QUIKDECISION

I have a 1988 454 Mark IV Magnum engine that I installed a Gen VI
bull nose roller cam into. I did this because the cam retainer plate bolts right into the block thus no need for a cam button. The brand new Gen 6 timing chain is loose. THese are the Gen Vi Timing chain and gears.
I have about a 1/2 inch play in the chain. This is the 2nd new set that exhibits the same problem. Is the distance from the cam center to crank center different in the Mark 4 as compared to the Gen 6

HPJunkie

I had to line bore a gen V 502 block and the chain was loose too. I have a gen 6 cam and didnt want to buy a new cam. THE only company that makes an undersize chain is cloyes. Teague told me this and I called cloyes and they had 3ea .0005 under chains in the third week of Mar. I bought one and someone else bought the other. There might be one left. I do not know how to measure which one you have, but they do make a .010 under also. The problem is that these are not Regular produntion pieces. It sounds like they mix and match from production tolerences. Anyway call cloyes right away. Greg

QUIKDECISION

Gregg Thanks,
I'll call them.
Doug

mrhorsepower1

This is a very common problem on the Gen 6 engines. Even if your block has never been align honed, the chains are loose. The problem is in the chain and gear set up. Cloyes DOES NOT offer a -.005 or -.010 under chain set for this application. The only way to correct this is to run a Mark 4 style camshaft. Scott Shafiroff Racing offers a Gen 6 timing cover that will allow you to use a Cloyes True Roller timing set with dual roller instead of single. It is a very nice piece and includes locking plate, roller cam button, and a Tavia timing pointer. (about $225.00) The cover is thicker so if your running a circulating pump it will have to modified. If you are running a crossover style inlet, you will be fine.

HPJunkie

MR horsepower, I believe you are correct that the chain is a single roller or single row, just like the stock style chain and gears. Cloyes does offer that chain, Part # 9-3149-A which is a 005 under gen 6 upper sprocket. The reason I could use that part is the timing cover on the gen 5 will cover the gears and I am not sure but I think the stock gen 4 cover will not cover the gears,thats the reason I used the gen 6 cam and the stamped cover. I had 2 weeks to ready for the dyno date and did a lot of calling (4 straight hours worth) and I learned a lot. Greg

HPJunkie

MR by the way if Quick is starting from scratch the gen 4 cam is what Id buy too.

BillK

Quick,
A lot of the Gen VI chains are a bit on the loose side, but I have not seen it hurt a thing. I have actually started using the new style cams on all the Big Blocks, I prefer the retainer plate system compared to having to mess with a cam button. I am assembling a GenIV 468 for one of my part time helpers as we speak and that is what we used. I have not put the chain set on yet but it has been align honed. I checked clearances today and bolted the crank in place so I should get to the cam on Monday. Will let you know if the Cloyes True Roller set is loose or not.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

rws

On my Gen VI 540 I used a mark IV cam and timing chain ,because I already owned them.I bought an Imco Gen VI cast alum timing cover for about $80.00 and I did have to modify it slightly to clear the double roller (cloyes hex adjust) and I did have to machine the cam button to achive proper cam end play but it was the most economical route for Me.

BadDog

I sent my engine in for a full rebuilt early last spring. Ended up being down all summer waiting for a .005 short timing chain and gear set. Yes, Cloyes does make sets for the Gen6 but none were available until September.

Bummer. I will be buying one in advance and keep it with the boat. I may not need it any time soon but if I sell the boat or engine the part will be on hand for future use.