XJ550 Seca engine rebuild help

To make a long story short, the cam chain on my XJ550 Seca broke. Somehow the journal holding the cam gear on the front camshaft also cracked. On initial observation, it looks like only one valve was damaged ad I think the pistons are ok, but I haven't fully investigated that yet.

I have been able to find a used top end with camshafts, which is in good shape and the right price. However, this is a Maxim top end. As far as I can tell, the Maxim and Seca used essentially the same engine so this top end should e compatible and work with my Seca.

The one difference I am aware of is that the Maxim and Seca camshafts have different valve lift measurements. The Seca cams have greater lift.

My assumption is that if I put the Maxim top end on it would work, but the decreased valve lift would cause me to lose some performance.

If the maxim too end will work, my next question is if I put Seca camshafts on he Maxim top end, would the valves be capable of handling the increased lift. And if the Maxim valves could handle the increased lift of the Seca cams, would this essentially be equal to a stock Seca engine?

I hope this makes some sort of sense.

Any suggestions or advice will be greatly appreciated.

I am kind of looking forward to putting together this Frankenstein engine!

 

I tried putting up a picture of the broken cam journal, but I am having trouble uploading.

 

It makes complete sense; especially since using the Max cams would require carb changes. (The other difference between the motors.)

The valves are the same, the only difference is the cams themselves so you should be able to run the Seca cams in the Max head IF they check out ok, journal clearance-wise.

Pop 'em in and Plastigauge 'em; if they pass it should be fine.

I would highly recommend lapping the valves and replacing the valve stem seals in the "new" head.

 

BigFitz,

Thanks for the advice. This is the first time I am getting into any kind of engine work. It is good to know that what I thought would make sense, actually makes sense.

If there is anyone out there that has attempted to put Seca cams on a Maxim head, I would live to hear from you.

 

Last week, I finally got the engine completely back together. After fixing a couple of minor problems (a small oil leak from the valve cover and a major vacuum leak from a carb intake boot) the bike is running great!

So if anyone else out there has to replace a Seca head, you can use a Maxim head with Seca cams.