Rebuilding Mercruiser 165 - GM 250 I6

[ethan169]

Somewhat recently I picked up a 1981 Glastron SSV-177 with a Mercruiser 165 I6 in it. I dont have a lot of previous information on the boat. I performed a compression check and found low compression on a few of the cylinders. I pulled the head and cylinder 6 looks like it had water in it. I looked for signs of cracked block or head and couldnt find anything. I pulled the engine out of the boat a few days ago to take a closer look since it needs to be replaced or rebuilt anyway.

Im pretty handy with engines but have never built a bottom end before. Ive rebuild/modified a few heads in my day but never anything in the short block. This looks like a great candidate to start!

Im looking for advice one what to look for and how to go about things. A few pics to provide visuals...

Heres the boat pretty much the day I brought it home this spring



This is what I found when I pulled the head with the engine still in the boat. As you can see cylinder 6 looks pretty gross. For the most part the other 5 look to be in decent shape... but what do I know?



Engine is out



Here is the engine on the stand with the head removed. From left to right cylinder 6, 5 and 4.



From left to right cylinder 4,3,2 and 1

 

[ethan169]

New post to break things up a little..

Here is the bottom end with the oil pan removed so we can see the crank and other components.

From left to right cylinder 6 and 5. I was concerned about how long water was sitting in the oil pan and what level it was at. I wasnt sure what condition i was going to find things in. I did know that the engine wasnt seized of course since i was able to turn it over no problem during the compression check. Cylinder 6 crank area looks like it may have had a little contact with water but for the most part looks fine? The rest looks good to me. Again but what do i know?


Here is the entire bottom end


Here is close look at one of the cylinders (No. 3)


It looks like someone rebuilt this motor and possibly didnt run it for very long. With a quick search online it looks like these cylinders are From sealed power P/N 295AP. Here is a link I found that gives me this impression anyway, http://www.summitracing.com/parts/slp-295aper

From the markings on the cylinder is it safe to assume this engine has been bored .060 over? Everything looks pretty fresh on this motor which is why I feel like its been redone recently (in motor hours) and then something went wrong? Even the head gasket looks new to me!

What can I do with this block to get it back to good condition? Ive seen rebuild kits that are around $300-400 that include new bearings and pistons. What would you move be here? Im looking for opinions from people who have rebuilt short blocks before.

The other question is what should I do if anything to the head? I figured at least replacing the valve stem seals? Should be easy with the head off. If brought the bare head and block to a machine shop what would I even ask them to do?

Thanks for any advice!

 

[alldodge]

I don't see any manufacture making a .060 over piston. I do see the .060 on the piston top and if it actually is 3.935 then I would scrap the block. Pistons for the inline 6 were: 3.8750 (original) to 3.9059 (.030 over) according to manual No 6.​

http://boatinfo.no/lib/mercruiser/ma...ser1.html#/438

My suggestion would get a bore gauge or telescoping gauge and measure the bore. Otherwise take the block and head to a machine shop and have them measure it for you. If the components check out, have them pressure test both before proceeding.

 

[Bondo]

I don't see any manufacture making a .060 over piston. I do see the .060 on the piston top and if it actually is 3.935 then I would scrap the block. Pistons for the inline 6 were: 3.8750 (original) to 3.9059 (.030 over) according to manual No 6.​

http://boatinfo.no/lib/mercruiser/ma...ser1.html#/438

My suggestion would get a bore gauge or telescoping gauge and measure the bore. Otherwise take the block and head to a machine shop and have them measure it for you. If the components check out, have them pressure test both before proceeding.

Ayuh,.... I gotta disagree with ya this time,.....

Ethan, go find a runnin' 4.3l in a Rotten hull, 'n transplant It into yer boat,....

Use the flywheel cover off yer I6 on the V6, 'n build up some front motor mounts,...

If that motor's already over-bored .060",... It's Scrap,.....

 

[ethan169]

hmm. Well i cant seem to find my calipers to measure the bore... Maybe tomorrow when im more awake ill be able find them and get an accurate measurement. However I measured it with a linear scale (ruler..) that reads 32nd's of an inch. I did my best and it looks like 3 28/32 which happens to be 3.875". All dodge is right I cant find a manufacture that has a .060 over bore piston. So perhaps its not bore .060 already. Ill have to do some more research on the pistons that are in there and get my calipers to get an accurate measurement of the cylinder bore.

Ill report back with what I find.

It would be nice if this long block was salvageable. It would be a shame to have to find another engine for this boat. Everything in the package is so clean and solid besides the obvious.

 

[Fishermark]

I've rebuilt a few of those engines and they are easy to work on and are good long lasting engines. I would not automatically assume the worse for this engine. It is important to get someone to measure and evaluate the bores. You might get away with honing and new rings. A machine shop should be able to tell you pretty quickly.

 

[bigkahuna427]

I am new here but not new to engines as I am a retired Master Auto Tech. That engine was made by GM when god was a little boy. Those engine were pretty decent in GM cars and trucks in the 60s and 70s. They were NOT rocket engines but very reliable. If I were in your shoes I would pull those one or two cylinders and hone the cylinder walls to see the extent of rust. You might just get lucky! There is nothing wrong with a block bored .60 over but I don't believe you can go any farther. You can have the block sleeved too. This is something machine shops should be very familiar with. So if you have one cylinder that is too pitted from rust you could have it sleeved and install a standard sized piston. That might sound odd with one standard piston but it really does not effect anything and the engine should run just fine.

As for why they are rusty you must have had water intrusion. This could be anything from a head gasket, cracked head or block maybe even the water cooled exhaust manifold filling up with water and with the engine tipped up water running into the rear cylinders through the exhaust manifolds. The 4.3 might be a nice swap but the bolt up nature of the engine you have now has to have it's appeal. My experience with that motor in the auto world makes me think I would have one in a boat.

 

[ethan169]

Thanks for you advice and experience all!

I finally found a machine shop local and got some time to bring it by for an opinion. The place seems to be a father son operation and they were both very helpful and polite/professional which i find a huge pluss second to skill/ability of course.

Anyway they both looked at the block (its not fully striped right now since the crank and pistons/rod are still mounted). I measured the bore with a set of telescoping gauges and solid pair of calipers to the best of my ability. I got 3.935" +/- 0.002 or 0.003. This was in the good cylinders. He measured a few of the good cylinders and found them to be 3.935 with a 0.001" tolerance throughout the bore. He said he would like it if they were perfect but 1 thou wasn't bad at all. Cylinder #6 the super rusty one has some pretty bad pitting and in some places is over by a bit. 5-7 thou if i recall. There is the one cylinder with the major pitting and one other that is questionable but the rest look quite good and most likely only need a slight hone to restore. His opinion was that the block is worth keeping since most of it is in such good shape. with a preliminary inspection he mentioned that for sure he would have to sleeve the #6 cylinder and potentially the other one with the pitting. Ill strip the block and bring it back to him for a in depth inspection.

He also looked briefly for cracked areas and didnt see any. I also looked quite thoroughly but have never seen a "cracked block" in person... only a grenaded one..

So im going to finish stripping the block and bring it back to him and go from there.

Thanks again and ill keep anyone whose interested posted!

 

[ethan169]

A brief update.

I disassembled the block so the machinist could take a closer look and potentially do some work to it. While removing the connecting rod caps I noticed that one of them was on backwards. You could see the uneven wear in the bearing too. Once I got all of the pistons/rod out there were at least to pistons with the rings installed in reverse order. It was clear that whoever built this engine last didnt know what they were doing.

When I pulled one of the crank bearings there was a date code on the back side that was 2002. So its been sitting for some time. The bearings for the crank and connecting rods all looked like they were never really run. They were still that dull color and not really worn much. Id be willing to bet that this engine either never ran or ran for a very short time. Most of the wear shown looks like it was just from cranking the engine over with the starter.

So to start with he is going to clean the block and take some measurements and perform a magnetic particle test to see if there are any small cracks we couldn't see.

 

[Fishermark]

Sounds like a good plan. Good luck and keep us informed of the progress! :happy:

 

[ethan169]

Update:

So I finally heard back from the machine shop. It looks like the head is salvageable but the block has two small cracks in it. He did a mag particle test on both to determine this. He said he has a guy that can fix the cracks and do a good job. However hes concerned that with the cracks and the sleeves we may be putting too much work into this block. Hes also concerned that the sleeve may distort the neighboring cylinder when pressed in.

My options (I think):

- find a GM 250 block that is rebuild-able. I've found a few "complete" long blocks for around $300. The one that I found that is closer is said to be running but "smokes". Id have to check it out to get more information.

- I could look for a 4.3L V6 as bondo suggested and build it if needed and fab some front motor mounts. The mounts shouldnt be too bad to fab up.I have no idea where to find a marinized setup or what it costs.

- I could find a GM 350 pretty easy and marinize if needed. I would also need to fab mounts and figure out what needs to be done with the outdrive gears and inner transom plate. Im not even sure if a 350 would fit in the doghouse of this boat. I still have to measure it. This would be some work for sure but would be a pretty sweet little custom rocket.

What do you guys think? I think my best option is to find a good block that I can finish this build with and use all the same parts. Or replace whats not good like the manifold etc.

Any suggestions?

Here are a few pics for those who like pics...

 

[Fishermark]

All of those are viable options. The easiest would be to find another 250 straight six and drop it in after rebuilding or evaluating it. One thing to look for - not all the 250 blocks have provisions for the front mount. It can be "fixed" to work by fabbing up a mount... but if you can find a block with the extra two holes for the front mount it will be easier. Here's a couple of pics of what I ended up doing with an engine without the mount area. It worked fine.

 

[alldodge]

Go for the V6 route

 

[Scott Danforth]

I myself have a soft spot for inliners. your machine shop should have another block for about $200 plus machine work.

If it were me, I would find a 292 and build that. you should get about 250hp out of it at the crank, which is about 220 at the prop.

if your looking for a cheap motor, the 250 was installed in everything from novas to camaros to GM trucks to delivery trucks for UPS, Fed Ex, wonder bread, and frito lays. I have found low mileage 250's for the $150 range from your local you-pull-it yards

 

[ethan169]

Just a quick update....

As I mentioned earlier the first block ended up being cracked and it was already bored 0.060 over so it was scrap. I found another short block form a late 60's truck that didnt have the correct front mount but I figured I could deal with that. I dissasembled it and brought it to the machine shop to be mag particle tested. It ended up being cracked in the exact same spot! but worse...

So I kept looking and I found a guy that had three full long blocks sitting in his shed. He basically said I could have my pick from them and he would "garuntee" that which ever long block I ended up going with wouldnt be cracked. He said if the mag particle test showed it was cracked could come back and try the next one. And then the next one. If they were all cracked he would give me my money back. I was inclined to trust him, besides it wasnt like if I lost the money I would be put in the poor house.

Anyway I dissasembled the 3rd block and brought it to the machine shop. A few weeks later the machinist got a chance to wash the block and run the mag test and it checked out ok! It was standard bore and all origional too! We decided to bore this one 0.030 over. I had to buy a set of 30 over pistons to fit this since I had a set of basically never used 60 over pistons form the first engine and two sets of standard bore pistons from the two addiitonal blocks. The machine work has been done and Im getting the parts in tomorrow. I should have them at the machine shop soon and he should be almost done with the block.

Then Ill move onto the head and start assembling! I might actually have this boat in the water sometime this season! I still have a ton of other work to do on the boat though. I need to remove the center section of the floor and remove the fuel tank. Sample the stringers and transom (hopeing they dont need much work but we will see). Then replace the floor over the fuel tank. Ill need to do some rewiring and check the trim pump. go through the outdrive and change some seals and a gimbal bearing/bellows kit. Then maybe ill be good to go?

Ill report back with updates and pics when I get some parts!

 

[ethan169]

End of summer update. It was a good summer I did lots of boating and other activities but didn't really get any work done on this boat. Here hoping that I will be able to get this boat in the water for next year.

So here is where I am at now. I have started to assemble the lower end of the motor. Right now i have checked the main bearing clearances with plastiguage per the mercruiser service manual that I have for this motor. They all appear to be within spec as they should. I installed a new rear main seal the new bearings of course and installed the crankshaft. I torqued the main caps to spec (the mercruiser manual calls for 85 ft-lbs) but it seems too tight. The crank doesnt really spin that easily anymore. I can spin it by hand but it takes quite a bit of effort. This doesnt really seem right to me. Does 85 ft-lbs on the main bearing caps seems too tight? I am using permatex assembly lube by the way so its not like the bearings are dry. It just seems like 85 is alot and most other gm250 blocks call for 60-70 ft-lbs for the mains. Maybe the marine engine is torqued to a higher spec?

Any thoughts on this would be greatly appreciated! I don't want to trash a freshly machined block!

 

[alldodge]

If you prelubed the bearings, the caps are in their original positions with arrows facing forward, and your end play is within 0.002 and 0.006 max. There will be some drag from the new seal.

Was the crank reground?
Was the line bore checked?

Torque is correct

 

[Fishermark]

How tight is "too tight?" That is hard to answer on a forum like this. Sounds like you have established a good relationship with the machine shop. Have them evaluate your short block now that you have the crank installed. Now is the time to take care of any problems. You may need the main caps line bored... but maybe everything is alright. They can tell you better. Good luck!

(By "too tight" I mean the physical turning of the crank by hand, not the torque of the main caps).

 

[ethan169]

I believe the caps were line bored as they had a fresh crosshatch on them. But I'll have to look at the paper work. When I checked the clearances with the plastiguage I don't remember torquing to spec. I the manual called for 12-15 ft-lbs. Wouldnt you want them at full torque to check clearances?

I'll give the machine shop a call tomorrow and report back.

Thanks for the replys!

 

[alldodge]

I the manual called for 12-15 ft-lbs. Wouldnt you want them at full torque to check clearances?
!

Yes you want them torqued to spec (85). The 12-15 is just to seat them all before you torque. I would bet your fine, probably just the seal causing the drag.