Top end rebuild, how far to go?

TheDude · Posted: June 24, 2008, 1:31 pm Post subject: Top end rebuild, how far to go?

OK, here’s the story. I’m in the middle of a move (to a place w/o a shop), so I need to work fast before I go. I pulled my top end apart bc I had the signs of a failing cam chain guide (plastic and metal shavings in the filter screen. Furthermore, I have some piston sealing issues (120 psi compression / 150 psi w/ oil in the cylinders). Here are my questions:

1. Cylinders, the barrels are within spec and relatively free from scoring. Do I slap ‘em back together, drop $80 on rings and hone, or go for Mike’s 750 kit (something I plan to do eventually anyway)?

2. head, Right now, the valves are sealing well. I can get no solvent to pass through them. Do I still need to pull them out and lap them? The combustion chamber looks pretty nasty (see photo). Is this normal?

The bike is a ‘78E w/ 30K mi. I have pod filters and I will be installing new pipes when I put it together. Any opinions would be greatly appreciated.

Thanks!!

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

Watching for solvent to leak by the valves really isn't the best test for leaks. It will only show really bad ones. You need to set the head upside down and level on the work bench, install some old plugs, fill the combustion chambers with solvent, then blow compressed air in the exhaust and intake ports. Leaking valves will show a stream of bubbles around the edges. The exhausts are the usual leakers.

Decarbonize the head and pistons. I use paint stripper. It pretty much melts the carbon off but may take a couple applications.

At 30K, I would replace the cam chain. Check the ring end gaps and replace if out of spec. I use 1st over size and file my own end gaps to the minimum spec, .008" I think.

weekendrider · Posted: June 24, 2008, 2:36 pm Post subject: Re: Top end rebuild, how far to go?

Anyone that cares to answer.
Looking at the back guide. Would you replace it?

TheDude · Posted: June 24, 2008, 3:01 pm Post subject: Re: Top end rebuild, how far to go?

yes, that was the original reason I took the photo. The grooves are about .020" deep. I was inclined to leave it.

weekendrider

I have the top end off one expecting to find plastic gone from the front.
But it's intact with no grooves, skid marks yes, but not grooved.The back is barely marked. So I was thinking bout leaving them till later.

xsjohn

Don't leave the front guide...replace it...bond to the aluminum and the plastic on the originals fail ....and quickly ...unless you just like taking it apart again.....and the front doesnt really groove ...think it was just 30 year old technology with the plastic and the bond ..just gives out.....the back seems to last forever unless someone tightened the chain to tight and trashed it........xsjohn

weekendrider

I'm beginning to wonder if it's the original. I was chasing a shoop shoop noise. After finding a couple of pieces of plastic wedged in the strainer vanes. Now that I have had it apart the front guide isn't missing any plastic?? I'm wondering if the noise was because the PO replaced them and swaped the washers on the head. Rubber to the inside and steel to the outside. Also when I removed the rockers the chain seemed to be off center so......

xsjohn · Posted: June 25, 2008, 1:15 am Post subject: Re: Top end rebuild, how far to go?

When in doubt change it out..........and hope for the best.......what are we talking 35 bucks or so......or maybe another dismantle....rings and all won't handle too many interuptions till it costs a bunch more to let someone rebore the whole mess and wonder what you have agan........and that crap gets into everything........xsjohn

jimmer · Posted: June 25, 2008, 5:18 pm Post subject: Re: Top end rebuild, how far to go?

If you want stock rings ... I have a new set of Hastings rings ... exact same as found here:
www.650motorcycles.com...Rings.html

I bought um (for a 4 cylinder) ... used 2 sets ... 2 new sets left. I don't want them. They are no good if you have honed 5 or 6 times over the years ( I had 27 thou end gap). You say you are within spec ... so they should fit. You want them ... yours free. PM me only if you think you can use them ... and if you can wait 2 weeks for shipping.

TheDude · Posted: June 25, 2008, 8:18 pm Post subject: Re: Top end rebuild, how far to go?

thanks Jimmer, I was debating on weather to buy rings, or spring for the XSPerforance 750cc kit. Upon further inspection I found that I was on the outside of the limit 2.953-2.955 (limit is 2.954), and my piston clearance was on the outside as well.

against my (and Michael Morse) better judgment , I ordered the 750 kit today.

TheDude · Posted: June 27, 2008, 3:32 pm Post subject: Re: Top end rebuild, how far to go?

I always let things snowball. Now that I have the 750 kit coming, I realized I had better pay someone to do a 3 angle valve job. I found a guy in town who just did the valve job, bead blasted and cleaned the head, and installed the valves and seals for $105. Now that was money well spent.

I needed a now cam chain and front guide as well. The chain was so sloppy that it was wearing on one side of the head and cylinders. I think I should have a solid top end now.

Now, to address that slipping clutch.

davmo · 650Rider Supporter Joined: Aug 21, 2006 Posts: 27

Hey Dude , What did MMM have against you ordering the 750 kit? Inquiring minds want to know. David

TheDude · Posted: June 27, 2008, 7:12 pm Post subject: Re: Top end rebuild, how far to go?

MMM did say the 750 kit is good quality and worth installing, but he feels it should be one of the last mods to be done. (my engine was stock except for pod filters)

I was originally trying to keep the mods and the rebuild to a minimum, and MMM was trying to advise me as to where my money would be best spent.

MM says that one should have an electronic ignition and headers (mike's XS or Mac) first off. a three angle valve job is the best thing one can do to make an XS run good.

He also recommended the crank be trued and welded prior to the 750 kit to handle the power.

I did the valve job, ordered some mack headpipes and some cheep Emgo mufflers off ebay. I don't have the time and money to split the case and have the crank work done. Plus I'm holding out on the ignition, cam, and crank until I decide if I want to do a rephase

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

I would do the solvent and compressed air test to see if that $105 really was money well spent.

TheDude · Posted: June 27, 2008, 9:34 pm Post subject: Re: Top end rebuild, how far to go?

So, you are suggesting I test to see how good a job he did? That's a good idea. I try that.
The machinist did say it needed the valve job due to some pitting on the seats. The engine has 31,000 mi. and is 30 years on it, so it was sure to be due for it.

one thing is that he is not a really motorcycle guy. he didn't have the 25 deg cutter speced in the manual, so he cut the inside angle to 30 deg. He also didn't have the radius cutter, and I am not sure what he did to compensate for that. However, he did come highly recommended (from a master mechanic friend of mine), so I am counting on it being a good job. It cirtainly will seal up better than the lapping job I was going to do.

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

Why spend a lot of money on an electronic ignition, Mikes single points cam lobe and duel output coil (some would prefer the coil to have detachable leads) and iridium plugs would do. luv those points........I have been talking to a guy here in AUS who has done a lot of rephase 750s and he swears the crank and berrings are more than strong enough to handle the 750. If the crank hasn't been apart before he then usually it will be ok to just press together again. weld it up there is no going back. Engines don't mind being wound out every now and then it is the over revving to often that will do the damage.........I hate these gauges of the other yamy's put on the 650 that red line past the 7.5 .........reading about a guy who was red lining at 9 thou......I shudder.

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

Welded cranks make me nervous just on principle, having driven a couple of trucks that had welded cranks in them.

And yes, I understand that MMM knows what he's talking about and that the welded cranks I had experience with weren't welded for the same reason you may have yours welded.

Still, welded cranks make me nervous just on principle. . . . Cool

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

This 3 angle valve job thing comes up from time to time. The fact is, these bikes come with one from the factory, you don't need to go out and get one. The only time there needs to be any cutting done on the angles leading into the seat is if lapping makes the seat too wide. I've lapped in some pretty badly pitted ones and the seat width was still in spec when I was done. Granted, cutting does take the pits out quicker but how many among us has a valve seat cutter sitting in their tool box?

I'm also fine with points. My bike is what I consider a budget ride (it was free). I replace and upgrade what needs to be. $300 for an ignition just isn't an acceptable expense for mine. Instead, I spent about $40 for the single points conversion (points cam, eBay coil, new plug wires and caps).

Joseph · Full Member Joined: May 22, 2007 Posts: 767 Location: NY

Thanks for clearing that up 5twins I was wondering about that.

gs1327 · 650Rider Supporter Joined: Feb 20, 2007 Posts: 170

jimmythetrucker-
You are correct-welded roller bearing cranks are welded for a different reason than plain bearing cranks- plain bearing cranks are welded as a repair, roller bearing cranks are welded at the pins to keep them from moving. Almost every dragbike you see with a roller bearing crank will have the pins welded so they can't move(big problem when launching with high horsepower and a slick). Welding is done even on a new crank before attempting to drag race it, to make it stronger-not as a repair to a damaged crank. Of course if the crank needs new rods or whatever the crank with the welded pins is not easily repaired, but companies such as APE, GRC, Falicon, etc. do it all the time. Anyone dragracing a GS1100 suzuki or KZ1000 kaw can tell you a crank that hasn't been welded will be history in no time.

TheDude

Well, I ain't doing any drag racing or anything close to it, and I have no intention of going into the bottom end anytime soon.

5twins, what you say about the 3 angle valve job makes sense. Considering that I don't really know what I'm doing and MMM does, I felt it would be a bad idea to ignore his advice on this one.

Especially considering the money I'm spending on parts. I, too many times, have shot myself in the foot because I "cheep out" when I shouldn't. Plus, I just made a killing on Ebay selling old RD400 and RZ350 parts I found while cleaning out my basement. This is money that is under the "wife radar" and must be spent on the bike.

I know an electronic ignition would be better, but I too have a hard time dropping $300 on an ignition when my points seem to be working perfectly.

xsjohn

I cheeped out on mine and just turned 57 thou and running as good as ever......still on the stock pistons..........THe exceptions being...2 crank disasters and a trans disaster and trashing the rings years ago from too big of a main jet ....cant cheep to much on these but cheep replacements are always welcomed......and if they are withing spec are probably as good as new......and have been pre tested......

xsjohn

Joseph · Full Member Joined: May 22, 2007 Posts: 767 Location: NY

650skull and anyone else, on a stock xs650 in your opinion is ok to hit the red line once in a while or go past it? I only ride for transportation and fun, hardly ever go above 5 but getting on pkwy on a clear sunday with no trafick i like to get it up to speed quik.

xsjohn · Posted: June 28, 2008, 1:15 pm Post subject: Re: Top end rebuild, how far to go?

My opinion the answer would be no.........above 5500 the bearings can slide and these pressed cranks have runouts less than perfect and crankshaft out of balance is greatly exaggerated at high rpms...........

There will be those who disagree of course.........

xsjohn

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