787 R&D Rec Head

[spx800]

Has anyone used the R&D (43cc) rec. head on a stock 787? It seems like you need to use the oem head cover? Also, the water jackets seem smaller then on the oem? Looking for feedback.

Thanks

 

[Matt Braley]

It's a common upgrade. I have had a X4 with one but there were other mods. I don't think you will notice a large difference unless it is combined with more upgrades. A downside is that you would need to run high test with that higher compression if you don't already.

 

[spx800]

More might come later in the future. I currently run 91 since my rx requires it. I've read it's good for roughly 175 psi, can you verify this? Can you use the stock head cover?

I'm conflicted between an AM head and sending the stock one out to group K.

 

[Matt Braley]

Yes the OEM head cover and O-rings are used. The compression increase sounds about right to me.

 

[Spimothy Leary]

i believe that would call for 93 octane

 

[spx800]

Would you change the pistons and rings if you were changing the head? It makes sense, but if the compressions good right now would you still do it?

 

[Matt Braley]

Heck no I would change the piston and rings when they need it. If you have good compression they should be fine.

 

[spx800]

I'm not so much worried about the rings (would just make sense to change them if you're doing the pistons), but more worried about the skirts of the pistons since I believe they're 16 years old (ski had relatively low hours on it when I bought it four years ago). Compression was 155/155 when I checked last fall after putting the ski in my garage. So, I could put the head on, change the gaskets and call it a day?

 

[spx800]

So, i got the head today, but i have concerns. Take a look at the combustion chamber, would anyone try and file down that gouge and run this head with the damage to the spark plug hole, or return it? The ad specified no damage.

 

[spx800]

I also want to add that brand new spark plugs wont thread in. They thread in a few threads by hand then it tightens right up. I shouldn't have to force them and I don't want to run a tap through it.

 

[Sportster-2001-951C-Stock]

Considering those look like they were bead blasted, there may be some of the media remaining in the thread recesses. Try cleaning them with solvent and blast with air and see if that helps any. Sometimes hot water and blasting with air can do a good job of removing fine abrasive out of threads too.

Once the threads are cleaned out then let's have a look at how the plug comes through, torqued in, to determine if the damage could use relieving (I tend to think it's a good idea to take off the burr that might become a hot spot and cause pre-ignition).

 

[Sportster-2001-951C-Stock]

Compression was 155/155 when I checked last fall after putting the ski in my garage. So, I could put the head on, change the gaskets and call it a day?

155 sounds good to me, especially if the skirts and bores aren't scored I'd go with it. Eventually it'll have to come back apart but plans change so why spend money on that now?

 

[spx800]

Considering those look like they were bead blasted, there may be some of the media remaining in the thread recesses. Try cleaning them with solvent and blast with air and see if that helps any. Sometimes hot water and blasting with air can do a good job of removing fine abrasive out of threads too.

Once the threads are cleaned out then let's have a look at how the plug comes through, torqued in, to determine if the damage could use relieving (I tend to think it's a good idea to take off the burr that might become a hot spot and cause pre-ignition).

That was my thought as well. I'll try the hot water and air for the threads. Three threads where that burr is, are damaged, so i might have to run a tap regardless.

 

[spx800]

I tried hot water and air twice and it didn't seem to make much of a difference. I'm going to try and run a wire brush through them. At this rate the plugs won't thread through by hand.

 

[Sportster-2001-951C-Stock]

Could be they bead-blasted the threads and rounded them over.

 

[spx800]

Could be they bead-blasted the threads and rounded them over.

You're probably right. I'll run a tap through them tomorrow.