Quote: Valid point, but I have seen one case where just one valve was touching a piston, & I mean only 'just' touching. Enough to leave a witness mark but not enough to actually do any damage & it was noisy, but I suspect that L18_B110 is probably closer to the truth, & I made some reference to this in my first post.

Yep, 1mm piston - valve clearance at assembly just isnt enough, 41mm valves weigh a ton, it's not a 16 valve engine with little light valves. These big old things really move around at speed..
Take the small hit in compression ratio and put deeper pockets in your pistons IMO.
Also, the stock pushrods bend like you wouldn't believe. Put a dial gauge against the side of them sometime... Now think about it all happening at 7000rpm.
Just putting in decent pushrods makes a huge difference in the effective lift at high rpm.

I race with some one that runs a ford escort mexico with a 1600 pushrod engine with large valves and high lift cam he was having the same problem the engine was designed to run to 8500 rpm . he put new valves in and found the engine would only rev to 7600 rpm and fall flat the hotter the engine got the lower the rpm it would turn. turned out the new valves weighed more (7 grams) and the spring rate was insuficent to close the valves causing valve float and evential engine failure. I believe with the extra lift your valves are floating and you may need to increase your spring rate.

So what happened with this?

It seems like these roller rockers should be good upgrade, and nearly manditory for anyone with double valve springs...

Ok. I also think the problem is valve bounce, the Rolla Rockers actually weigh 10g more than standard. Jeff Taylor thinks the clearance isn't the problem but he uses a relatively light double valve spring. I will try some heavier spring later. but for now just leaving it as it is.

it's good that it's not a problem in the rockers, I want some, that did they run and what else is needed? ( proper length pushrods for one )

can any one tell me the length of the a14 push rod and where i can get a set and what do the rolla rockers go for

Sorry I dont know the length of an A14 pushrod, but if you want to know the price of the roller rockers contact Yella terra below.

sales@yellaterra.com.au

I'm seriously thinking about taking off my roller rockers and going back to standard, why...just after I installed the rollers (18mths ago) i started having the same problem as rally1200, a ridiculously annoying miss about 8000rpm, then the miss came down in rev range till about 6500 rpm, at this range my motor was just starting to make some good horsepower then it would sound like it was valve bouncing.

I tried everything from changing valve springs to timimg to fuel to different coil etc etc.

I fronted up to about six rallies with this problem, couldn't find the problem.

Anyway after last years round of the ARC the motor would not rev over 5000rpm for the two day event.

So after the rally I pulled the motor down to see what the problem was and found that the lobe had worn off No.3 pot inlet side of the cam and the lifter was totally F***ed. Never had this problem before so I thought oh well these things happen, put new cam in and rebuilt motor.

Thought that was the end of problem till after the last two rallies I've had to adjust noisy tappets, the same tappets.

To cut a long story short, blew a head gasket, took head off, dial indicated lift of cam and found that three lobes are worn by .5 to .75 of a mill, haven't taken sump off yet to confirm.

Now I've been mucking around with the A-series for a long time now and I've never had this problem before.

Is it coincidence that since I've had rollers on that I'm wearing out cams? Dunno...but if the lobes/lifters are worn again I'm going back to standard lifters and see if I have the same problem.

Quote:
What lifters have you been using up to now? I was thinking of splashing out for the 'weight reduced' type at about $50, ......... each, but if this is what you have been using, then maybe not.

Who does your cams?
Some grinders moly bake, or otherwise moly treat the freshly ground lobes to minimise wear, particularly during the break-in period.

It would seem that the increase of rocker ratio from 1.44 to 1, out to 1.54 to 1 would not be enough in itself to cause any dramas, & the low friction of the roller bearings & roller tip could only be an advantage, so even if the rockers are a little heavier than the stock ones, it still seems difficult to grasp that they might be linked directly to lobe & lifter wear.
The lack of side thrust on the valve tip due to the roller-end on the rocker must surely be a benefit to guide wear, particularly with shortened guides in a race head.

I'm looking forward to the follow up on this.