Randall Washington, aka "Randakk"
President and Chief Executive Rider
Chapel Hill, NC USA
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Return to main Tech Tips Index GL1000 / GL1100 / GL1200 Head Gasket DetailsHead 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 30+ years old. Rare failures are usually caused by inattention and poor maintenance to the cooling system. A simple case of overheating can ruin your head gaskets. Warped heads are also a possibly outcome of overheating! Lately, I've been immersed in GL1000 head gasket issues. As reported recently, I'm upping the drive ratio on my supercharged GL1000 along with a number of other performance upgrades. RC-003 has performed flawlessly in a rather mild state of tune (7.5 pound of max boost). I have been running stock Honda head gaskets with the setup until now without any problems. I have the heads off now for some winter upgrades that will include different cams that are better suited to supercharging. I will be making other upgrades as well including changing the blower drive ratio for a bit more boost. The extra boost I will be making soon calls for a bit more insurance on the head gasket issue, so I am moving to copper head gaskets to maintain reliability. I know that a number of customers are involved in high performance projects that involve supercharging, turbos and nitrous oxide. Once I'm satisfied with the performance, I plan to sell these proprietary copper head gaskets. Copper head gaskets are virtually indestructible. The main drawback of copper head gaskets is that they require machining of the heads (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. However, for most customers - I strongly recommend OEM Honda head gaskets! There are some aftermarket head gaskets in the marketplace that are probably fine. But be aware that some aftermarket head gaskets are not!
GL1000 Cylinder Head and OEM Honda Head Gasket Have you ever wondered why Honda has specified so many part numbers for their head gaskets over the years:
Some of the explanation is due to superseded part numbers.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):
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! There is a fairly prominent web vendor that offers only one aftermarket head gasket part number which it claims covers all 3 models! Heed my advice and steer clear of such head gaskets! This job is too time consuming to do twice. Use Honda head gaskets to be safe. If you insist on saving a few bucks and are set on using aftermarket head gaskets, at least be sure to pick a vendor that understands that one part number can't cover 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 sheet of "true" plate glass. 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 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. Here's a useful link to a lapping tutorial video 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. 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 orings. The "big" end is oriented "out." 12. Make sure all locating dowels are in place. 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 30+ years old. My practice: I install OEM Honda head gaskets "dry." They are impregnated with heat and pressure activated agents to insure 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 cars 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. 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.\ 19. 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 failures. If the tips above are followed carefully, you will have many years and miles of trouble free service! 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