Hi folks - bit of a head-scratcher. Got the head on, timing marks are aligned (I've got them exposed), only got the inlet pushrods in (outer followers) but engine jams. Rotates freely otherwise. Looks like the pistons are rising as the inlets open which doesn't make sense. Are there two keyways on the cam or crank pinion? Marks on the idler seem symmetrical so assume reversing them wouldn't make any difference.
Hi Wardy,
A bit of a puzzler. There is only one set of keyways and if the marks are lined up then that should be it. Unless you have a very high lift cam and high comp. pistons the valves should not make contact with the piston. So with the inlet push rods in place the engine jams but without them it turns freely indicating the problem seems to be with the push rods.
A bit of a long shot but are the push rods too long and causing the valve springs to become coil bound?
Dave.
I would check that the pushrods are connecting with the outer cam followers. It's difficult to see them and easy to get one on an exhaust follower. Erhum..... Dont ask me how I know this........
Chris
Thanks folks. I'm happy the pushrods are on the right followers, not sure of the camshaft, pistons are 9:1 std. Thought there was only one length of pushrods, will measure and see if that helps, and check if the coils are getting solid.
Act 1 scene 3 - springs not coil-bound. Are the inlet and exhaust rockers dimensionally different? Thinking about leverage
Hi,
All the rockers have different part numbers with the inlets being mirror images of each other and ditto the exhaust rockers. The inlets and exhaust rockers are different and I would think not really interchangeable. If I remember correctly, the exhaust push rods are a bit longer than the inlet.
Dave.
:) :) :)
Rockers definitely not interchangeable--this aspect is worth a look. If I remember rightly the inlet rockers are the short ones.
Mike 8) 8) 8)
Now more bemused than before. The rockers seem correct, (exhausts are marked 68-152 and 68-154) bizarrely the engine rotates freely with just the exhaust rockers/pushrods installed, but locks with the inlets installed. As far as I know the only involved components that have been changed are the pistons and valve springs, the pistons were std 9:1 from C & D, and the valve springs are not binding (the exhausts are OK and I'm assuming the inner coils won't bind before the outers). As far as I can see the pistons are symmetrical in terms of valve cutaways etc.
Good morning Wardy,
Have new valves/valve guides been fitted? If the valves are a bit shorter and/or the guides a bit longer, then the top spring retainer could be contacting the top of the valve guide. A bit of a long shot but worth a look.
Dave.
Thanks Dave but all unchanged. Only change factor as far as I know is the pistons. Will carry on playing with it!
Hi,
I am intrigued by this now. If the valve is touching the piston this should be just about visible looking in the spark plug hole. Also try with a lot of gap on the tappets. With standard at 8 thou try some thing like 25 thou or more. This will reduce the lift effect of the cam so the valves will not open as much.
What pistons were in before? If lower compression were fitted could the head have been over skimmed so now with 9:1s some contact is being made?
Dave.
:) :) :)
Please don't feel insulted by this but I recall having a similar situation and the cause was having the pushrods in the wrong place. Are your push rods actually the right length.
Very interested in the outcome to this one.
Mike 8) 8) 8) 8)
:) :) :)
Further to my last: -have you tried the rods individually to see if it is only one thats causing your problem.
Mike 8) 8) 8) 8)
Hi guys - I've measured the inlet pushrods, they're identical at 6 3/8 which is what the book says. What is apparent is that it's more difficult to get the TS one in than the DS one, even backing the adjuster off completely, so I'm going to take the inlet rockers off and see what that throws up. Only clue I have at the mo. Can't be head skimming I think as the exhaust side is fine, and the head gasket I have is thicker than the one that came out.
:) :) :)
Hi
Have you solved it yet?
Mike 8) 8) 8)
Hi Mike - no, birthday has prevented me getting to work on it for a couple of days. Will be back before long. Thanks
Right - tore it all down and rebuilt it carefully, and it's OK now. I think the cam pinion was not aligned with the keyway (must have knocked the key out tapping it onto the shaft, as I couldn't find one when I pulled the pinion off). This is of course not apparent externally. So the moral of the story is - check. Thanks for the various suggestions nevertheless.
:) :) :)
Thats brill and thanks for the follow up. Might just save someone else a bit of trouble and heartache???
Mike 8) 8) 8) 8)
Followed the Sherlock Holmes principle. If you eliminate what is impossible, whatever is left, however improbable, is the truth. Had to be crank or cam pinion, as everything else is a constant. Lucky in a sense that the position it finished up in didn't permit it to rotate in a "wrong" position, as it were. Hopefully it may avoid a repeat for someone else.
Can you try assembling it either with the adjusters wound right off, or even better without the rockers? You can then compare the height of each pair of pushrods at maximum lift. Does it still spin OK now?
If this hasn't resolved the problem an alternative might be that one of the valves is binding in it's guide - I'm afraid it will be a head strip to check this..........