My little 4 cylinder timing chain set

Beck · January 08, 2016, 12:12:47 AM

You can't believe everything you read on the 'net.

I heard/read somewhere that my little Mercruiser 3.7 used a combination of timing set parts. The story was it took a SBC cam sprocket, a Ford FE crank sprocket, and one of the two chains. After searching all day I cannot find anything that shares the cam sprocket. It isn't SBC.

The sprocket has 3 bolts and a locating pin. The bolts are 1/4-20. They are allen head and countersunk into the sprocket. The back of the sprocket is set up to use a thrust plate bolted to the block so the back side is different than the SBC also.

I was banking on the top sprocket being a SBC. I intended to use a bolt on 1/2" hex spud to drive a timing cover mounted external oil pump. The sprocket mounting bolt diameter is just slightly smaller in diameter than the SBC. I was considering drilling out the holes to match the SBC but there will be a little slop in the counterbore for allen heads. I would also have to take a small cut from the face of the sprocket. It is rough cast now.

What would be the most precise way to enlarge the holes? Using a drill they would stay the same bolt circle. I need it just a hair larger. Using a mill? My skills aren't good enough to get everything centered.

I really wanted to use an adjustable top sprocket. I guess that's out...

enjenjo · January 08, 2016, 06:12:51 AM

QuoteWhat would be the most precise way to enlarge the holes? Using a drill they would stay the same bolt circle. I need it just a hair larger. Using a mill? My skills aren't good enough to get everything centered.

The obvious answer is to find some one with better skills.

From looking at pictures, it appears that the sprocket pilots on a counterbore rather than the bolts. If that is the case, you could make a fixture that uses the pilot to hold the sprocket in position, and an end mill to relocate the hole.

UGLY OLDS · January 08, 2016, 11:05:51 AM

I might be missing something , but are OE parts not available to start with :?:

Bob..

WZ JUNK · January 08, 2016, 12:38:51 PM

Tom, have you talked to Doug? He had to go through all this because he changed the deck height of his block.

John

Beck · January 09, 2016, 11:30:00 PM

Ugly Olds - There are aftermarket timing sets available. I would have liked to install a set with one of the sprockets adjustable. I also was looking for a way to drive the external oil pump drive direct from the cam.

Doug Lee did his with a belt drive from the cam. I will need to change my plans to a belt drive also. I am leaning toward a crank drive belt system currently.

John - I emailed Doug a few days ago, but he has not responded yet. I still want to make a trip there to see his car/motor.

WZ JUNK · January 10, 2016, 09:23:44 AM

Quote from: "Beck"Ugly Olds - There are aftermarket timing sets available. I would have liked to install a set with one of the sprockets adjustable. I also was looking for a way to drive the external oil pump drive direct from the cam.

Doug Lee did his with a belt drive from the cam. I will need to change my plans to a belt drive also. I am leaning toward a crank drive belt system currently.

John - I emailed Doug a few days ago, but he has not responded yet. I still want to make a trip there to see his car/motor.

Doug will be out a lot the next few days. He has a booth at the "Chili Bowl" event a Tulsa. http://www.chilibowl.com/schedule/ Last week they had the micro midgets running and he was down there some for that event. 1100 race cars in one building.

John

Beck · January 10, 2016, 10:09:25 AM

The Chili Bowl is on my bucket list. I will have to do that soon. I didn't realize it was that time already.

wayne petty · January 15, 2016, 03:51:45 AM

rotary tables can be had cheep.. if you have a drill press..

http://www.grizzly.com/search?q=%28table%29+AND+%28category:%22Rotary+Tables%22%29&rankBy=price+asc

if you have a vertical mill.. you might be able to use the table to locate them

this is just a thought of how to drill a round pattern on a flat object..

the rotary table might also be handy for making wheel bolt pattern redrill jigs..

Beck · January 15, 2016, 08:52:13 AM

I am abandoning the direct cam drive option. I am still considering using a belt drive from the cam. Doug used this method on his motor. The drive with the least fabrication is a belt drive from the crank like most use. There are available parts to make this a bolt. Any belt drive I use will require me to make mounting brackets for the remote oil pump.