fred

I am having trouble on one of my 454/400 Cyclone motors, it has broken two poly-lock rocker nuts, the motor has the crane gold roller rockers, the nuts have been broke on both heads, now I have a cam that has went round on one lobe, the engines were rebuilt prior to me buying it and have ran well all last season and most of this season untill the recent nut breaking...I don't have the paperwork from the engine rebuilder so I don't know if the cams were replaced or not, what I am wondering is if the cam has just wore out or did they replace the cams and springs or just springs and went too heavy on spring pressure?...the springs are double springs...Coil bind doesn't appear to be present although it looks fairly close....there is still gap between coils at wide open valve...but not a whole lot, anyway do you have any ideas prior to me pulling the engine apart to see what cam is in the motor?....Thanks Fred

Dennis Moore

I have no idea why the Poly Locks would have broken unless they were too tight. Make sure that the tops of the rocker studs are perfectly flat for the allen screws of the poly locks to tighten against.

The camshaft going flat is usually caused by the lifter not rotating in the lifter bore. Usually a problem when old lifters are used on new camshafts. Inspect the bottom of all of the lifters and see if they are flat or still retain some crown in the middle. They probably are worn out and have concave bottoms. I would think that they would all have gone bad if the spring pressure was too strong.

When the rocker arms are removed, check to see that all of the studs in the heads are straight. Check to see if any of the pushrods are bent and inspect the valve stem tips for unusual wear. Check to see if the rocker arms were contacting the valve spring retainers.

Regardless you will have to replace the camshafts, don't go with the original camshafts, they were not a good choice by Mercruiser in the first place. To be safe you should replace the camshafts, lifters, pushrods and valve springs.

Have someone knowledgeable inspect the rocker arms or call Crane Cams Tech Line and ask them what to look for in rocker arm wear.

Use a camshaft with moderate lift. The horsepower difference will be minor and you won't have to worry about installing longer pushrods to maintain the correct valve train/rocker arm geometry.

Converting to roller lifters would be best if you do a lot of idling in a no wake zone. Strong valve springs, high lift camshafts and stiff valve springs will wear out flat based lifters really fast.

With a double pumper Holley carb you need to change oil every 25 hours. The oil gets diluted with raw fuel (from the accelerator pumps) and loses its lubrication properties.

Good Luck
Sincerely
Dennis Moore

fred

Thanks for the imput Dennis,....I will continue on with the tear down and let you know what I find...do you think a double spring set up is needed in this application?...seems like a lot of pressure for low rpm motors......I have a hunch that the original cams may have been used and the lifters put in the wrong bores....or possibly a soft cam?....I hope the lifter will still come out from the top if it's not mushroomed....also any ides of what casting # 02728 may be? I have that # inside the valve cover opening on one motor.....no idea what it is other than a GM factory cast iron head.....Thanks, Fred