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Message started by t. dupree on 04/20/05 at 20:47:07

Title: Engine Rebuild (bad head)
Post by t. dupree on 04/20/05 at 20:47:07

http://www.picturefuse.com/picdetail.php?picid=42906

The link above is a pic of the camshaft bearing on my 1987 650cc (looking through the valve adjuster access plate). As you can see, the bearing surface is gouged an metal is shaving off the journal. The book says that the head must be replaced if it is out of spec. I can assume that the crankshaft is worn also because the engine knocks like crazy. This bike was GIVEN to me, so I don’t have any $$ invested in it yet. Everything else on the bike seems fine except for broken turn signals.
My questions are; Can this head be rebuilt or is it scrap like the book says? If it can be fixed, will it be cheaper to get a new/used head verses trying to repair this one? Where can I get engine overhaul parts? Do they make oversized crank and camshafts?

Thanks, tom

Title: Re: Engine Rebuild (bad head)
Post by slavy on 04/20/05 at 23:26:11

It is hard to see the condition of the head from the picture.
If You are asking a dealer- You need all new head with everything inside new.
If the question is "what would I do?"- new rocker arms, may be new cam chain,new cam if I feel like a big spender /I'd recommend this to You / , or if not- just use 500 and after that 1000 grit sand paper to round and smoothen the damages of the cam, change the valve seals and put everything back together.

Title: Re: Engine Rebuild (bad head)
Post by WD on 04/20/05 at 23:58:29

If you can afford it, just throw on a replacement. Rebuild your old one to see if you can. That way, if your rebuild efforts work, you have a spare head assembly in case you need one again.

With the discoloration and galling in that photo, that bike either ran out of oil or was run using too light a grade of oil. Or both. When you fix it, switch to 20W50. Works better in the heat, and in several bikes now, lets the clutch work smoother.

Any competent automotive machine shop can likely save the head and cam. Maybe even the rockers. Have them put in new valve guides, get the valve seats clean up ground, the valves lapped (if you don't know how, although it's pretty easy). Buy a new cam chain, head gasket, etc.
-WD

Title: Re: Engine Rebuild (bad head)
Post by Greg_650 on 04/22/05 at 09:43:03

t. dupree wrote:

Tom,

The camshaft runs in "plain bearings" in the head and headcover, and if there is damage to those, you'll have to replace both parts. I've never heard of oversize parts and cannot image how any regular machine shop could rebore the journals either. I do believe that you can have the cam reground if you decide to do that, though.

Now, I've studied this photo and compared it to ones that I've taken. (I'm about cross-eyed now, too). Is this looking through the intake valves? And what we see is the intake lobe on the camshaft? I see the scrapes on part of the bearing surface too, but that particular area is not under the headcover. The worst part about any scrapes is a loss of oil pressure....

I'd pull the headcover for a closer look before deciding....

Now, about the knocking sound in the bottom end. Can you tell where it comes from?

Title: Re: Engine Rebuild (bad head)
Post by lancer on 04/22/05 at 14:30:21

The cam can be reground for sure, had mine done by Webcams in California...a performance grind of course. "Try it, you'll like it". I had some slight damage in the so-called "cam bearing". On my '96 there are no actual bearings, just the milled aluminum of the head material that the cam sits in...cam directly on the aluminum. Kind of makes lubrication essential. Even if the bearing area of the head is damaged I would think that a machine shop would be able to come up with some real bronze plain bearings of the correct size and machine the head to accept them. That would be better anyway.

Title: Re: Engine Rebuild (bad head)
Post by Savage_Rob on 04/22/05 at 17:50:35

I am amazed that this thread has gone this long with no comment from Sluggo stating there's no such thing.

Title: Re: Engine Rebuild (bad head)
Post by bobo383 on 04/23/05 at 05:39:06

Savage_Rob wrote:

I am amazed that this thread has gone this long with no comment from Sluggo stating there's no such thing.

darn, that's funny. I just got it. Have to agree with sluggo if he said that.

Title: Re: Engine Rebuild (bad head)
Post by Greg_650 on 04/23/05 at 07:11:47

lancer wrote:

Sure, line boring the cam journals could be done, and bronze inserts would certainly beef up the camshaft, but I just have a feeling that machine shop costs would be prohibitive compared to buying a used head/head cover. I could be wrong.... :D

Title: Re: Engine Rebuild (bad head)
Post by lancer on 04/23/05 at 09:16:41

I am not sure of the cost of a new head but it seems like it is in the $4-500 range. A used one would be much more affordable. In this part of the country a machine shop would do this kind of work for about a $100.

Title: Re: Engine Rebuild (bad head)
Post by woodworker on 04/23/05 at 15:05:36

t. dupree wrote:

Tom;
Have you bothered to check the oil clearances between the camshaft journals and head/head cover journals?
If they are under .006" they are within limits.

Title: Re: Engine Rebuild (bad head)
Post by sluggo on 04/23/05 at 15:23:11

Savage_Rob wrote:

I am amazed that this thread has gone this long with no comment from Sluggo stating there's no such thing.

i was trying to show a little decorum, that and i just couldnt figgue out which way i wanted to go with it.

no bad head, just bad girls.

Title: Re: Engine Rebuild (bad head)
Post by t.dupree on 04/23/05 at 20:54:13

Thanks for all the comments
Sorry about the worn bearing confusion. I have always called them bearings because they are bearing surfaces (not ball or needle bearings)
One of the main reasons I posted was to see if this motor was even rebuildable with the initial damage I found looking through the valve cover. I figured if the motor was not repairable (cheaply) I might as well part the bike out instead of investing a lot of $$ and time in it. Reading everyone’s comments tells me that all is not lost and I will tear the motor down to see how bad it is. I will post my findings if anyone is interested, but it may be a few weeks before I get to it.
WD, I agree with your oil theory. Either too thin oil weight or intentional over revving caused this. The bike has 16,000 miles on it and the motor should have lasted longer than this with proper care. I believe the knocking is piston slap (piston pin worn) because it sounds pretty high in the motor. I’ll find out when I tear it down.
Greg_650, I also noticed that the scrapes are on the head and not the head cover. Also, the head cover does not support the camshaft directly above this location. It makes me wonder if the cam is even supposed to be touching the head at this location. If not, the cam journals must be way over the .006” that Woodworker says they should be.
And finally, it took me a while to figure out what Savage_Rob and bobo383 were talking about (I’m a newbie to the forum) but I have to agree with Sluggo as long as there’s a woman actively involved.
Again thanks, TOM

Title: Re: Engine Rebuild (bad head)
Post by bobo383 on 04/23/05 at 21:12:29

Tom, my Savage has scarred cam bearing surfaces, too. Mine came from gas in the crankcase, before I got it. It makes a little racket now but the bike runs like a scalded ape so I can't really complain.

If you have an old Ford (any old car for that matter) , you've learned to live with the sound of a sack full of cats coming from the motor. It's OK.