Honda GL1000 / GL1100 / GL1200 Head Gasket Details

Head gaskets on early ‘Wings are ultra reliable. The vast majority of these bikes are still running flawlessly on the original, factory-installed head gaskets which are now 40+ years old. Rare failures are usually caused by inattention and poor maintenance to the cooling system. But, a simple case of overheating can ruin your head gaskets. Warped heads are also a possibly outcome of overheating!

Head Gaskets

GL1000 Cylinder Head and OEM Honda Head Gasket

I know that a number of customers are involved in high performance projects that involve supercharging, turbos and nitrous oxide. Copper head gaskets are virtually indestructible and recommended for such high performance duty. I have used them on my own supercharged GL1000. The main drawback of copper head gaskets is that they require machining of the heads and/or block to install special stainless steel wire “orings.” These are necessary to generate the engineered clamping forces since copper does not compress appreciably and will move laterally unless it is “captured” relative to the bore. Another issue is that copper has no sealing ability, so gasket sealant must be used. Also be prepared for some nuisance coolant leaks with coper head gaskets that usually disappear.

For most customers – OEM Honda head gaskets are an excellent choice. Randakk’s offers an excellent aftermarket head gasket kit as well.

Other aftermarket head gaskets in the marketplace that are probably fine. But be aware that some aftermarket head gaskets are not! 

Have you ever wondered why Honda has specified so many part numbers for their head gaskets over the years:

12251-371-003 (GL1000)

12251-371-010 (GL1000)

12251-371-306 (GL1000) – current part number

12251-463-000 (GL1100)

12251-463-003 (GL1100)

12251-MG9-000 (GL1100 / GL1200)

12251-MG9-306 (GL1100 / GL1200) – current part number

Some of the explanation is due to superseded part numbers. That happens as Honda changes vendors and continuous product improvements are made. But the main reason is connected to the fact that 4 cylinder ‘Wings all have different bore dimensions (all had the same stroke at 61.4mm):

GL1000 = 72.0 mm

GL1100 = 75.0 mm

GL1200 = 76.0mm

Head gasket designers know that there is an ideal geometry and relationship of the armored crush ring aspect of the gasket and it’s proximity to the engine’s bore. Any departures from this “ideal” represent a compromise that has a negative effect on function and reliability. Honda felt the 1mm bore difference between the GL1100 and GL1200 models was close enough so that both engines could be accommodated by one part number.

However, the GL1000 was not included in this thinking and still retains its own unique Honda head gasket part number. Honda clearly feels that the 4mm bore difference between the GL1000 and GL1200 models is too great to “bridge.” I wholeheartedly agree.

Also, even though engines have perfectly round bores, the “dome” in the heads and the corresponding openings in the head gaskets are not perfectly concentric. Well-engineered head gaskets have subtle deviations from “round” to allow proper clearance for the valves.

Beware!

For years, a fairly prominent web vendor offered only one aftermarket head gasket part number which it claimed covered all 3 models!  This job is too time consuming to do twice, so steer clear of any aftermarket head gaskets that claim to fit all 3 models!

Consult the Factory Manual – Section 5 for full details on head gasket replacement. The job is straightforward, but rather time-consuming. Attention to detail is the key to this task! You must have access to the manual!

Here are some additional Head Gasket Replacement Tips:

1. The engine block and head must be surgically clean!

2. 100% of the old gasket residue must be removed without gouging the soft aluminum. Many methods will work. Be safe and use a slow, tedious method. Pro mechanics may use power tools for this step; however, that’s not recommended for amateur mechanics. Take precautions to keep debris out of the engine block openings.

3. Check the head and block for trueness using a precision straight-edge or sheet of true plate glass. It is a good practice to “surface” the head slightly with 220 grit sandpaper affixed to a large sheet of true plate glass. My method is to “color” the entire surface of the head with a Sharpie marker, then sand gently in a “figure 8” pattern until all evidence of the Sharpie marking is gone. This will reveal “high” and “low” areas or any other irregularities. The goal is not to remove lots of material…just verify trueness. Obviously, the use of sandpaper requires that the head be cleaned with warm water and detergent, then rinsed and dried thoroughly.

4. Check all critical components to make sure they are within spec: valve stems, valve guides, rocker shaft, rocker arms, valve springs, cam lobes, cam bearing journals, cam bearing ID in the head.

5. The valve seats (in the heads) can be “ground” but that is rarely necessary.

6. The valves themselves have a special coating and can not be ground. Grinding will ruin them!

7. But, the valves can by gently “lapped” to the heads using fine lapping paste.

8. Always install new valve stem seals as part of a head job…no matter how good the old ones look.

9. Be sure the valve cotters (“keepers”) are fully seated.

10. The final step before bolting up the heads: clean both the head and block with rubbing alcohol to remove any oily residues.

11. Make sure the oil orifice passages are in place and have new o-rings. The “small” end of the oil orifice passage piece is oriented “in” toward the engine block. Important: each oil orifice passage piece gets 2 o-rings. The small o-ring measures: 4.1 x 1.5mm. The placement of the small o-ring is obvious. It goes in a “groove” on the oil orifice passage piece (small end). When installed, the small o-ring disappears just inside the engine block. The larger o-ring used here measures: 6.5 x 1.5mm. Its placement is not quite so obvious. It mounts onto the larger end of the oil orifice passage piece…filling the gap between the passage piece and the head gasket. There is no “groove” for this larger o-ring. Do not forget either of these vital o-rings! My practice: install the oil orifice passage piece with the small o-ring in place into the engine block. Then, install the larger o-ring over the oil orifice passage piece. I find this easier and less likely to create mistakes when mating the head to the block.

Oil O-ringLarger o-ring for oil orifice passage piece goes here

12. Each head has 2 locating dowels. I recommend that these be replaced with new dowels. Old pitted dowels can prevent the head from seating fully “home” and cause the whole job to fail! The corresponding holes in the head and block should be cleaned thoroughly. I use a small brass brush on a Dremel.

13. Section 5, page 19 of the official GL1000 workshop manual recommends the use of “liquid sealer” but does not get any more specific. Plus, that information is 40+ years old. My practice: I install OEM Honda head gaskets “dry.” They are impregnated with heat and pressure activated agents to ensure a proper seal for the oil and coolant passages. Adding any “gasket sealer” to the equation might compromise Honda’s engineering and invite disaster. Decide for yourself, but if you ever want to test this and waste $40.00, torque down a new Honda head gasket. Then come back the next day (without firing the engine) and remove the head. You will be amazed at how well bonded the head gasket is without the benefit of a heat cycle! Note: this “experiment” will destroy the new head gasket!

14. Both gaskets are identical, but they are not symmetrical! Be sure the lower oddly-shaped aspect of the gasket matches the corresponding shape on the block.

15. Unlike modern car engines, the head bolts on these engines can be reused. They should be carefully inspected and the threads cleaned. Be sure the threads in the block are absolutely clean as well. If the threads aren’t clean and perfect, torque values will be corrupted!

16. Use a very light application of molybdenum disulfide grease (“Moly” paste) on the head bolt threads and under the heads of the bolts to ensure accurate torquing to full engineered clamping pressure.

17. Torque carefully in the sequence and stages outlined in the Factory Manual. Use an accurate torque wrench and proper technique. Torque the six 10mm head bolts first, then torque the small 6mm bolt last. I make 3 passes in the recommended sequence to arrive at the final recommended torque value (50%, 75%, and 100% passes).

18. Be aware that in 1978, Honda changed the torque spec for all GL1000 cylinder heads to: 5.8 – 6.2 KG-M (42-45 ft-lb).

19. I recommend that all new head gaskets be put through a heat cycle and then re-torqued. I use 100% distilled water for this step. The heat cycle should be done with no pressure in the cooling system (radiator cap off). Let the engine cool completely and then re-torque. For this final re-torquing, I recommend that each head bolt be cracked slightly loose and then re-tightened to specification following the recommended torque sequence pattern.

20. Always use the correct coolant. It should be a “non-silicate” type. There are many suitable brands available. I use the Honda brand of premixed coolant. There is some evidence that links the use of old-fashioned antifreeze containing silicates with “scouring” of the head gaskets and premature failure.

201. Final Tip: The normal procedure is to remove the carbs and coolant tubes to do a head gasket job. I’ve found that that is not really necessary – especially if you are certain the coolant o-rings don’t need replacement. They are a hassle to replace correctly and they can be left alone if they are not leaking. If you are doing only one head gasket, you can leave the carbs in place. Support the side you are working on by gently wedging suitable blocks of wood between the engine and carb assembly. BEFORE you remove the head bolts, remove the intake manifold bolts and the two screws at the coolant tube flange. Then you can CAREFULLY separate the intakes and coolant tube flange with a slim, sharp-edged wedge tool. Important: you only want to separate the seals…not move the parts any appreciable distance! Then, proceed according to the normal procedure. You will still want to renew the intake o-rings and the coolant flange gasket. Refitting the refurbed cylinder head is slightly trickier but not bad considering how much work you just saved! This also applies if you’re doing both head gaskets. In that case, leave the carbs in place and support with bungee cords.

Head GasketPhoto shows head gasket repair without removing carbs or coolant tubes 

 If the tips above are followed carefully, you will have many years and miles of trouble-free service!

 

If you want to find the best selection online for motorcycle parts, visit our stores below:

www.DimeCityCycles.com | www.Z1Enterprises.com | www.Randakks.com | www.MikesXS.net

 

Comments

  1. Randy Curtis says:

    On a previous post I forgot to mention that if using the aluminum paint on solid copper head gaskets that if you have to pull a head because of some type of mechanical failure the best success I’ve had on reusing the copper gasket is to grab an old bath towel that you don’t care about and lay it out and pour acetone one end and then lay your gaskets on the wet end. Fold the dry part of the towel over the gaskets and then pour more acetone over that. Use a copious amount of acetone and let it sit for approximately 3-5 minutes and then wipe all the paint off using the already ruined towel. Any remaining residue should come off easily with another acetone damp shop towel or rag. Then you are ready to repaint and reuse.

  2. Randy Curtis says:

    I have owned a machine shop since 1978, (getting to be an old guy) I have found after many years of running copper head gaskets on blown alcohol engines that an old trick that many people used in the late 1950’s on steel shim gaskets works great. I have tried products that set under heat and pressure, have used silicon sealers around water jackets and all sorts of things others have suggested. The one that has never failed me is to use a high heat Rustoleum aluminum paint. It has a very high aluminum metal flake content and will fill in any small imperfections between the headgasket and block or gasket and head. The procedure I’ve use has been to clean the gasket and all surfaces with acetone to remove any oil or residue, then paint a light coat of the aluminum paint, followed by another light coat a few minutes later. Last and at this point all your studs, bolts and parts being used should be clean and ready for assembly a third heavy coat of paint and while still tacky install and immediately assemble. You should get a small amount of the paint squeeze out at the perimeter of the head. It’s very important to do each head separately following this procedure as trying to do both at the same time often results in the last coat of paint being to dry to still move around when torqued. By following this procedure I have NEVER had coolant leakage of any kind. There are also head solid copper gasket manufactures that split the gasket around the inside of the cylinder bore and insert an o’ring so the block or head does not need to be o’ringed to stay in place. It is actually sandwiched inside the copper shim. This same company also applies a bead of sealant around the water jackets. This works but it is easy to nick the sealant and only good for the initial install. I’ve had better luck with the aluminum paint and actually reused their gaskets after removing the factory sealant which invariably sticks and tears on disassembly. I’ve done this on automotive assemblies as well as motorcycle’s. Again zero leakage of fluids. All of my stock Honda’s have had headgasket failures after a year or two of my riding, I tend to run the poop out of all my equipment, over rev-sustained high rpm long trips etc. and after a period of time they have all started giving the pleasant aroma and white smoke of anti-freeze leakage. The copper gasket and paint has never failed me. It’s a little time consuming, but it has been a one time fix when done properly. Being an older guy I absolutely hate having to work on my bikes and I’m sure as heck not going to start putting around on them just to keep the stock gaskets alive.

  3. I purchased your Gasket set and Carb rebuild kit in the process of getting the heads cleaned the machine shop noticed the valves were pitted. Its a 1200 and i notice the 1100 exhaust valves are 32 as are the 1200. Can I use them? I see the intakes are bigger on the 1100 are there any out there I can use for intakes on the 1200

  4. Tom Ireland says:

    In the above article you say “valves themselves have a special coating and can not be ground”. Does that include the top of the valve? I have a fair bit of what I believe is carbon on the face of the valve. I would like to use a grinder with a brass wheel brush to remove as much as I can. Is that possible to do, or not recommended?

  5. i put new head gaskets on my 1200 after 70 miles i have oil in the water can i just retighten the head bolts

  6. Tom Vangessel says:

    I have a knock under one of my head’s I have a 82 Honda Goldwing and I cannot figure it out does anyone know what that could be

  7. will GL1000 heads work on a GL1100 and which head gaskets should i use.

    • Norton Muzzone says:

      Ken,
      To answer your question directly no, they are not interchangeable. They have two very different cylinder dimensions.
      Thank you for your inquiry,
      Randakk Customer Service Team

  8. Mariano Vico says:

    HI friends, do you know where can I find those oil orifices (part 12238-371-000) ? Thanks !

  9. Hello,

    I have a 1976 gl1000 and she start up fine but I’ve notice a little drip of oil dripping from the timing belt cover and from the left cylinder. Do I need a new Head Gasket?

    thanks

  10. L. T. Damgaard says:

    You recommend the cylinder bolts re-tightened after a non pressure warm up. Do i have to slightly loose one bolt and re-tighten one after one, or loosen all bolts and re-tighten after Warp up sequence?

  11. steve white says:

    looking at your site for head gasket replacement, great information. the last picture in the tips shows the head gasket a copper color was it sprayed with copper coat? and do you recomend doing that . thanks for the help.

    • No that’s a custom head gasket I had made out of sheet copper for a supercharged bike. Not recommended due to minor nuisance cooling leaks and the difficulty in installing metal “orings”in the head /block. Orings are mandatory when using copper head gaskets. I’ve since reverted to OEM Honda head gaskets on that bike.

Speak Your Mind

*