Head Removal

[karlhoffman_76]

Hi all! I will need to replace valve stem seals in the not too distant future, confirmed by ash fouling on spark plugs and rough idle after several months of ash buildup. Is it possible to remove the head in-situ without removing the motor?

I also read somewhere that if you remove the head you should also replace the gasket between the crankcase and the cylinder block, though this seems unnecessary unless also removing the cylinder block. Is there any truth in this?

When removing the head, are there any notable obstacles that I should be aware of?

Thanks!

[haybaler]

"Is it possible to remove the head in-situ without removing the motor?"

[Armandorf]

you can, removing everything before, like the camshafts.
The gasket should be replaced every time, it seals by compression, and remains "stamped"filling the voids.
also change the bronze washers

[karlhoffman_76]

"Is it possible to remove the head in-situ without removing the motor?"

Apologies for the late reply, and thanks! I found it in the Haynes manual as well, though I couldn't recall any mention of it previously.

you can, removing everything before, like the camshafts.
The gasket should be replaced every time, it seals by compression, and remains "stamped"filling the voids.
also change the bronze washers

Yep, replaced the gasket, didn't replace the copper washers though. I totally forgot to order new ones, but I managed to get the old ones all back on, only a few of them needed a little encouragement!

I only got round to doing this job this weekend past. It was a Buddha Loves You of a job, though I have some experience from rebuilding a CBR250 motor many years ago. Though unlike that motor, 4 valves are a lot easier to remove, replace stem seals and lap than 16! On the other hand, dealing with a timing chain as opposed to geared cams sucked.

The tasks I completed were:

1. Checking the cylinder head mating surface after cleanup for warpage as per the Haynes manual, with a Toledo PRECISION straight edge (< 0.03mm tolerance), which passed.

2. Replacement of all four valve stem seals.

3. Lapping of all 4 valves.

Here are my tips for anyone else out there:

1. Be extremely careful about dropping float shims from the cams, washers and the timing chain through the cavity into the crankcase. I had a few scares with those copper washers when yanking the head off the cylinder block. For anyone wondering, those copper washers are essentially pressed into the threading of the head studs when fully torqued down, so its almost impossible to remove at least a few of them with your hands alone. I was able to "unscrew" some of them, like a nut, and the rest came off with no problem, but the ones that are stuck on the studs are a risk when yanking out the head. probably wouldn't hurt to tape them down with duct tape before doing this. Also use some fencing wire to hold the chain up out of the cavity, it will slide in if you try and drape it over the side of the head.

2. Don't be afraid to use a small BRASS wire brush with a suitable degreaser/lubricant on the head mating surface to remove gasket material. I used to think this would damage it, but it won't. Same for the carbon buildup on the cylinder cavities and valve seats/valves.

3. Pay very close attention to which shim retainers (buckets) belong to which valves as there are slight differences in the manufacturing tolerances, enough to affect your clearances. I got distracted in conversation with someone when removing the exhaust buckets and forgot which one belonged to which valve. This caused me to second guess myself at the end when I was throwing the cams back on and almost led to an existential crisis. For whatever reason, my random 50:50 choice ended up being the correct one anyway (there is a god after all?).

4. Finally, when checking the cam timing once the cams are back on, DO NOT rotate the crankshaft a few degrees in both directions to check for snagging of the cams WITHOUT the cam chain tensioner in place first, like as is suggested in the Haynes manual. This caused the chain to skip every time I followed this advice, which caused me to have to remove the exhaust cam journal caps, reposition the exhaust cam to the correct timing and torque down the journal caps again about four times. In the end I realised that I needed the tensioner to check anything timing related without messing it up. This also almost caused an existential crisis, and is the reason I officially hate cam chains now!

5. Recheck valve clearances once everything is back together, I was surprised to see how my exhaust valve clearances have gone from 0.15 mm back in November to 0.07 mm now, whereas my intake valve clearances have only gone from 0.07 mm in November to 0.05 mm now. I wonder if lapping has anything to do with it, suspect it might.

Observations about how performance differs after doing this job:

1. Startup requires less cranking and is more gradual with the choke on. I assume the reason for this is the absence of motor oil entering the cylinder due to leaking stem seals, the motor oil damping ignition on startup. The additional cranking would have ingested more fuel, and so when ignition did eventuate, it was a lot more sudden and violent.

2. Idle was still a little rough, until I put a wire wheel to the spark plugs and cleaned them up again. Idle is now very stable.

3. Idle speed became lower than before, but a lot more stable. I have readjusted idle since and it sits at 1200 rpm warmed up now.

Anyway, that's my story, I hope it helps someone else out there. If I think of anything else, I'll add it later.

Peace

[cbrfxr67]

Great tips.  How many miles did you get on it before you did this job?

[karlhoffman_76]

Great tips.  How many miles did you get on it before you did this job?

I started to notice the ash fouling around 60k km, but did the fix at 70k km, so maybe 37k to 43k miles?

Now that I think about it too, another thing I've noticed now that I've done the fix is the backfiring has gone away.