Riser inspection for 1975 Aristocraft 19 with Merc 165 I6

[sookie]

I have a 1975 Aristocraft 19 with a GM mercruiser 165 I-6. The exhaust elbow/riser gets too hot to hold my hand on it
( 185*). The rest of the manifold is comfortable to touch and water exiting at the prop is pleasantly warm. The engine is installed so that there is only 1/4 to 1/2 inch between the riser and the rear deck of the fiberglass hull. Lifting the riser up and off the posts looks to be impossible. My question is do I need to remove the whole exhaust manifold to inspect the riser. The previous owner has put thousands into it and it has limited hours since a complete (?) rebuild was done a few years ago. It has a san juan closed cooling system.

I'll post pics in a couple of days if it helps but at the moment it's snowing.

 

[MikDee]

Re: Riser inspection for 1975 Aristocraft 19 with Merc 165 I6

Sometimes the impossible is possible. Everything on most boats is tight. Why don't you try and remove the elbow, maybe you can roll it out back, forward, or sideways, while prying gently on the fiberglass. There is some play in the boltholes, as long as you can get any rust out. maybe you could even lower the motor a bit on it's mounts. Either way, nothing ventured, nothing gained.

If you think this is tight, I hope you never have to replace a marine starter

 

[sookie]

Re: Riser inspection for 1975 Aristocraft 19 with Merc 165 I6

Thanks, MikDee. I am new to inboards and I'm seeing that access to many jobs borders on the ridiculous. My problem may be specific to the Aristocraft 19 with just the Inline 6. Lowering the front of the motor will not necessarily give me enough room and then I'd likely have to have it aligned. The fiberglass is quite stiff and has a stringer a few inches in from the edge. Cutting a notch into the back deck would be a last resort although I could just make an access hatch out of checkerplate. I've got easy access to the manifold but why go there if I don't have to.

More damn snow so I'm off the project for a few days.

 

[renojim]

Re: Riser inspection for 1975 Aristocraft 19 with Merc 165 I6

It is very tight on a 19 back there. I struggled with this on mine as well. The intake/exhaust manifold is held on with mostly bolts, but there are two studs. So for that reason you can't pull the manifold off sideways because the rear fiberglass structure doesn't give the clearance needed. You said the engine has been rebuilt recently. You might be able to double nut the studs to remove them then unbolt the manifold and slide everything forward and out. This is definitely a two man job, that sucker is heavy. When I did mine I pulled the entire head and manifold as one, veerrry heavy. I wanted to mill the head for more compression (we boat at high altitude,) but that's another story. If they won't remove you could try very carefully to cut them with a Sawzall. Be very care not to nick either surface. Buy two new studs and slide them through the manifold when you reinstall it. While you have the manifold off have it checked for warpage and possibly resurfaced. Only use a Mercruiser gasket. I found this out the hard way. I rebuilt the engine and smoked #2 cylinder after only 20 hours. Small vacuum leak on the bottom of the intake surface. Also while you have the exhaust off check the rubber flapper and make sure that both halves are there and pliable. It's located just below the rubber exhaust hose. This piece keeps water from coming up the outdrive and into the engine. Might also be a good time to replace that old stiff and brittle rubber hose. A new hose is much more pliable and makes the manifold install much easier.

 

[ziggy]

Re: Riser inspection for 1975 Aristocraft 19 with Merc 165 I6

The exhaust elbow/riser gets too hot to hold my hand on it
( 185*)

while i don't have a closed system. i'd think that's pretty close to high end of normal operating temp. i's assuming ya got a 160* tstat (for closed sysem). from what i get about tstats. the temp stated (160*), is when it starts to open. + 20* or at about 180* the tstat will be full open.
granted yours is running at the high end. but perhaps that's normal for an aftermarket closed cooling system...
here's a little read on the subject.

just food for thought.

 

[sookie]

Re: Riser inspection for 1975 Aristocraft 19 with Merc 165 I6

Thanks fellas,

I now know what I'm in for eventually. After reading up on engine temperatures with a Fresh water system I'm going to monitor the riser temperature under a number of different operating conditions and keep a log. If it doesn't creep up above 185* then I'm putting this job off.

I'll update this thread when it warms up and I get the boat out for a rip. If anyone else has any other words of wisdom for this job I'm all ears

 

[ziggy]

Re: Riser inspection for 1975 Aristocraft 19 with Merc 165 I6

imho, sounds like a good plan sookie. no point in doing hard work if it's not necessary. from what ya said in the first post, sounds like the previous owner did a lot of engine work to include switching to fresh water cooling. in my mind, it'd be hard to think that the po didn't do new manifold and riser when he did all that cooling system work. perhaps ya can even tell from the outside if it's a newer manifold and riser. many of them from that era have very visible rust on the outside if they're original. mine did anyways. on mine, a rusty on the outside manifold was a bargaining point for a lower sale price. and man, was i right. within a week of my purchase, i was getting water in my oil due to a faulty, rusty manifold. it was more rusty on the inside than it was on the outside.

looking fwd to hearing about your first 'rip'.
i'm also looking fwd to your pics. nineteens came in so many different flavors, it's cool to see all of them....

what color did you get?