Cylinder head.

Hi Guys, Can anyone tell me if the seca and maxim cylinder heads are the same. I had a bent valve (inlet) and rather than replace the valve I changed the head with a maxim head I had in my shop (shed), however it wont run, all the settings have been gone over again and again but still no luck. My other option would be to pull the maxim head and take the required valve out and put it in my seca head, again always assuming the valves are the same. The seca is an 81, the maxim year is unknown. Thanks Davy.

 

So from your avatar, I'm assuming you mean specifically the xj750 maxim vs. the xj750 Seca?

Or do you mean the:

xj400 maxim vs. xs400 maxim vs. xs400 Seca

xj550 maxim vs. xj550 Seca

xj650 maxim vs. xj650 non-turbo seca vs. xj650 turbo Seca.

Just to clarify for someone else who may not see the pic...

 

Yes I never gave it a thought. It is a XJ750 seca,

 

you can look up the part number on
www.yamahapartsnation.com

partial list for you for 81 seca xj750
http://www.yamahapartsnation.com/oemparts/p/yamaha/5g2-11101-00-00/cylinder-head-assembly on what will fit

 

Or you can just ask Len

 

All XJ750 heads (Maxim, Midnight Maxim, Seca 1981-83) are all the same (besides color) and will completely interchange with each other.

 

Thanks, I guess I have to figure out why it wont fire up.

 

The first thin'g I'd check is to make sure you don't have the cam timing out by 180º.

 

If it was 180 degrees out, wouldn't the pistons hit the valves?

 

I will check that out. Thanks.

 

God I hope not, I have all the tools, I just did not want to pull the head again. Thanks

 

If the cam were 180 degrees off, I would have thought that would flip the firing order, but would otherwise run, as XJs use wasted spark. No?

I mean, when 1 is at TDC for compression, 4 is at TDC for exhaust. The cam turns once for two crank rotations. If the cam was one crank rotation off, the only difference would be that 1 would be TDC for exhaust and 4 would be TDC for compression, instead. Net effect would be no change since both cylinders get spark near the top of the piston stroke every rotation of the crank.

Now, if the cam were 90 degrees off, one direction or the other, that would be a different story.

 

Think you would have noticed that...it would probably not crank

Yes, that's what i mean, 180 degrees on the crankshaft would be 90 on the cams....that wouldn't be nice....
Otherwise it should run....?!

 

Yes. Pretty sure these are interference engines. That arrangement would mean pistons at TDC when cam expects them at BDC.

 

Well guys, thanks for all your help, it will be a little time until I get to it, as I have a smashed up left foot (dont ask), at least the bike SV650S came out of "it"
in good shape,guess I should stick to the Seca. Any more thoughts or impute greatly welcome.

 

Let's hope you and your seca gets better soon....
I like your setup with that round headlight and speedometer, i'm planning on something like that for mine too, do you know what meter it is and does it work well?

 

I got the bike with this set up fitted. The wires had been subjected to ignorant butchering to remove the electronics so that took some time to sort out. I think it is xj650 gauges and they do work well, it is an electronic rev counter and the original connection plugged rite in and works beautifully (thank goodness) , The starter motor chain guide was falling apart and the local bike shop gave me a loan of his four way alternator puller which meant rotating the engine backwards which eventually led to my bent valve. So don’t cheap out folks spend the $20 and buy the extractor . the headlight is to big at the back to allow for the cables and harness,quickly sorted with an angle grinder. So when I get the ''head thing'' sorted by redoing my timing or replacing the bent valve in the original head we
will see, I just hate shelling out for another head gasket . I will post the final outcome,It will run again.Promise.

 

Didn't really get it all there....language you know....:-S
But thanks for the information about the meters, i already got the headlight, think it's a little smaller though, hope it will fit well.

 

C'mon... You throw that out there and really expect us NOT to ask?!?!?

So, what happened?!?!? Obviously either:
1. A really good story
2. A real bonehead story

Dave

 

OK. I was in an intersection turning left and was hit by an impaired driver coming toward me also turning left, claims he never saw me(how original )and he side swiped me
turning my left foot to mush. this was in the spring and I am still in a cast with a foot full of plates and pins, you decide, #1, or #2. Take care guys, you never know when.

 

Driver was impaired by his own bonehead

 

The twat stood beside his car crying and sobbing , looking for sympathy I suppose,(he got none) he was lucky I could not stand or he would have known what pain and misery
really feels like. As I said take care guys, my xj project is on hold because of this retard.

 

SYMPATHY?!?! Hard to sympathize with a fool, unless you feel sorry THAT HE'S STUPID! or sorry that he's alive. He was the instrument of his own demise.

 

What stood by his car? ( that didnt go un-noticed..... I can't believe Matti didn't say anything---lol) ROTFLMAO

 

The "twat" slang for female genitalia(him)

 

Haven't heard that word before....now i know, thanks to google....
In sweden we call it a fitta.

 

Sorry dave. I was too pissed aboot the drunk driver to think of twat. New baby is making me soft.
Too soft for twat... who's gonna touch THAT one? winkface!

 

Hell I am 59 and twat is never far from my mind,out of reach perhaps, but not out of mind.

 

OK Guys, I replaced the two bent valves in the original head and all is well in my world, my foot is good to go, a bit painful, but if I wear my riding boots gear changes are fine.

 

Just in time for tornado...I mean riding season.