XJ750RL mods/build

Frap, I sent you a message.

 

Check your inbox I have the part, you can have it.

 

As discussed Bushy, here are the pics.

 

What? You can't just swap a cap - they are inline bored once dowelled to the head, it might work but at the very least you should test fit it without the cam, then with it using some plastigauge. I've done this on car heads by selecting the best fit and testing this way, but there's no guarantees.
I once skimmed a 1100 vw head for a local lad, asked him how it worked out. He said the caps were getting hot. He had just assumed they fitted anywhere, result - scrap head, really.
Wash it and weld it would be my suggestion.

 

This is true, and this is the correct procedure to follow.

 

I checked the valve clearances not long ago and 5 of the 8 are out of spec.

The new shims required in accordance with the Haynes book are only 1 shim size away from the current ones. I don't know if these shims currently in the bike are the out of factory shims, but would one shim size in difference be enough to make an audible tap/knock sound whilst idling?

 

post your numbers for shim and clearances some charts in haynes books are wrong

 

The valve clearances tighten up as the engine accumulates hours; so when the tap goes away, that's when you start to worry.

There is also a tapping noise that is associated with one of the cam caps allowing a bit more end play than Yamaha intended (though your RL should have been fitted with the revised cam cap). If the tap is coming from the right side of the cam cover, that's the issue. It can be ignored as the clearance isn't large enough to do anything other than make a bit of noise (per the Yamaha TSB).

The third source is from the alternator chain contacting the case and an oil jet when the alternator chain guide fails. That tap will be louder, a bit hollow sounding, and increase as you pull away, or allow the throttle to slam shut (unlike the cam tap, which quiets down as engine revs increase, and does not get louder than from rapdly shuting the throttle from an off-idle conditon).

If you can post a video we can help you identify the source of the noise. My inclination is to say that it's just the usual valve noise.

 

looks like you can swap 2 shims and buy 3 shims
E3 move to E1
I1 move to I2
your chart in your book is correct

 

sounds like an exhaust leak?

 

Just went to check that and appears one of the screwshas threaded the head... the tapping does sound like it is internal however until I retap this exhaust thread, won't be certain.

 

So, I've now taken the exhaust off. I knew there was some damage to the exhaust 1 of the head but now that I've got a clear view, there's a crack in the thread area of where one of the exhaust screws go. The thread that was in there was half out so I've taken it out.

Queations:
1. How f***ed am I?
2. Is the thread that I've removed, replaceable or is it a matter of re tapping?
3. The crack in the head, opinions on how to fix. Should I rethread, put a bolt in and then weld it?

 

that's a Helicoil you took out, i suggest you put another back in. and keep your fingers crossed

 

That's a helicoil that you pulled out. Ideally the crack should be welded, but it's not too deep so you might be OK cleaning it good and filling it with epoxy.
You can fit a new insert, or if you elect to have the crack welded the shop can fill the hole and tap it like brand new.

 

Ans you noticed, you have an exhaust leak.
The valves sound wonderful, and there's no sign of alernator chain slap that I can hear.

 

I did a little looking and as mentioned above, learnt its a helicoil. I guess my concern of putting a new helicoil of the same size (M6) would be that it doesn't sit tight due to the now slightly wider spot because of the crack, thus pulling out again.

Given that it looks like the hole depth goes deeper than where the original helicoil sat, I'll go a new M6 helicoil in the deep section and use a longer bolt. Along with some epoxy to strengthen the crack.

Once again, thanks guys.

 

the crack was there first i think. then the PO tried the coil to fix it. you'll need a drill bit the right size and the special tap to install it. look up internal thread repair, some people say helicoil isn't the best
it's the only kind i've used

 

Oh, so the helicoil isn't a stock thing? Thanks for that.

 

Helicoil is the only brand of threaded insert used in aircraft (that I am aware of anyway). They've literally been holding airplanes together since the 1930's, and in that application are put into brand new parts prior to assembly (aluminum threads wear poorly, with engine teardowns being an annual event).