assembly down it sits a couple of mill or two off the base of the head and is in contact with all of the pushrods, even with the adjusters fully open!

The head was just refaced so hasn't been skimmed to death, it has a hi lift PI cam but I cant imagine that making a huge difference. The pushrods didn't come with this engine, they came from my mk2 gt engine. End to end with a ruler they are about 206-207mm. Head is a 219015.

I'm guessing I need shorter pushrods, are there any standard ones that are shorter?

Thanks,

Jacob 

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Hi Jacob,

The cam shouldn’t affect the pushrod lengths.

Something is strange though. The rods from a Mk2 engine should be too short not too long as the 2.5 /domed piston 2L heads are around 4mm thicker than the heads for a flat piston 2L like the Mk2.

Can check lengths this evening, but in the meantime you might want to check that the cam followers are correctly machined. I read something recently where someone with a similar problem found that the rods weren’t sitting as far down in the followers as they should be.

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This might be a brainless suggestion, but if you only 'slip the rocker assembly' on I'm pretty sure it does indeed dangle above the head slightly. The pushrods corresponding to open valves will hold it up, until you tighten it down and the valves are forced open :) 

Or am I being daft?

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4 hours ago, Nick Jones said:

Hi Jacob,

The cam shouldn’t affect the pushrod lengths.

Something is strange though. The rods from a Mk2 engine should be too short not too long as the 2.5 /domed piston 2L heads are around 4mm thicker than the heads for a flat piston 2L like the Mk2.

Can check lengths this evening, but in the meantime you might want to check that the cam followers are correctly machined. I read something recently where someone with a similar problem found that the rods weren’t sitting as far down in the followers as they should be.

Nick, 

Ok I’m not completely insane then. I’ve had about 3 engines now so I’ve lost track of what bits have come from where but I’m fairly sure they where from the original one. Ah this does not sound too good. I’ll have poke down and see about the cam followers. I’m guessing they can’t come out now with the head on, it’s only been torqued down for a day now so surely if the head needed to come off I’d be ok using the same gasket?

I really hope it’s something simple with this that I’ve missed, otherwise it sounds like it’s game over. Bugger.

Jacob

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3 hours ago, PeteStupps said:

This might be a brainless suggestion, but if you only 'slip the rocker assembly' on I'm pretty sure it does indeed dangle above the head slightly. The pushrods corresponding to open valves will hold it up, until you tighten it down and the valves are forced open :) 

Or am I being daft?

Pete, yes I was wondering this myself, no1 is at TDC so surely some valves are wanting to be opened, hence the resistance but surely with the adjusters on the rocker arms fully open you’d expect some slack and not contact with the pushrod. With times like this I wish I stuck with minis!

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https://www.triumphclub.co.nz/?page_id=653

If you scroll down to the bottom table it has push-rod lengths listed.  Sounds like you have the 8 1/8" ones, which match your 219015 head.

To pick up on Pete's point, it doesn't matter where you set the crank position, you won't get all the push-rods slack at the same time as some of the valves will want to be open and that means the springs will have to be compressed as you tighten the rocker shaft down.

My technique for install is to drop all push-rods in and make sure they are seated in the followers.  Put a drop of oil in each push-rod cup and then fit the rocker assembly loosely onto the studs.  Next, work along the row, uniting each push-rod cup with it's respective adjuster ball.  Then fit the hardened washers to each rocker stud and screw the nuts down finger tight.  Now work along with a spanner tightening evenly and gradually, taking several passes to snug the pedestals down onto the head surface. No great force should be needed. Do keep an eye out for problems - especially making sure that the valves that do want to open do not try to open to the extent that the springs get coil-bound.  Stop if it looks like this could be happening.

All being well you'll be left with about 1/3 of the valves being partly compressed and the others still being slack (assuming you have the adjusters wound all the way up).  The slack ones might still be slack enough to fall out.  Now wind the adjusters down on the slack ones and ll being well you should find the slack disappears about halfway through the range, proving all is well.  You can now set the clearances in the usual way, rule of 13 or mirror about the centre (latter is my favourite as 13 is a scary big number and I only have 10 fingers)

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12 hours ago, Nick Jones said:

https://www.triumphclub.co.nz/?page_id=653

If you scroll down to the bottom table it has push-rod lengths listed.  Sounds like you have the 8 1/8" ones, which match your 219015 head.

To pick up on Pete's point, it doesn't matter where you set the crank position, you won't get all the push-rods slack at the same time as some of the valves will want to be open and that means the springs will have to be compressed as you tighten the rocker shaft down.

My technique for install is to drop all push-rods in and make sure they are seated in the followers.  Put a drop of oil in each push-rod cup and then fit the rocker assembly loosely onto the studs.  Next, work along the row, uniting each push-rod cup with it's respective adjuster ball.  Then fit the hardened washers to each rocker stud and screw the nuts down finger tight.  Now work along with a spanner tightening evenly and gradually, taking several passes to snug the pedestals down onto the head surface. No great force should be needed. Do keep an eye out for problems - especially making sure that the valves that do want to open do not try to open to the extent that the springs get coil-bound.  Stop if it looks like this could be happening.

All being well you'll be left with about 1/3 of the valves being partly compressed and the others still being slack (assuming you have the adjusters wound all the way up).  The slack ones might still be slack enough to fall out.  Now wind the adjusters down on the slack ones and ll being well you should find the slack disappears about halfway through the range, proving all is well.  You can now set the clearances in the usual way, rule of 13 or mirror about the centre (latter is my favourite as 13 is a scary big number and I only have 10 fingers)

Nick, thanks once again, I'm going to follow this today and will report my findings. Hopefully I'll come back shortly with no dramas.

Thanks again,

Jacob

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Ended up getting a bit pre occupied yesterday annoyingly. Just tightened the rockers down and absolutely no dramas. No binding or horrible things occurring.

Going to take my time going through the clearances but all is looking good so far! I think I was worried about nothing!

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All sorted hopefully, just done the clearances and checked through them a couple of times. It's so nice only needing one feeler gauge!

I'll be putting oil in later on and doing a compression test!

Getting closer and closer to engine start!

Thanks once again for all the help

Jacob

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