1978 Mercury 80HP rebuild Spec ??

[Zrt1200]

Hi guys, I just tore my 80HP in-line 4 apart for rebuilding. I also just ordered a factory manual but it will be a week before I get it. Does any one have the bore specs?? Tolerance?? Out of round?? Thanks guys. Zrt

 

[Zrt1200]

Re: 1978 Mercury 80HP rebuild Spec ??

I went to the dealer today to get bore specs. The out of round and oversize limit is .003-.004 My bore is +.0015 to +.002 So I will hone it and check again after the hone job. I also took the rings off to check ring end gap. Wow are these rings shot. Ring end gap was over .063 So after the hone job I will see what the ring end gap is supposed to be.

 

[Laddies]

Re: 1978 Mercury 80HP rebuild Spec ??

 

[Zrt1200]

Re: 1978 Mercury 80HP rebuild Spec ??

Laddies Supreme Mariner. Thank you very much!! Now I just need to get the ring end gap specs.

 

[Laddies]

Re: 1978 Mercury 80HP rebuild Spec ??

Because the rings are pinned they are usually prefit and only need to be slipped in the bore before assm. to make sure they are the correct ring for what ever the engine bore is a not a oversize ring.

 

[Zrt1200]

Re: 1978 Mercury 80HP rebuild Spec ??

I just got thru checking my crankshaft. The rod journals are as follow

#1 = 1.1386

#2 = 1.1384

#3 = 1.1385

#4 = 1.1386

Spec say's 1.139 (Is there a + or - to these specs)??

Center bearing (upper is 1.2376) and (lower is 1.2377) Spec calls for 1.238

Mag and Pto ends were the same at 1.1802

 

[Laddies]

Re: 1978 Mercury 80HP rebuild Spec ??

That should be fine we polish more than that off racing cranks to loosen them up a little.

 

[Zrt1200]

Re: 1978 Mercury 80HP rebuild Spec ??

Thank you, That ease's the mind on the crankshaft rod journals anyways.Now for the next question. I just checked the pistons and the skirt side on all 4 pistons was between 2.864 to 2.865 According to the chart which is for a older year Mercury 80HP that is fine but according to the newer (1976)85HP that is way sloppy. According to mercury parts on-line they both have superseded to the same part number. So I am confused on this one?? The top of all 4 piston's was between 2.856 to 2.857. I will try to load some pic's later. Thank You!!!

 

[Laddies]

Re: 1978 Mercury 80HP rebuild Spec ??

Pistons for a 78 or between 4831999 and 6432900 use the 2.875 part # 745-6664A# piston which the skirt dia. should be 2.872 and 2.863 above the rings. Sorry I didn't notice the specs. for your pistons were not on that chart.

 

[Zrt1200]

Re: 1978 Mercury 80HP rebuild Spec ??

Thank you, That tells me my pistons are shot. skirt Dia. = 2.865 and top above the rings = 2.857

 

[Zrt1200]

Re: 1978 Mercury 80HP rebuild Spec ??

Sense this motor was built in 1978 when we still had leaded fuel I was wondering if I would be better off with low dome pistons over the high dome?? I really do not want to loose any power though. What are your guys thoughts on this??

 

[Zrt1200]

Re: 1978 Mercury 80HP rebuild Spec ??

This Pic is a little small.

 

[Laddies]

Re: 1978 Mercury 80HP rebuild Spec ??

Just a couple of things, first make sure the cyl. taper and out of round are within specs, after running a precision hone in the bores don,t try to cheat as those engines a very picky about it and you only need to buy one set of pistons if you may need to rebore, do it now. A thought if the bores are true but loose some time a forged piston will save a rebore as they need extra clearance. Your engine came with high dome if thats the right name for them thats what you must run. If worried about fuel retard the timing a few degrees. Always look up your parts at a Mercury site and if you want to run parts of other manufacture cross the numbers to there number. Here's a good site for parts look up go there with your serial number and check you part numbers.
http://www.mercruiserparts.com/selectSerailRange.asp?doc_nbr=800+(4+CYL.),+80+(4+CYL.)

 

[Zrt1200]

Re: 1978 Mercury 80HP rebuild Spec ??

Thank you for the reply. Just so you know I am not trying to be cheap in any way when it comes to this motor. I am planning on buying bearings, seals, pistons, carb rebuild kits, a gasket set and a new water pump!!! If there is some thing else I need to buy I am going to buy it. I was just wondering if the low domes would be a better choice than the high domes with our current gasoline. It is nice to know that this is a tight tolerance motor. Some motors are not!! Thanks again.

 

[Faztbullet]

Re: 1978 Mercury 80HP rebuild Spec ??

Go ahead and bore it .020 over as cylinders are going to be worn in the port areas,use the high dome pistons as suggested,up main jets in carb .002. Check the labyrinth groves in reed blocks and if worn down(edges not sharp) or brassy in color replace them as idle and takeoff will suffer. Check restrictor passages and if missing replace or modify.

 

[bryanwess2000]

Re: 1978 Mercury 80HP rebuild Spec ??

Subscribing to thread . If you don't mind would you keep up with your costs
so the rest of us can get an idea what we would be looking at price wise to
do a similar rebuild. I have an 1977 85hp that i'm contemplating rebuilding
when it finally lets go.

 

[Zrt1200]

Re: 1978 Mercury 80HP rebuild Spec ??

Ok Pro's. I need your opinion here!! I just cleaned the rods up and checked for flatness and out of roundness. They were all flat with in .0003
Here's the dimensions of the small ends. These were checked up and down (big end to small end) and then across!! (Spec is .957)
Rod #1 .9576 & .9578 = .0002
Rod #2 .9577 & .9577 = .0000
Rod #3 .9577 & .9577 = .0000
Rod #4 .9574 & .9574 = .0000

(Now Here's were I need your opinion)!!
These were checked up and down(Big end to small end), Across the two half's and diagonally.
Here's the dimensions of the Big ends. (Spec is 1.453)
Rod #1 1.4536, 1.4536, & 1.4537 =.0001
Rod #2 1.4532, 1.4531, & 1.4532 =.0001
Rod #3 1.4531, 1.4540, & 1.4534 =.0009
Rod #4 1.4535, 1.4538, & 1.4545 =.0010

I would assume I need to replace the bottom two rods?? Thank guys!!

 

[Zrt1200]

Re: 1978 Mercury 80HP rebuild Spec ??

Subscribing to thread . If you don't mind would you keep up with your costs
so the rest of us can get an idea what we would be looking at price wise to
do a similar rebuild. I have an 1977 85hp that i'm contemplating rebuilding
when it finally lets go.

Don't wait till it lets go as some parts are not available!!!
And a note!! My Manual has still not arrived!! ERRR!!!!!

 

[Faztbullet]

Re: 1978 Mercury 80HP rebuild Spec ??

I would loosen the last 2 rods up and clean mating surfaces,torque to spec and remeasure. If still out discard and replace.

 

[Zrt1200]

Re: 1978 Mercury 80HP rebuild Spec ??

Faztbullet, You are dead on with the bore job as I Honed the cylinders today with my sunnen AN-112 hone. The bad spots were the transfer ports and right at the top of the cylinders. I honed them to +.005 and none of the 4 cylinders cleaned up 100% so it is getting a bore job!! I have not yet rechecked the rods but will try to do so tomorrow.