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Judge my cylinders!

Grumpy Bear

Grumpy Bear

Regular Contributor
1974 Merc Thunderbolt 50hp. The #3 cylinder had no compression (pic 1) but the rings were stuck and scored when I opened it up. Had to dig them out. Noted a broken reed which probably caused this issue. The other cylinder (pic 2) had great compression but still stuck rings (1 of which I had to dig out of the groove). When I run my fingernails over the visible scores of the cylinders, there is just a slight feel of scratches detected that bump my fingernails. This is a 1974 motor...I don't want to spend a ton of money completely rebuilding it with cylinder sleeves, etc. Just want it to run this motor for a 3-4 years with a handful of uses each year. I'm planning to "hone" these cylinders to de-glaze them with a spring-mounted cylinder hone. Will de-glazing these cylinders be enough be enough in your opinion?

cylinder 1.JPGCylinder 2.JPG
 
Grumpy Bear said:
1974 Merc Thunderbolt 50hp. The #3 cylinder had no compression (pic 1) but the rings were stuck and scored when I opened it up. Had to dig them out. Noted a broken reed which probably caused this issue. The other cylinder (pic 2) had great compression but still stuck rings (1 of which I had to dig out of the groove). When I run my fingernails over the visible scores of the cylinders, there is just a slight feel of scratches detected that bump my fingernails. This is a 1974 motor...I don't want to spend a ton of money completely rebuilding it with cylinder sleeves, etc. Just want it to run this motor for a 3-4 years with a handful of uses each year. I'm planning to "hone" these cylinders to de-glaze them with a spring-mounted cylinder hone. Will de-glazing these cylinders be enough be enough in your opinion?

View attachment 11192View attachment 11193
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I've been down this road (many times), and sometimes, a quick clean-up with a brake cylinder hone will do the job. At worst, you will be no further behind if it doesn't. A couple of suggestions:
1. CLEAN! before starting, clean the jugs with muriatic acid, this will remove any oxides left by embedded aluminium. Just because you can't see or feel it, doesn't mean it's not there. After the acid clean, use lots of water to remove any traces.
2. Select the correct hone and stones. The stones need to be long enough so they will not catch in the ports, and turn your block into pop cans. #320 grit stones should smooth out the striations.
3. Get her plenty wet! Use lots & lots (&lots) of cutting fluid, and best to hone downward, so the cuttings will run out the spark plug boss. Keep your hone speed low, and try to create a 30-45 degree cross-hatch. Use the same number of strokes on each jug, until you reach the desired level of finish.
 
(1) Mike the cylinders if more than .003 out it needs bored (2) Mike around the intake/exhaust port as this is where inline motors wear (3) Do not use a spring hone as it follow imperfections in cylinder use only a rigid hone. (4) Worn cylinders will cause idle problems and dying when put in gear..It is very rare to find cylinders still within spec on a inline that has had normal use. When you run a rigid hone down cylinders it will show wear around ports a it will not contact cylinder wall and leave a dark spot. When you re-ring and hone them without checking spec's the motors will run but problems will reappear within a year or so....
 
fastjeff said:
Agreed. Saved a bunch that were that bad.

Could you post a photo of that bad reed?

Jeff
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Sure thing. Pic is a tad blurry where the reed is broken off, but you can see it. Checked to make sure the reed stop was at the right gap and it was spot on.

reed.jpg
 
bilge rat jim said:
I've been down this road (many times), and sometimes, a quick clean-up with a brake cylinder hone will do the job. At worst, you will be no further behind if it doesn't. A couple of suggestions:
1. CLEAN! before starting, clean the jugs with muriatic acid, this will remove any oxides left by embedded aluminium. Just because you can't see or feel it, doesn't mean it's not there. After the acid clean, use lots of water to remove any traces.
2. Select the correct hone and stones. The stones need to be long enough so they will not catch in the ports, and turn your block into pop cans. #320 grit stones should smooth out the striations.
3. Get her plenty wet! Use lots & lots (&lots) of cutting fluid, and best to hone downward, so the cuttings will run out the spark plug boss. Keep your hone speed low, and try to create a 30-45 degree cross-hatch. Use the same number of strokes on each jug, until you reach the desired level of finish.
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Great advice. Thanks! Someone else said not to use a spring-mounted hone, but that's basically what I have available. Hope that will be okay.
 
kimcrwbr1 said:
You will need to go through all the bearing as well especially from the bad reed and down. Mic out the crank I wouldnt spend alot of time until you look close at everything. You dont want to put together a engine that needs rebuilt before you even start it?
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Thanks for your words. The crank is in great shape otherwise. I replaced the upper and lower bearings and seals with new ones. I replaced 2 of the pistons (the other two looked just fine) and all the rings on all the pistons. I don't have a mic, don't know anyone I could borrow one from, and wouldn't purchase one for a one-time use, so I doubt I'll be taking any of those measurements. Taking my chances, I suppose.
 
kimcrwbr1 said:
Just buy a cheap set of calipers is all I use you will be amazed how many things you will mearure when you have a set.
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I bet you're right on that one! I'll have to check and see what the cylinders are supposed to measure. Shouldn't be more than .003 off spec? Is that right? Should they also be the same width from top to bottom?
 
kimcrwbr1 said:
Not much you can do with a caliper as far as measuring the cylinders you would need a pullover guage to check inside diameter in the bore. I was more referring to crank journals for the main bearings and connecting rods
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Ah, my mistake. I was thinking about the "inner caliper" but I suppose that wouldn't be accurate/sensitive enough anyway.
 
faztbullet said:
I guess my posts of do it right or don't do it at all falls on deaf ears.....do as you want.
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??? Well, this is a forum. I asked for advice and several people provided theirs, including you. I read what you wrote and I appreciate you chiming in. There's no need, however, in getting upset if I decided not to do exactly as you suggested.
 
Not upset at all, just hate to see someone waste their money and time on a project and end up with unfavorable results later. My motto is if your going to do it , do it once and do it right despite some questionable advice.....
 
faztbullet said:
Not upset at all, just hate to see someone waste their money and time on a project and end up with unfavorable results later. My motto is if your going to do it , do it once and do it right despite some questionable advice.....
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I certainly understand that philosophy, and I try to follow it myself when circumstances allow. In this case, I could end up spending more money than the motor's worth to get everything done according to factory standards. The fact is, I'm trying to do enough within reasonable financial constraints to get this thing running for a few years (probably only putting 10 or so hours on it a year). I only said that to you before because you are the only person I've encountered on here so far who seemed to become irritated when I didn't follow all your advice.
 
kimcrwbr1 said:
Make sure you give the engine a good break in period. Mix the fuel at 40:1 and run it for at least 8 hours at variable speeds up to 3/4 throttle. You can go WOT for short spurts. Hopefully you have a good cross hatch on the cylinders to seat the rings properly. The break in period can make or break any ring job. Speed and feed it can be a challenge to get a 45 degree cross hatch consistent with a drill!
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Thanks again. My drill is variable speed, so I'll have to experiment a little to get the right vertical and rotating speed combination.
 
Sounds like you are planning on using a hand drill, if you can use a drill press, takes 75% of the error out of the job. With a drill press you can pre-set the speed and depth, then simply time the sweep.

If you use a spring loaded hone be real careful at the bottom where it can catch and be prepared to destroy a hone or two. Typically it is not gong to do any damage to the cylinder if you react quickly, but it's going to twist the hell out of the hone.

I've never tried to actually bore anything but have deglazed and to some extent honed snowmobile jugs, with 50/50 success. One issue to overcome is if you actually take much material off you must chamfer the ports - this is absolutely necessary otherwise you very likely risk catching/breaking a ring.

The tools to chamfer are easy to come by - something as simple as a dremel with the right bit will do it (I think machine shops use an air tool but similarly just by hand), however actually being able to do it well and/or know it's done well is the hard part that takes practice and experience.

Jon
 
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