Replacing a piston in 3 and 4 cylinder engines.

[Spinkick]

Re: Replacing a piston in 3 and 4 cylinder engines.

Got the reed gaskets, intake gaskets, carb gaskets and needle installed. No leftover parts too!

Today I'll be rebuilding the fuel pump and replacing the inline fuel filter with a new one.

Question: Since only one piston has been replaced, do I follow the same 10 hour break-in method as I did when the motor was completely rebuilt?

Hoping to put it on the water tomorrow. Thanks for all your help.

 

[Frank Acampora]

Re: Replacing a piston in 3 and 4 cylinder engines.

YES! Each cylinder is completely separate and acts like a complete engine so the piston you replaced still needs a break-in period.

 

[Spinkick]

Re: Replacing a piston in 3 and 4 cylinder engines.

Well, I couldn't start the motor because the battery was too low, so it has to wait until morning.

When I did the carb gaskets I noticed the carburetor, overall was quite clean. The main jet had just a *little* buildup on it, but I doubt it had much, if any, effect.

However, I do recall above somewhere you mentioning a weak fuel pump could have contributed to the lean cylinder.

This is what I found when I took it apart...

Does that look weak enough to be the source of my problem?

 

[Frank Acampora]

Re: Replacing a piston in 3 and 4 cylinder engines.

One can not tell from looking at photos. The only way to check, aside from obvious damage, is to check output pressure. An adequate fuel pump will put out -- if I remember correctly -- about 2 PSI at idle and up to 6 PSI at full throttle.

I do not see any obvious damage in the photos unless the black line in the lower right quadrant of the second photo is a cracked diaphragm.

 

[Spinkick]

Re: Replacing a piston in 3 and 4 cylinder engines.

nothing was broken or cracked. The diaphrams were quite stretched, though. Also the two discs (can't recall the names) had a pretty good bowl shape to them as you can see in the picture.

 

[Spinkick]

Re: Replacing a piston in 3 and 4 cylinder engines.

CASE CLOSED!
I did have to go full throttle very briefly a couple of times the first hour. What a difference!!! The fuel pump was apparently the centerpiece of the performance problem I had because it ran like a scalded dog!

Thanks for all your help Frank.

 

[Imgonefishing]

Re: Replacing a piston in 3 and 4 cylinder engines.

Bumping this up top because I spent hours trying to find this post that I knew was there from reading it last year.

 

[Bigprairie1]

Re: Replacing a piston in 3 and 4 cylinder engines.

Quick bump on this excellent thread from Frank.
After taking a year off from boating to do several other hobbies I am finally going to start in on replacing the (centre) piston from my '90/90hp that I had go south on me last year. So hopefully I will have this work done before I button up the boat for winter ready for next season.
I might have a few questions for you Frank (and JerryJerry) regarding this...so hopefully I can get you guys on board with some information and hopefully some recommendations and assistance.
One thing that wasn't clear in the first post was attacking the piston removal from just 1 carb...did I understand that correctly? I was thinking of taking the whole 3 carb/manifold set up off as 1 complete unit. Then try to get at the connecting rod bolts from there?
....or am I making a mistake in thinking this?
All Good
BP

 

[Frank Acampora]

Re: Replacing a piston in 3 and 4 cylinder engines.

Tou must remove all three carbs to access the manifold bolts and you must remove the manifold and reeds to access the big end of the rod.

 

[Bigprairie1]

Re: Replacing a piston in 3 and 4 cylinder engines.

Tou must remove all three carbs to access the manifold bolts and you must remove the manifold and reeds to access the big end of the rod.

I'm hoping to cover some groung on this today Frank. At a glance, it looked (originally) that the 3 carbs could be removed with the manifold intact as 1 complete intake unit?.....am I wrong on this?
I'm hoping to leave as much undisturbed on the entire set up as possible...it was running great apart from that ring grabbing and breaking that centre piston.
Quick questions: while I'm at it....should I look at doing all 3 pistons?...or at least pulling the other two and giving them a good decarbon soak?
Is it tricky to not drop those roller bearings when you undo the connecting rod cap(s)?......are there some good tricks for this in order to retain everything and get it out of that tight space intact and ready for some re-use?
Again, many thanks on this guys I really appreciate it.
BP

 

[Bigprairie1]

Re: Replacing a piston in 3 and 4 cylinder engines.

Frank, if you are in today I have a question on the Wiseco pistons and some clearance checking:
Backstory: I am getting ready to do my final re-assembly of my centre piston/rod on the 3 cylinder/90hp Force and I am using a new (single) Wiseco piston.
Parts on hand are as follows:
-Wiseco Piston 3151P3 (.030" over)
-Wiseco Ring set 3405KD
-Bearing/spacer kit W5216
I will be re-using the original rod and have successfully disassembled it from the original damaged piston (non-wiseco).
The new Wiseco rings appear identical and both are marked 'top'. (is this correct so far?)
The Force manual says that the top ring clearance should be .010" to .020" and the bottom ring clearance should be .006" to .016"....this appears to be applicable to the 1989C-1995 which I'm pretty sure mine is.
So....how can what appears to be 2 identical (new Wiseco) pistons rings have 2 different gap/clearances within the same piston bore?
OR...are these above Force clearances just for the original style ring kits?
Note: I measured about .020" when I 'check' installed these new rings in the piston bore....needless to say both rings presented the same clearance.
So far so good, any input on this would be great Frank and/or any other tips at this point?
Many Thanks
BP

 

[Frank Acampora]

Re: Replacing a piston in 3 and 4 cylinder engines.

Top and bottom rings are identical in Wiseco pistons. Force specs call for different clearances because the top ring runs just a little hotter and therefore expands slightly more. However, if the top ring is within factory manual clearance and the bottom is at the same clearance, no harm will be done and really, you won't see any loss in compression.

You did not get two top rings. Both rings are labeled "Top" because the rings have a 2 degree taper on the top edge. It is difficult to see yet important to install them with the top up so the flat side sits on the bottom of the ring groove. Thus, the top of the ring is marked.

You can bet that any reputable manufacturer of pistons and rings has a really good quality control program. I would be willing to bet that (for example) rings are controlled to a tolerance of ten thousands of an inch .0001-.0010. SO: How can two essentially identical rings have a different gap in the same bore? If ring clearance is too tight (due to poor machine shop quality control) standard practice is to file the open ends until the installed ring has the correct gap. Thus: manually, you can set the gap.

In your case, simply install and forget. You won't have any compression problems.

 

[Bigprairie1]

Re: Replacing a piston in 3 and 4 cylinder engines.

Top and bottom rings are identical in Wiseco pistons. Force specs call for different clearances because the top ring runs just a little hotter and therefore expands slightly more. However, if the top ring is within factory manual clearance and the bottom is at the same clearance, no harm will be done and really, you won't see any loss in compression.

You did not get two top rings. Both rings are labeled "Top" because the rings have a 2 degree taper on the top edge. It is difficult to see yet important to install them with the top up so the flat side sits on the bottom of the ring groove. Thus, the top of the ring is marked.

You can bet that any reputable manufacturer of pistons and rings has a really good quality control program. I would be willing to bet that (for example) rings are controlled to a tolerance of ten thousands of an inch .0001-.0010. SO: How can two essentially identical rings have a different gap in the same bore? If ring clearance is too tight (due to poor machine shop quality control) standard practice is to file the open ends until the installed ring has the correct gap. Thus: manually, you can set the gap.

In your case, simply install and forget. You won't have any compression problems.

Thanks Frank...that gives some positive info in heading into the (hopefully) final stretch. The last major thing to do here prior to the piston installation is that port chamfering stuff. I don't have a useable dremel at this point and the motor is still mounted on the boat in the yard so basically I'm going to attempt to do it with a small file and try to keep track of anything that files off/and out....maybe give the shopvac a really good 20 minutes work out in there. Jiggs had some great info around this too so I'll give it my best shot.
Then I'll do a final hone and go for the piston install.
all good
BP

 

[Jiggz]

Re: Replacing a piston in 3 and 4 cylinder engines.

Thanks Frank...that gives some positive info in heading into the (hopefully) final stretch. The last major thing to do here prior to the piston installation is that port chamfering stuff. I don't have a useable dremel at this point and the motor is still mounted on the boat in the yard so basically I'm going to attempt to do it with a small file and try to keep track of anything that files off/and out....maybe give the shopvac a really good 20 minutes work out in there. Jiggs had some great info around this too so I'll give it my best shot.
Then I'll do a final hone and go for the piston install.
all good
BP

Others recommend a mini-dremel or short dremel to do the chamfering but in my case because I have big hands that barely fits the cyl I cannot get my knuckles in while holding the dremel. So I used a regular long dremel tool from Harbor Freight for less than $15. With this tool you do not need to get your hand inside the cyl to do the grinding. Or maybe if you already have a dremel, use the flexible extension instead.

 

[Nick 7933]

Re: Replacing a piston in 3 and 4 cylinder engines.

This post is awesome, great information here.

I'm looking for some advice, I'm a brand new boat owner, picked up a 1989 bayliner capri 19' with the force 125 motor on it. I literally just picked this boat up a couple of weeks ago. with a young family, I thought it may be a summer activity we could all enjoy.

Anyway, I just took the boat out yesterday, it ran pretty smooth, a little rough for the first minute or two, but it's been sitting since last summer and it cleaned out after less then a minute. I did notice that it seemed underpowered and a little doggy, though the motor didn't seem to skip or run rough, I could tell it wasn't reving up as I would have expected. I thought maybe the carbs needed to be cleaned.

I pulled it into the garage tonight and figured I would clean the carbs - but I decided to check the compression first since it's so easy with the plugs right there. the top cylinder was 0, cylinder 2 was 100-110, the bottom 2 cylinders were 150. I double checked the top cylinder a couple times, and I even tried spraying in some oil and rechecking, still 0. I also noticed oil coming out of the top carb...

I'm guessing the rings, maybe a hole in the piston though I looked in with a flashlight and couldn't see anything obvious. I've rebuilt my fair share of snowmobile and ATV motors, it's been a while for sure, but I've never seen a compression test come back as 0!!! has anyone seen this scenario? anything else I should look for? I'm going to rip the head off tomorrow and take a look, I'll probably follow the info in this thread and pull out the top 2 pistons (bottom 2 seem fine). I'll check to see if they are oversized and order some wiseco pistons - I've had good luck with them from ATV's

thanks for any feedback you all may have

 

[Nick 7933]

Re: Replacing a piston in 3 and 4 cylinder engines.

This post is awesome, great information here.

I'm looking for some advice, I'm a brand new boat owner, picked up a 1989 bayliner capri 19' with the force 125 motor on it. I literally just picked this boat up a couple of weeks ago. with a young family, I thought it may be a summer activity we could all enjoy.

Anyway, I just took the boat out yesterday, it ran pretty smooth, a little rough for the first minute or two, but it's been sitting since last summer and it cleaned out after less then a minute. I did notice that it seemed underpowered and a little doggy, though the motor didn't seem to skip or run rough, I could tell it wasn't reving up as I would have expected. I thought maybe the carbs needed to be cleaned.

I pulled it into the garage tonight and figured I would clean the carbs - but I decided to check the compression first since it's so easy with the plugs right there. the top cylinder was 0, cylinder 2 was 100-110, the bottom 2 cylinders were 150. I double checked the top cylinder a couple times, and I even tried spraying in some oil and rechecking, still 0. I also noticed oil coming out of the top carb...

I'm guessing the rings, maybe a hole in the piston though I looked in with a flashlight and couldn't see anything obvious. I've rebuilt my fair share of snowmobile and ATV motors, it's been a while for sure, but I've never seen a compression test come back as 0!!! has anyone seen this scenario? anything else I should look for? I'm going to rip the head off tomorrow and take a look, I'll probably follow the info in this thread and pull out the top 2 pistons (bottom 2 seem fine). I'll check to see if they are oversized and order some wiseco pistons - I've had good luck with them from ATV's

thanks for any feedback you all may have

Well I pulled the head off tonight and found the top piston had a hole in the side. the second piston looks like it started to eat the ring a little bit too. guess I'll be going with 2 wiseco piston kits. the bottom 2 look great, the cylinder walls even look as though they still have crosshatching on them from the honing of a previous rebuild.

only question I have now. on the top of the pistons there is a "2" I'm not sure if this is significant not, in my experience with ATV's oversized bores are usually signified by a 0.02 or something like that - does anyone know what the 2 signifies? I can try to measure the cylinder I suppose.

 

[Bigprairie1]

Re: Replacing a piston in 3 and 4 cylinder engines.

Ok, I find myself needing some help guys....and this thread is still so useful and valid, I have attempted to extend it further.
Quick backstory on the piston replacement delay....a lot of other priorities (family, etc, etc) have gotten in my way of getting this piston replacement completed from last fall but I 'hope' I'm on the final stretch and maybe might have the motor running by the end of the week.
However, I'm having some issues and I have a few questions if anyone can help me out?
What is the best way to install the (2) bearing cages and the little roller bearings in this process?
ie: I tried by setting them into the rod saddle as I inserted the piston and they slowly moved down just enough to cause interference with the crank journal...hmmm. :facepalm:
Should I assembly 1/2 of the cage/bearings and install them through the reed opening then slide them around the crank journal 180?? the push the rod/piston assembly into place onto them from there?
Also, any tips on how to get the rod aligned with the crank journal generally? (the rod floats on the piston pin and naturally under its weight biases itself out of alignmen with the crank journal during replacement).
I have been using a couple of long makeshift rods to reach in through the reed port and try to slide/centre the rod up to align with the crank journal....but not too successful yet...and definitely not successful when the bearing cage slides down under its weight while I'm putzing the rod up to centre.
Note: I'm using some reasonable viscosity assembly grease to hold the bearing cage and bearings in place but it isn't a 100% system particularly with the minor assembly vibrations during re-assembly.:blue:
Ok guys (and hopefully Frank), I'll leave off there for a minute.
Any advice on this would massively appreciated.
All Good
BP

 

[Bigprairie1]

Re: Replacing a piston in 3 and 4 cylinder engines.

...bit of an update and a quick incidence of 'what was I thinking' I guess.
I pulled the (new) piston/rod assembly back out and simply put the pre-assembled bearing cage and rollers in from the open cylinder side and right onto the crank journal with a large needle nose plier...no problem. (again...what was I thinking LOL:facepalm
After that, I simply re-inserted the piston/rod assembly and with a little jiggling and maneuvring was able to get the rod up aligned with the crank journal and seated onto the (previously installed) bearing cage...or at least the inner 180? half.
After that the outer rod cap and its bearing cage (and bearings) weren't too bad.
However, after snugging up the (2) 1/4" 12pt. bolts I realized that.......what...my torque wrench goes from the 25 lb-ft and up range.....and the assembly manual calls up a 170 in.lb requirement (14.2 lb.ft)... LOL. So for the day, I might be dead in the water, or out of the water as the case might be.
I would post the pics of the assembly process so far, but they are larger than what the site allows.
Quick assembly info so far: I was careful to ensure the rod cap went on the right way because as Frank mentioned..there is a wrong way. After that I carefully inspected the slightly tightened assembly to ensure that the rod cap was indeed tight to the main rod join point and that there were not any rogue/missing bearings laying around in there.
So far so good, I think.
.....now time to go find a smaller torque wrench!!
More to come.
BP
Note: without that small torque wrench.....is there anything wrong with putting the head assembly back on?...or is this best to leave it for last?

 

[jerryjerry05]

Re: Replacing a piston in 3 and 4 cylinder engines.

When putting in bearings, you need to lube them.
They sell a product called: Bearing Assembly Grease.
ANYTHING else??? You can run the risk of burning the bearings.
The regular grease won't dissolve like the B.A.G.
If you can get them together with out anything,great. But use tranny fluid on the bearing and rings.
You can use regular oil too.
Doing anything through the reed plate opening is a B.
The main bearing under the stator needs to be locktited in place.

 

[Bigprairie1]

Re: Replacing a piston in 3 and 4 cylinder engines.

When putting in bearings, you need to lube them.
They sell a product called: Bearing Assembly Grease.
ANYTHING else??? You can run the risk of burning the bearings.
The regular grease won't dissolve like the B.A.G.
If you can get them together with out anything,great. But use tranny fluid on the bearing and rings.
You can use regular oil too.
Doing anything through the reed plate opening is a B.
The main bearing under the stator needs to be locktited in place.

Yep, got it.....the grease I used was heavier bearing grease. As well, I had some general engine assembly lube in there too.
As for the torque wrench....got that solved as well. Being Father's day I got a great discount on a new quality lower range torque wrench for 60% off....rockin'!!
Snugged up and torqued the rod bolts already, chased out the head threaded taps...so almost ready for the re-assembly.
Here is a new question based on an odd assembly system:
The head on my 90/91 Force 90hp is a 2 piece unit with the outer component being the fairly flat (not 100%)/simple plate with the cooling fins on it. It sandwiches the larger/main combustion chamber head plate to the block with the head bolts going through the 2 of these plates and into the block.
Now, I have not seen any reference to any extra gasket outer for this...even when I ordered my head gasket, it wasn't in the set...hmmm??? (is there an outer gasket for this?...just make one? or?)
When I removed it originally, it was simply siliconed to the other one....Is this correct???
If so, doesn't the use of silicone as a layer affect the torque values??
Any ideas, info or feedback on this odd set up would be greatly appreciated!!!
Also, quick second question: Does it matter if you install the cylinder head plates before the intake side during re-assembly? (6 of one....1/2 dozen of the other?....just checkin?)
Many Thanks in advance guys!!
BP