Broken Piston

[meadowbrook]

Hi.

Long time no post.

lookinh for tips on a quick way to fix this issue. 

My 50 Meadowbrook's original engine broke a chunk off #4 piston , which caused a loss of compression and a rattling sound. 

Otherwise the engine ran fine, go figure.

Pulled the head and was surprised to see no damage to the cylinder wall. I guess aluminum is way softer than steel. 

Anyway, it's the same for all other 5 cylinders, no wall damage. 

My oil pressure has always been excellent, about 45 pounds hot at anything above idle. 

I was thinking of dropping the pan, removing the rods and pistons, honing and replacing with new pistons, rings and rod bearings.

 

Is there a Wayne to hone and covering the bottom of the cylinder to keep crap from the crank?

 

I saw an old shop manual that showed a vacuum hone setup to suck out the particles. 

 

A readon son I don't want to do the whole engine aside from cost is project creep. If I rebuild, then I'll paint the engine then I'll have to re paint the engine bay and the the car. It's a survivor so I'd like to avoid that. It has 85000 miles. 

[Plymouthy Adams]

short rebuilds were the norm many years ago and I seen one done every Thursday for a long time at the station I worked at.  These two men would take the engine down, send off the heads to the local machine shop, actually they picked up and delivered...cut the cylinder ridge, remove the slugs, mic' the bore..check the taper and if within tolerance proceed with the re-ring, new inserts, new oil pump, timing gear set etc. etc. get the heads back in about 4 hours, they were finished with their work by then awaiting the heads and pop them on, new tune up on assembly and back to the owner.  Yes to the surprise of many a re-ring while a low end budget fix and not as long lived as that of a complete bore and new slugs will breath new life into the engine for a few more years of daily driving and with one that is driven way less distance annually, well odds are you can come out way ahead. All of these were either SBC or Fords engines.  I on the other hand though some of these engines would have done just as well with a valve job but they would sell the short overhaul packages.

[Sharps40]

Pull no 4 and pan 

 

Cover crank at 4.

 

Tape off 1 2 3 5 6 cyls

 

Measure and lightly hone cyl 4 [optional if unscarred and not badly tapered]

 

Clean it all twice. 

 

Fit new piston and rings

 

Reassemble and break in 20 mins at 2000 rpm. 

 

Go drive

 

 

 

 

 

[Los_Control]

Going to agree with PA on this one, this was the norm and done at your local gas station.

My father was a mechanic that did these jobs and worked at a local gas station.

Which is why our cars were always shiny, but broke down often   .... cobbler kids have no shoes  

 

Same time, 80k miles is nothing to our modern cars, for these older cars it is time for new rings and bearings anyways. 100k is very good to get.

I think I would want to do all the rings and bearings while in there, assuming all the cyl and crank check out to specs.

Maybe just start with #4 and see if it meets specs, then proceed with caution from there.

[Veemoney]

3 hours ago, meadowbrook said:

I was thinking of dropping the pan, removing the rods and pistons, honing and replacing with new pistons, rings and rod bearings.

 

3 hours ago, meadowbrook said:

Is there a Wayne to hone and covering the bottom of the cylinder to keep crap from the crank?

 

Meadowbrook,

For your approach to keep crap off the crank

• I would do most work like initial measurements for size and taper,  removing any ridge at the top of the cylinders and then vacuum the cylinders.
• Pull piston rod caps and move the pistons up toward the top of the bores but do not remove till the next step is complete.
• I would use some rags like old t-shirts &r plastic garbage bags to drape over and wrap the crank to deflect or capture contaminants before pulling the pistons all the way out.
• Once you pull the pistons confirm measurements and touch up cylinders as needed. I like to use a ball hone at a minimum to scratch/deglaze the cylinder walls. It doesn't take much and will help the new rings seat.
• Once you have the cylinder prep complete & have cleaned  the cylinders vacuum the lower areas around the crank to remove anything on the rags below.
• During the repair & cleaning refrain from using air to blow off the areas as this can move contaminates to other areas of the engine.
• Also since you have the head off you could have it milled to give you a little more compression if it has not been done previously to the max. Don has posted the head milling info and process for measuring and head milling is the best bang for the buck in my opinion if you have the head off.

Hope this helps  

Edited July 10, 2019 by Veemoney
add detail

[greg g]

Well back in the day, lots folks would only repair the one piston involved, botton it back up and keep on Motoring.

[DJ194950]

26 minutes ago, greg g said:

Well back in the day, lots folks would only repair the one piston involved, botton it back up and keep on Motoring.

 

I may do that if the cylinder wear is such that a rebuild was really almost - depending upon what the compression readings in the other 5 cylinders are.

Even if they were 70+ psi and somewhat even I think one set of rings and a piston after a ridge removal and honing, put back together and drive and drive AND.....

 

dj

• Quote

[Reg Evans]

Yeah, back in the day....In my case last year.  #1 cylinder started loosing compression so I removed the head and discovered the problem.  The cylinder and the piston were scored for some damn reason.  I'm guessing I got a piece of wire in that cylinder when I was wire brushing the tops of the pistons and valves the previous year when I installed the engine.  Anyway...I found a box of 6 pistons with wrist pins and rings 60 over like my engine is on eBay for cheap. I removed #1 Piston and honed out that cylinder and installed the new piston.  So far so good.

[DJ194950]

When a engine is already +60 it is about the end of it's life, but I can get +70 new American made pistons (not cheap though) and even new +40 rod bearings ($30 per set, last I checked) so don't write mopar flat motors off too easily.

 

Complete rebuilds are Expensive these days it seems,  so run them as long as you are not doing major damage by continuing to use them.

 

Glad yours is still alive Reg,.

 

Keep them working, sitting often does more damage than use.

 

dj

[DJ194950]

Looks the rod on the damaged piston may have been  the source of your problem????

Edited July 10, 2019 by DJ194950

[dpollo]

In car overhauls were commonplace back in the day and even if the cylinders were a little beyond specs, good results could be obtained which might extend the engine's service life another 20 000 miles or more.

[westaus29]

I had a top break off a piston in my 29 Plymouth 4 cyl flathead at 54 mph back in the days when 3 kids were at college and funds were low. Stopped and had it towed home. Similar story, a bit of a rattle and no damage to the bore, so found an oversize second hand piston, had it machined to fit , honed the bore with crank covered then gave the crank a good wash with kerosine in a squirt bottle and put it all together and took it quietly for a while. did quite a few thousand miles with no issues. As stated by others above, part rebuilds were common in the old days. Of course if you plan to drive it hard, you need a total rebuild!

[Matt Wilson]

All good replies.  The only thing I still wonder about is how to deal with the ridge at the top.  The last time I removed the ridges from the tops of the cylinders, I thought I was being very careful not to remove more than necessary to get the pistons out, but my machinist said I removed a bit too much - enough that he had to bore the cylinders out by two oversizes instead of just one oversize (He had to go to 0.030" I stead of 0.020").  I'm thinking if you don't remove enough of the ridge, you can beat the piston out of the engine (something my machinist said he recommends), but do you run the risk of the new top ring hitting the remainimg ridge? If you remove too much of the ridge, is there any issue with that, such as the top ring comtactimg the "de-ridged" area?  Maybe I'm over thinking this. 

[Dave72dt]

If you are re ringing only, you want the ridge gone.  If you're going to bore it, then leave a little.  It won't matter if you damage rings or pistons.  Beating them out with ridge remaining can sometimes break ring lands on the piston.  New rings on the same piston won't travel any further in the bore than the old ones did.  The difference is the new rings will have sharp edges and probably fit in the ring grooves tighter so the possibility of them coming up against the bottom of  left over ridge and breaking new rings or ring lands on the piston exists.  Most machinists will automatically bore to .030 over for a first time bore.  Almost every engine will clean up at that size if it's salvageable.  While many will clean at .020, you may find one cylinder that doesn't and you don't want a mismatched set if possible.  Yes, it's been done as has grinding a rod bearing down an additional size.  For assembly ease, don't mix and match.