81' CM400 engine rebuild

[Drey6]

To avoid any more future frustrations with leaking head gaskets (were they leaking oil pressure?), after inspecting for any small scrapes or surface irregularities aside from checking for warpage, try using permatex copper coat type head gasket spray. Mask off the cylinder bore, painted portions of block & head, mask off combustion chamber, hang head gasket from a wire/string/coat hanger overhead, and follow the instructions - 2 light coats per surface with 15 minutes in between. Do this right before assembly.

And I only ever really trust OEM head & base gaskets for the most part, as well as block oil passage o-ring and cam chain tunnel o-rings.

The issue of the leak was due to all the crud in the threads for the head bolts. This was discovered upon disassemble so I likely replaced the head gasket the first time with a "false torque" due to gummed up threads. I'm using the DK gasket set that many people on Honda twins have trusted with no problems.

I've actually already purchased the copper spray already! It's on hand... Ready for reassembly, whenever that may be. I may need some head work done, need to double check what condition it's in.

Going to wait till next week (plus a few days) to lightly wet sand and repaint what sections showed some peel and the areas that need more coating.

 

[Chuck78]

I've seen diy tutorials on how to do a quickie valve lapping job using a drill, piece of rubber/poly tubing that has a tight fit around the valve stem, & lapping compound. I was curious about that for some less concerning engine freshening up jobs. On a bigger 4 cylinder I would be more concerned about uniformity of seat height between 4 sets of intake & exhaust valves, and more likely opt for a professional Serdi machine radiused transition valve job. Every seat can be cut to the same depth as the deepest one, for uniform combustion chamber cc volume & uniform performance. If the seats and valves don't look pitted very much upon disassembly, I'd go for the diy lapping. Check valve guide to stem clearance with a dial indicator & magnetic adjustable base 1st. Extensively clean & reassemble with fresh valve guide seals & go. I doubt you'll be buying $$$aftermarket cams, so just verify spec'd height on valve springs and reinstall.

On your gs550-673cc Suzuki build, I'd urge you to get a Serdi valve job and install slightly stiffer than stock springs from MegaCycle or Web cams. The stockers on my 920cc 750 start to float around 10200-10500rpm, and I'd like to swap the .302/280 degree stock cams for some .356 lift 282 degree cams or thereabouts. Not so great without stiffer springs, and that likely means another $100 OEM GS1100G MLS head gasket since I just got turned on to how much more midrange power you can gain with a higher lift cam, & didn't plan on upgrading cams last year when I build the engine. The stock 1st Gen gs400/550/700 cams were wild beasts as you know, very long valve opening duration, hence the gs750 was nearly as fast as the z1/900. They kept the lift more tame for long term durability. I want to bump it up a bit but keep the same duration to keep that gnarly raspy trademark early GS exhaust note!