I am rebuilding a pair of 575 SCI for a friend. Things are moving along well to this point. I am a bit confused as to what is the correct timing chain and gears to use. The reason for my confusion is that the blocks are Gen VI , but the cams didnt have the usual Gen VI step nose, they are old style Mark IV. I called Cloyes today to talk to tech, I explained my issue, after a long silence, the techs answer was to use a standard Gen VI chain and gear set. So, I ordered these...

http://store.summitracing.com/partde...9&autoview=sku

After thinking about this for a while, I am not so sure they will fit ?? I know I cant fit a double roller , because of the chain cover. The OEM Merc chain and gears from Merc are way over priced. What will work?

comp cam part number 241 for timing cover conversion
(Gen V cam install into a GEN VI Block.) If interested I have the part number for a new double roller that fits the GEN VI

www.mefituning.com

Just my luck, those chain set ups didnt fit. I knew it wouldnt. That guy at Cloyes must have been the guy who usually sweeps the floors. Most likely, everyone else is at The P.R.I. show. After calling everyone who makes timing sets, it seems I need a standard Mark IV set up. Only problem, nobody makes a single roller. I ended up ordering a pair of Comp Cams link belts. Not a big fan of link belts, but thats what was in there from Mercury.

The mercury part # for the chain is 845796t

it's used here
http://www.mercruiserparts.com/Show_...K+AND+CAMSHAFT
502 mark IV engine

here too
http://www.mercruiserparts.com/Show_...k+And+Camshaft
500EFI ( hyd roller)

and this is the 575SCi
http://www.mercruiserparts.com/Show_...k+And+Camshaft

They're calling it a "single roller"

All 3 crank sprockets are the same #

The gen IV 502 and the 575 cam sprockets are the same #
the 500 EFI ( hyd roller) isn't...prob. due to step on cam nose??

That same chain is used in 454/502 gen VI engine too
http://www.mercruiserparts.com/Show_...K+AND+CAMSHAFT

One would think that it came out of a GM parts bin,
somebody in the aftermarket world would have
copied it ??


Vinny,
I'm just getting started on doing a refresh on my
own 575's...and since you're well into your project,
if you run into any more issues like this, I'd like to hear
what they are.....and what you ended up doing.

JaayTeee.......... The 575's Vinny is working on are mine....... I am not to mechanicly inclined so Vinny is handling pretty much everything......I am just getting lessons throughout the process..... I am sure he will chime back in and let you know about any bumps in the road that we have come across so far....... I am curious if you are rebuilding for a reason or like myself just overhauling before something major happens. Also are you adding any HP at all or staying stock...........?

Mine have 388 hrs on them, never been touched
other than normal maint. items.

I bought new cometic head gaskets this spring
because it probably was time to replace them,
but it got warm, and I wanted to go boating
so, that task got shelved.

Late this fall on the last time out, I noticed when
one of them was cranking over, a different cadence,
a limp, on one cylinder, it started and ran fine,
but I knew something wasn't right.

Comp. tested and leaked down.....not good,
pulled the engine in question out, tore it down, gasket was
pretty much toasted between 5 and 7, head and block
in that area have cleaned up alright though.

Bores look ok, haven't done much else to it yet,
need to get the other engine out before the building
that the boat is stored in gets snow bound.... and this
might be the weekend to do it.

Right now, I'm torn on what to do with them,
but I'm kind of leaning on just going back stock
with them.....I know it's easy to get more out of them,
but, their neighbors who live behind them haven't
been as maintenance free, and adding more power
could just amplify that problem.

They're, at the least, going to get freshened


Decisions....decisions.

JayTee,

I will be glad to share any information I have. If you have anything in particular you need, drop me a line. If you need, John has 2 sets ( 16 ) stock bore 4.470 OEM pistons, he wont need anymore. The blocks had to go to the next size, 4.500 for a clean, round cylinder. First thing to mention, we are not modifying anything. We dont want to mess around wth any kind of ECU re-mapping. We only tried to make subtle improvements to these engines. While the bores may have been able to be saved, we opted not to, for a few reasons. The bores were a bit loose, but coating the pistons would have brought the piston to wall back into specs. Another reason for boring and replacing pistons was to get away from the metric ring package Merc used. We went with a set of custon made Wiseco's. We sent a piston to them, they matched it exactly, just made them for a 4.500 bore. They have a -12 cc dish, had the blocks and heads milled down, just enough to flatten the decks and give a clean surface for the Cometic gaskets. I ordered a set of .051" Cometics, which will produce 7.72 compression. A bit more than the stock 7.5, but close enough. Speed-Pro rings, upper gapped to .022 , second ring to .024, standard tension oil rings.
A big hurdle were the cams. I wanted to replace the hydraulic flat tappets with hydraulic rollers. I talked to Bob Madera ( Rmbuilder ) to try to duplicate the flat tappet profile to hydraulic roller cams. After alot of trying, he coudnt copy them exactly. He said they could be closely replicated , "Most Likely ", close enough to not need any ECU re-mapping. John and I deciided that. " Most Likely" wasnt close enough, so I had Bob copy the exact profile to the best hydraulic flat tappet cores that were available. Not what I originally had in mind, but options seemed limited.
My current state is this.. blocks are done, pistons and cranks are in. Waiting for timing chains to set up the cams, to button up the tin on the short blocks. Heads are done, waiting for the Cometics. May as well give the low down on the heads. I used Crane 99890 springs, Crane 99972 steel 10* retainers, .050 offset locks. All new Rev valves, inconel exhaust. Set the springs to 1.950 @ 135 lbs on the seats, 350 lbs open.

For anyone who may need this infomation... The Comp Cams link belts fit with no issues.