Oops - head space a little crowded!

[Guest]

One day I had a rush of blood to my head and I decided to rebuild and tweak the engine of my '79 GS1000S.

I had the cylinders bored out to accommodate a set of Wiseco 1085 pistons and I found a local magician who worked on my head to sort out cam end-float and worn cam journals.

Both mods resulted in some machining of the mating surfaces of the barrels and the head. For the head, this will be the second time it has been machined as I had some work done on it during my first restoration about 5 years ago.

After putting everything back together I attempted to turn over the engine by hand only to find that the valves are now contacting the pistons at a certain point in a revolution. (no - I didn't force it once I heard a metallic clunk and things stopped moving )

I used a standard cylinder base gaskets and a Wiseco supplied head gasket.

What alternatives do I have (if any) to increase clearance between the valves and piston crowns?

Thanks,
Ian

[Agemax]

before you think any further, are you 100% sure you have the valve timing set correctly?
I am not saying you aren't a competent mechanic, just it can be a common mistake made by even the best of us.

Worth a check, before you contemplate further work.......

if it is ok, then i believe you can buy thicker base gaskets, or double up on the stock gasket to get the extra clearance you need.

[storm 64]

You could use a thicker base gasket. I'm sure APE sells various thickness base gaskets.

[Kiwi Canuck]

before you think any further, are you 100% sure you have the valve timing set correctly?
I am not saying you aren't a competent mechanic, just it can be a common mistake made by even the best of us.

Worth a check, before you contemplate further work.......

+1 on that, I've done it too.

[tkent02]

Is this a stock cam?

[GregT]

In my experience the Wisecos have enough depth in the valve cutaway for some extreme cams....So yes, either you have the timing wrong or there's been a huge amount taken off the head...

[stetracer]

Cam timing needs to be changed. Increase your lobe centers until you have enough valve to piston clearance .050'' on the intake and .070'' on the exhaust minimum. 106/108 L/C should work to give you more than enough clearance.

[Mekanix]

What's hitting, intake or exhaust valve?

[SqDancerLynn1]

You need to degree the cams !!!

[trippivot]

when you "mill" the head surface or the top of the cylinders you change the location of where the valves are in the combustion chamber during the motion of travel.

The pinch point is towards the outer edge of the valve pocket on the piston top.

NOW you have more than one choice;

one can modify the piston crown by opening the valve pockets just a smidge - hopefully you do not need to work on the cylinder edges.

one can raise the lobe center to avoid the piston/valve interference

one can get a huge base gasket

2 out of those 3 will make your bike slower - or seem slower.

set deck height no thinner than 0.040" and work out the 8 pockets . Check for minimum clearances during all 720 degrees of all 4 cylinders.

goal is to keep the lobe centers under 108. you'll be happier.

[IanR]

Thanks everyone.

I bought a new cam chain but I did not check the number of links before I put it in. So I'll start by checking that the cam chain is the correct length.

Next I'm going to take extra care ensuring that the cam timing is correct - and I think I'll start with ensuring that the ignition "stuff" is put on correctly so that TDC is actually TDC. Finally I'll put the cams back on double checking everything is lined up correctly.

If I had to measure valve to piston clearance, how would I do that?

I'm away for a few days, but I'll let you know how I go when I get back.

Ian

[IanR]

Is this a stock cam?

Yes they are stock.

[Flatline_Racing]

Did you check your deck height?

[IanR]

Did you check your deck height?

You can tell I'm an amateur as I had to find out what deck height is - I found what looks like a good explanation here.

Now that I know what it is I know that I haven't checked it.

If the issue isn't my incompetence in setting up the valve timing, I'll have to take the head off and I'll check it at that stage.

Thanks,
Ian

[IanR]

What's hitting, intake or exhaust valve?

Not sure - I'll have to have a closer look when I get back.