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Oilhead head gasket replacement - minor scratches on surface from cleanup


Christo

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In replacing weeping head gaskets on a 95 BMW R1100RS, I carefully tried to remove hard carbon deposits on each piston, using plastic and wood implements, and brake parts and carb cleaner.

 

Apparently, and without me knowing, my scraper must have slipped when trying to dislodge the rock-hard deposits on the piston, carried bits of the carbon with it, and mildly scratched the cylinder deck radially away from the bore. :dopeslap: By the way, I can just catch my fingernail on the larger scratch. And just feel the lesser scratches.

 

I've read and read on what to do. Aside from having everything resurfaced at a machine shop, I could either attempt to scotchbright and blend the scratches away, possibly leaving a minute depression in the deck surface, OR, carefully razor off any burrs or edges along the scratch, and fill the scratches with high temp RTV or similar before installing the new 4-layer MLS gasket.

 

I'm leaning towards the latter. May I ask for your advice?

 

Here are the pics:

20151228_132848.jpg

 

Zoomed in:

20151228_132848c.jpg

 

 

 

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If it were mine I would simply clean the surface per the gasket instructions and bolt everything up.

 

Do not try to blend or sand out the imperfections. Do not use gasket glues, grease and especially rtv of any type or kind.

 

Do properly torque.

 

I would be more concerned about what may have washed down into the piston rings than those surface scratches.

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I would be more concerned about what may have washed down into the piston rings than those surface scratches.

 

+1

 

How did you keep the cylinder walls and rings from contamination?

 

MB>

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It is recommended that you remove carbon buildup from the top of pistons when doing this service. And with Alum pistons and heads, do so with 'soft' tools like plastic scrapers, wood, and a tool I found very helpful, bamboo chopsticks. They were very strong, could be carved to different shapes, and did little to no marring of the piston surface. For the deck surface, I used only plastic scrapers, paper towels (a very mild abrasive) my fingernail, and brake parts cleaner.

 

Incidentally, I found brake parts cleaner to be a stronger solvent than carb cleaner, but still reasonably safe for the paint/coating on the engine. I also considered Aircraft Paint remover, but did not resort to that. I read that the new environmentally friendly 'Low VOC' Permatex VOC gasket remover does not work at all. Trust me, you want VOCs! :grin:

 

The left side piston had deposits so hard, they looked/felt like rocks/crystals, so I resorted to a metal pick (on the piston only!) and was as careful as could be to not put deep scratches.

 

You can see the piston is at TDC, plus the top of piston is oriented vertically, so very little debris can makes its way into the chamber. Some liquefied/scratched off carbon buildup does try to rest in the narrow crevice around the piston, but I used a blast of brake parts cleaner to clean out, a sharpened bamboo skewer, and compressed air from a can. What little remains will probably be blasted out the exhaust. I watched several head gasket replacement videos by professionals and none of them seemed too worried about microscopic debris. They 'did the best they could'. Plus, logic would tell you that these deposits occasionally break free themselves inside the chamber and are flushed out the exhaust.

 

IF I AM WRONG WITH RESPECT TO OILHEADS, SOMEONE PLEASE SPEAK UP. I can still remove the heads and do further cleaning, possibly moving the piston back and cleaning more, if needed.

 

 

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Working on car alum blocks I would leave old head gasket on while cleaning up pistons with brass brush on small dremmel. Scrape most of gasket off with plastic spatula and then dremmel head surface. I would then remove all the shop rags I had stuffed down ports and cylinders, hi tack head gasket and torque. Pore cheap oil in and start. Run thru rpms for ten minutes, drain and refill with quality oil. Hey,being a GM mech.in the 70s engine oil was cheap and plentiful.

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SnakePliskin it is like going to the dentist and having your teeth polished. You rinse and they use the suction tube then another rinse... all good then 10 minutes later you are chewing on grit.

That grit finds lots of hiding places.

Basically neither the scratches nor any very fine grit residue are likely to cause your engine to fail.

In the eighties the local junk yard would drop off a car for my students to take apart for them. One engine we did a compression test on and it was all over the map. Owner of the yard asked if he could demo how to clean up the carbon quickly. Procedure was warm up the engine, have a large pop bottle filled 75/25 with hot water and ATF that had been shaken. Hold the revs around 2500 and slowly pour the mixture in while keeping the engine running. Repeat. Compression test after cool down was with in spec across all cylinders.

On the other hand I have seen diesels with a very small piece of material caught between piston and cylinder wall that required a rebore/ rebuild.

Button it up and see what you get.... chances are very good it will all be OK.

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Had forgotten about atf trick. It works well for carb vehicles but make sure you do it outside...lots of smoke. Had one nube poor water down carb, that's a no no in large quantities, caused a chunk of carbon to break off...by by engine.

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So there are several comments about debris washing down into the cylinder wall... So what would be the proper procedure for cleaning the pistons and completely avoiding this? Removing the cylinder itself beforehand? If those that have expressed concern have done this procedure, please tell me how you did it.

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Ok, being the type to dwell on the possibility of there being a problem, I've pulled off the left side head again and am prepared to do whatever is necessary to properly clean out the carbon debris.

 

I'm avoiding the water/ATF treatment for now since I've gone this far. I just want to make sure there is no problem with the fine debris.

 

Could I get some advice from someone on this. If you were to manually clean off hard carbon deposits like I'm attempting to so, would you remove the cylinder case and/or the piston to accomplish this? Or would you never attempt this in the first place?

 

 

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SnakePliskin .... you haven't done anything that hasn't been done many times before with no ill effect.

 

I have taken far greater risks doing thread insert replacements for spark plugs with the head on the engine.

 

But for reference if you are doing the job again sometime then doing an engine running carbon clean is the way to go. Standard procedure on some engines for spark plug replacement. There are chemicals available, don't use the water/atf trick on a cat equipped vehicle.

 

Personally I avoid petro chemicals if possible and brake cleaner in particular. Part of that is health issues from exposure and the other from my observation that it can cause more problems that it solves.

 

I would make sure that the top ring is lubed with a small amount of oil brushed on then the excess wiped off. If you can use your can of air to blow the oil into the ring land.

 

 

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So there are several comments about debris washing down into the cylinder wall... So what would be the proper procedure for cleaning the pistons and completely avoiding this? Removing the cylinder itself beforehand? If those that have expressed concern have done this procedure, please tell me how you did it.

 

Before starting, put a ring of grease around the piston, with the engine at TDC. When you finish cleaning, just rotate the piston away from TDC and clean out the grease, which will have trapped any bits than could damage the motor.

 

 

Andy

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Morning SnakePliskin

 

Lots of possibilities on this one.

 

Best way is to remove the cylinder & piston then clean the piston on the bench. Then wash the piston in a good solvent & blow it off with compressed air. (this also allows ring removal & ring groove cleaning)

 

If you leave the cylinder(s) on the engine with piston(s) still connected it gets more involved as you have the cylinder base gasket integrity to preserve & those pesky cam chains to deal with.

 

I usually remove the cylinders myself as that allows new base gaskets to be installed (a point of oil leaks on older oil heads)

 

On the few I have done with cylinder or cylinders left on the engine I usually ONLY do one side at a time as that allows carful rotation of the crankshaft (by controlling only one side loose cam chain)

 

I decarbonize the piston top using nothing that is abrasive, has an abrasive binder, or has anything containing grit (no scotch pad type disks or rotary pads). I do like to use the plastic rotary toothed de-carboning disks in my right angle die grinder as they don't leave abrasive residue other than the carbon particles)

 

If my intention is to try to maintain & re-use the current cylinder base gaskets the FIRST thing I do is slide pieces of pipe or stack of nuts & washers on the cylinder studs then re-install the cyl head nuts & tighten slightly (to hold the cylinder tight to the base gasket (I really don't want to compromise the sealing at the base gasket to block & to the cyl base).

 

Using the pipes/nuts on the cyl studs also allows turning the crankshaft a little so the piston can be run up & down the bore to clean the bore & clean above the top ring area.

 

Once I have the piston top cleaned of carbon (which usually takes a lot longer than replacing the base gasket & cleaning the piston off-engine) I CONTROL the cam chain & move the piston down the bore a ways, then use heavy motor oil to oil the cylinder above the lowered piston, then (carefully) roll the piston back to TDC then clean the oil residue/carbon particles that the piston brought up. Then lower the piston a short ways again & thoroughly clean the bore again (the oil above the top ring on the cylinder wall usually brings up most of the carbon crap in the piston top area above the top ring)

 

As you can see doing one side at a time is almost a must so you only have one cam chain to deal with.

 

As to using water, or ATF, or water oil mix, or anything to clean the carbon-- good luck with that one. Those mixtures will soften & even remove light fluffy carbon but it won't touch that HARD baked on piston top carbon. Even carb clean or brake clean will not soften that baked on carbon until you scrape your butt off on it with a utensil of some sort.

 

 

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Wow guys, I really appreciate the helpful tips from everyone and words of encouragement. I'm going to incorporate these suggestions into my methods.

 

And thank you D.R. for the step by step approach. I like the idea of the pipe method. Going to look for some now …

 

I just have a couple of questions:

1. Several folks have mentioned the danger of moving the piston up and down with the cam sprocket off, and how doing this may damage the cam chain guides if not careful. I'm curious, exactly how do the chain guides get damaged?

 

2. *If* I decide to remove the head and replace the base gasket as a preventative measure, I'm assuming I can leave the rings in place and just carefully clean the piston. Or if I like, removed the rings and replace them at the prescribed angles with respect to each other. If I go this route, is there an alternative method for compressing the rings when inserting, other than ordering the $80 ring compression tool from BMW? This link suggests using the tool over fingernails, but I suspect there are other methods.

 

 

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Afternoon SnakePliskin

 

 

I just have a couple of questions:

 

1. Several folks have mentioned the danger of moving the piston up and down with the cam sprocket off, and how doing this may damage the cam chain guides if not careful. I'm curious, exactly how do the chain guides get damaged?---The chain can jam up or double up & break a chain guide. I DO ONLY ONE SIDE AT A TIME as that allows the other side chain to track on the cam sprocket. On the removed side I hold the chain extended in one hand as a I slowly & carefully turn the crankshaft with the other hand. (you need to be very careful here)

 

2. *If* I decide to remove the head and replace the base gasket as a preventative measure, I'm assuming I can leave the rings in place and just carefully clean the piston. Or if I like, removed the rings and replace them at the prescribed angles with respect to each other. If I go this route, is there an alternative method for compressing the rings when inserting, other than ordering the $80 ring compression tool from BMW?--- if you are real anal you can put the rings back on in the very same clocking (I just stagger the ring gaps & call it good)--the rings are not pinned so do rotate in use so you probably won't be putting them in a place they haven't been before.

 

Just be sure to put the rings back in the same groove & facing the same way.

 

As for a ring compressor you can rent one, make one, buy one or just use a piece of thin tin & a couple of large hose clamps. I have a double screw one that will open up & come apart if I unscrew it far enough & it works. If I was doing a lot of boxer pistons I would buy something better but mine works & the few times a year that I use it I can live with the extra hassle.

 

 

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Thanks!

 

That guidance on the cam chains gives me an idea and that is to insert a secondary channel or guard inside the existing guides that extends out from the heads that prevents the chain from doing any damage when rotating. I am doing one side at a time as you suggest.

 

I read that the rings do rotate around because they are not pinned. That's probably a good thing because it keeps wear patterns from developing. I may use your idea of fashioning a zinc/hose clamp tool.

 

 

 

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In the UK these items are very cheap and readily available at Motor Factors and car DIY outlets. It would work out as cheap as paying postage for a colleague to send one.

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Morning SnakePliskin

 

Most tool rental places have ring compressors as well as a lot of auto parts stores have rental ring compressors. (you just have to call or shop around)

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Correct me if I'm wrong, but I believe you guys are referring to the universal ring compressors that wrap around and tighten. I saw one at Advance Auto for around $25.

 

I was referring to the BMW "piston ring cramp strap" (Part Nos. 11 2 900/11 2 905)

 

At least one poster suggested this tool was designed so as not to damage the base of the piston. Possibly even easier to manage than more manual methods, IDK.

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Correct me if I'm wrong, but I believe you guys are referring to the universal ring compressors that wrap around and tighten.

 

Evening SnakePliskin

 

Sort of-- on the BMW boxer you can't use just any ring compressor as you need one that be taken apart or opened up so you can get it off over the connecting rod. (most of those auto store ring compressors won't come off over the connecting rod)

 

The other thing the ring compressor must do is not be so thin when installed on the piston that it slips between piston & cylinder base when the cylinder is slid over the piston.

 

If you can find the proper BMW ring compressor strap to borrow or buy then that is best but for a single usage you really don't need one.

 

But if you feel better using the BMW tool then by all means spend the money or try to borrow one.

 

I don't do many BMW boxer piston/cylinder installs per year but on the ones I have done I haven't used the BMW strap & haven't ever damaged a piston or ring (but I do work carefully & slowly to assure that each ring is in the cylinder before pushing the cylinder on to the next ring in line)

 

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Thanks for the tips! I was just reading the Haynes manual this morning and it mentioned using the 'fingernail' method if a compressor is not available, so I guess there are several ways to do it, as long as you're careful like you say.

 

 

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Thanks for the tips! I was just reading the Haynes manual this morning and it mentioned using the 'fingernail' method if a compressor is not available, so I guess there are several ways to do it, as long as you're careful like you say.

 

 

Afternoon SnakePliskin

 

I have used the fingernail, popsicle stick, plastic scraper method in the past (mostly on single cylinder engines) but never on the BMW boxer.

 

I would imagine that it would take 2 people to get it done with the least possibility of ring breakage or problems (one to carefully slide the cylinder on as the other person compresses each ring as the cylinder gets to it)

 

 

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Hello again. Having successfully completed the transmission swap, this cylinder and piston cleaning is starting to feel more involved. :dopeslap:

 

I'm now attempting to remove the cylinder drum. It is glued on but good. At 41k miles, I believe this may be the first time the cylinder has come off. (original head gaskets were on there)

 

Anyway, may I request any helpful hints on how to remove the stuck cylinder drums? Haynes suggested rubber mallet but NO prying. I tried that, along with a good hand wrenching, but it has not budged. All four cylinder drum bolts are out (two inner and two outer), and the lower chain guide bolt and chain tensioner pin pieces have been removed (left side). (see below)

 

IMG_8857c.JPG

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Evening SnakePliskin

 

It looks like you already have the piston top clean so why not leave that stuck cylinder on the engine & just back the piston down the bore a bit then oil & clean the upper cylinder wall. (careful with the cam chain as you move the crankshaft)

 

If you just have to remove it then I usually use a rubber or rawhide mallet. Some can be on there pretty tight so persistence is usually best. (just be very careful of the cyl fins)

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Evening!

 

Good advice, I may do just that! I'm guess I'm in full OCD mode now. Just wanted to clean the ring lands and back of piston, plus any carbon I missed on the piston crown, but it looks like I got most of it.

 

Here is before and after. Aircraft Paint remover worked great to soften carbon.

 

Before:

20160101_231312.jpg

 

After:

20160102_123325.jpg

 

20160110_190118f.jpg

 

20160110_190118.jpg

 

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By the way, you can see some minor markings as shown (ONLY on the top and bottom of the cylinder wall). These are more pronounced towards the bottom of the cylinder, and are not deep enough to catch a fingernail. From reading and reasoning, this is probably from the built up carbon on the piston crown contacting the cylinder wall at the bottom of the stroke when there is some lateral force from the angled connecting rod. Hopefully the carbon cleaning will keep this from getting any worse.

 

20160105_204647.jpg

 

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I have no experience with the BMW Boxers but this were a car engine, I would do what dirtrider suggested about light oil on the cylinder walls and button it up. Once buttoned up, run the pistons through full cycle by hand before start up. Great job on cleaning the crowns.

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Morning SnakePliskin

 

You never like to find scratches in the cylinder

walls (especially the hard plated BMW cylinder).

 

But those don't look too bad & remember-- at the

bottom of the stroke there is very little compression

or combustion pressure so bottom-of-stroke is not

a real significant ring sealing area.

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