Valve Tappet too Small 1.6-1.8mm?

[Roland]

1978 GS750E @58K miles
Any ideas what would cause my intake Valve #1 to indicate the need for a shim size between 1.6-1.8mm?

I removed a 2.55x shim and used my feeler gauges and determined that I need to replace the 2.55x with something much smaller in the range of 1.6-1.8mm. Although all the shims need to be replaced, they at least fall within expected range. According to the manual optional shims are in the range of 2.15mm~3.10mm

[BassCliff]

Hi,

Put a 2.50 in there and re-measure.


Thank you for your indulgence,

BassCliff

[Roland]

Valve # 1 beyond spec.

I can't put in a 2.5 and measure. When I took my 1.6-1.8 measurement, that was without any shim installed.

P.S. I am working on it now with the Laptop monitoring the forum.

[BassCliff]

Hi,

Please forgive me for being dense. I'm just not following you. Why would you measure without a shim installed in the bucket? Are you using a tappet tool to push the bucket down to insert and remove the shims? Are you turning the crankshaft so that the lobes are pointing in the proper direction when you measure? (Don't turn the crank if any shims are missing!) Are there two shims in that bucket?

If your valves are that far out of spec then your motor needs major surgery.


Thank you for your indulgence,

BassCliff

[Roland]

Valve # 1 beyond spec.

Thanks for your help BassCliff

Only 1 shim in each bucket. Smallest shim I currently have is a 2.5. If my smallest feeler gauge .04mm will not go in with the 2.5 then I use the tappet tool remove the shim, insert feeler release tool, move the feeler gauge to test for tightness, insert the tappet tool change my stack of feelers and retest. The cam is turned per the manual instructions for intake # 1 at 12 o'clock.

[BassCliff]

Hi Mr. Roland,

I'm sure that the valves had never been checked on my bike when I bought it. The first time I checked the clearances I had to go down two shim sizes on two or three of the valves. It's not uncommon if they have been neglected.

If you've removed a 2.55 and replaced it with a 2.50, and you still don't have proper clearance, try a 2.45 shim.


Thank you for your indulgence,

BassCliff

[zathros]

If the valve seats in deeper into the valve seat, you will need a smaller shim. If the shim wears, you need a bigger shim, if the cam wears, that just plain sucks, but you will need a bigger shim.

[Roland]

Valve # 1 beyond spec.

The problem is that by my estimates it appears as though I need to have a shim somewhere in the neighborhood of 1.6mm which is not an option according to the maintenance manual's optional shims.

I am wondering why it would be that far out.

One thought is if somewhere in its 48k life before I got it if maybe someone changed the valve and used too long of a valve stem. If so then if I were to be able to find shims in that range then all is well but I wanted to ask our GSResource experts before I proceeded down that road.

[Nessism]

Others reading this thread may not understand all the problems with that head Roland. You might want to post the photos here so everyone can understand.

Bottom line is that I think the head is damaged; the head has severe wear on the cam bearing journals. My guess is that the cam is sitting down into the worn journals which has moved it closer to the valve thus messing up your clearance measurements.

I suggest you start looking on ebay for a good used head.

Edit: link to the thread showing damage to the head... http://www.thegsresources.com/_forum...d.php?t=142558

I'm sorry Roland, I didn't spend much time reading your posts about the problem in your other thread and just sent you off that cap without thinking. If I had I would have done a hard stop and fed you the hard reality about your trashed cylinder head.

[zathros]

Extremely worn valve seats can do that too. Either way, it sounds like the head is tired.

[Dan Ruddock]

If all four cylinders were running before you took it apart you are missing something because if it was that far out that cylinder would have no compression. Dan

[Nessism]

Photos from the other thread

[zathros]

Judging from that picture, that head is dead, kaput. Don't put any money or time into it, you need a good used one. I'd check the pistons and rings because usually after you fix the head you find out the rings are weak and realize you need to rebuild to whole motor.

[Dan Ruddock]

That head is not worth fixing as there are many good heads out there for cheap. Dan

[Roland]

Valve # 1 beyond spec.

I was riding the bike every single day back and forth to work and even rode it about 50 miles and had it up to 90+mph the morning before I started the work. Last fall I drove it 1600 miles round trip from Rochester to Kentucky.

The GS750E model is/was so bullet proof that what ever originally caused the problem caused the Cap to get worn as you see the in pictures. This wear allowed the Intake Cam to move vertically between valves 1&2. In essence by it grinding itself down, it has been able to work for who knows how many years in that condition. God I love this Bike & Engine - You just can't break them. I was only doing the shims because to my knowledge they had never been done and I wondered how much it would improve the performance.

The lower section of the bearing shows signs of wear as well but not quite to the extent as the top bearing. To give it the TLC it deserves, I purchased some 500 & 1000 grit sand paper to clean up the lower section guessing that just shy of replacing the head, I would see if I can find the smaller shim and see how she runs.