XS motor winter rebuild!

[blackbetty]

So I took the XS out for a spin on Tuesday, came home and noticed the motor was hemorrhaging oil out the base gasket and cam oiler tube. I'm glad I got home when I did, because when I drained the oil, it was nearly at half capacity

I had been planning on just getting a valve job to cure some leaking valve stem seals, but after thinking about it and salvaging a few more weeks out of the season, I've decided to step it up a bit more.

I spoke to Roger at Hoos Racing and I'll be sending my jugs/head to him for machine work. Going to get a 3 angle valve job, a 700 kit, a Shell #1 cam, and HI-PO valve springs. Will do the preventative stuff too, cam chain, guides. I'm also upgrading to the '81 clutch.

I'll get the engine pulled apart this weekend and document the rebuild for anyone interested. I've decided not to rephase my XS engine.

Here she is pre-op next to the 77 I-6 3-on-the-tree:

Stay tuned, and if anyone else has any suggestions, let me know! I'll be keeping the Boyer ignition and my 76-77 BS38s.

 

[CoastsideXS650]

If you're going to all that trouble you should invest the extra couple of hundred dollars and do a rephase. You are going to want an electronic ignition anyway. You will love the result.

 

[pregrid]

Sub'd..................

 

[blackbetty]

If you're going to all that trouble you should invest the extra couple of hundred dollars and do a rephase. You are going to want an electronic ignition anyway. You will love the result.

There's a lot of people who champion the rephase for the XS, but I'm not sold. The stock vibes don't bug me, I don't really flog my bike over 7K rpm, and you're not adding any more displacement. I appreciate the added insurance of welded crank pins, but to spend $1000 all said and done on a rephased crank and a new ignition for no real gains doesn't make sense to me. I've already got a new Boyer Micro Power on the bike now and I really like it.

With the 700 kit I can get 9.5:1 with a base gasket; that should be plenty strong for my needs.

 

[CDNTX650]

i agree, the awesomeness of this motor is 360* crank. Id rather 750. Hell with tall gearing and stock 650 rebuilt, you hardly need to go past 6000rpm and it's movin pretty good.

 

[Ironsled77]

Ill be joining you in the rebuild this winter! It will be my first so keep it documented!.


Everyone seems to think a rephase is a couple hunderd bucks...its not, I would love to do it but I cant shell out the 1000+ bucks when I have WAY more in to the bike than I could ever get out

 

[blackbetty]

Ill be joining you in the rebuild this winter! It will be my first so keep it documented!.


Everyone seems to think a rephase is a couple hunderd bucks...its not, I would love to do it but I cant shell out the 1000+ bucks when I have WAY more in to the bike than I could ever get out

Hell yea man! Any mods or just doing a straight rebuild?

I just ordered a clutch off an '81 from joe wiseguy. I'm about to head out to the garage to get started, I'm interested to see what the inside of my engine is looking like. I'll post pics later.

CDNTX, I like the 750 as well, but with the 700 I'm spending $375 for pistons/rings and I can just bore the stock sleeve for $40 a hole. Not too bad, and helps keep the engine stock looking. I do appreciate those big 750 jugs though.

 

[racerdave]

Doe's going to 700 leave enough liner for good heat tranfer for cooling? Are there any oversize's left after 700? Is it actually 700 cc or 680ish?

HP gain is not a concern, but is there any bottom/midrange torque gain?

 

[Ironsled77]

Well it had a base gasket leak also. I will probaly end up doing the exact same thing you are. Plus I need to tear it down for paint. Even more money! But im gonna do it all myself so we shall see what the price is....

 

[JimR]

Hell yea man! Any mods or just doing a straight rebuild?

I just ordered a clutch off an '81 from joe wiseguy. I'm about to head out to the garage to get started, I'm interested to see what the inside of my engine is looking like. I'll post pics later.

CDNTX, I like the 750 as well, but with the 700 I'm spending $375 for pistons/rings and I can just bore the stock sleeve for $40 a hole. Not too bad, and helps keep the engine stock looking. I do appreciate those big 750 jugs though.

I like big juggs too..
You said you dont thrash over 7000 rpm. The Shell #1 cam is a short track race cam.
I'm not sure of the power band, but I'm thinkin it's going to have plenty of lungs left at 7000. I'm curious cuz that is the exact same setup I am considering. Did they mention operating range ?

Jim

 

[yamaman]

CDNTX, I like the 750 as well, but with the 700 I'm spending $375 for pistons/rings and I can just bore the stock sleeve for $40 a hole. Not too bad, and helps keep the engine stock looking. I do appreciate those big 750 jugs though.

im not sure that you'll get your boring done for $80, that would be per pass. those pistons are 77.5mm correct? check with your machinest, that might need up to 4 passes. The 750 kit is looking a bit cheaper then. Goodluck with whichever way you go. cheers

Posted via Mobile

 

[jobagadonitz]

Yeah, I'm doing basically the same thing for the same reason. spewing oil. For me it's out of the head gasket, oil tube and various other sources. I'm thinking of the 750 kit also. Everything else stock with the exception of the Commando pipes from Mikes.

I've read that the 750 kit is a true bolt-on upgrade. but others have said you should also upgrade the cam. I'm not looking for a screamer. Just some good performance at highway speeds with some oomph left over to get myself out of trouble. So what is the general consensus here?

 

[blackbetty]

I got my motor pulled down this weekend, and overall, I'm not surprised with how everything came out. I discovered the head gasket was leaking bad, and as previously mentioned, the base gasket was oozing from the front. Cylinder walls were in good shape with no scratches or pits, but there was some slight discoloration on the right cylinder.

I also found that the right cylinder exhaust rocker had some bind towards the end of it's range of motion. You can also see that the exhaust valve on this cylinder is nice and crispy. This was probably the source of some strange head noise I would experience a little higher up in the RPM range. Camshaft lobes look OK.

The cam chain guides looked almost new, I wonder if someone has been in here before:

Left cylinder:

Right cylinder:

 

[blackbetty]

SO now that it's all pulled apart, I'm back to the drawing board with the 700 vs the 750.

I can get a cool stock looking 700cc with a Shell #1 at 10.5:1. I think a motor like this on a street bike would be fun as hell.

OR I could go with the 750 kit. If I went 750 I'd stick with the factory cam and then just have Hoos refurbish my head.

I'm going to do more research on 700 vs 750, definitely all ears to your suggestions.

 

[yamaman]

dwyatt has made his a 700, i know he's happy with it. search for his posts for more info. also, as i posted earlier, check your boring costs again, $40 per pot or $40 per pass. could make a big difference, .5mm to .75mm is as much as most borers can cut in 1 hit, and you will need 2.5mm cut, so that could get expensive! cheers

Posted via Mobile

 

[jefft]

Can you tell me about your hardtail. I like the looks of it. Where did you get it and the details, dimentions? Also, for those that have bought Mikes 750 kit, did the rings require any filing?
Jefft

 

[alfredo]

Subscribed. Hoping to rebuild some motors this snowy season as well.

 

[blackbetty]

Can you tell me about your hardtail. I like the looks of it. Where did you get it and the details, dimentions? Also, for those that have bought Mikes 750 kit, did the rings require any filing?
Jefft

Hardtail is the super common TCBros unit.

I spoke to Roger at Hoos and it looks like they'll do a $40 per cylinder up to 3mm, so the machine work on my jugs for the 700 kit will only be $80.

That being said, I've committed to the Hoos 700 kit/shell #1/RD valve springs and reconditioned head, and new cam chain and guides.

I'm shipping off my parts today and I'll post up when they arrive.

In the meantime, I'll be pulling my 75 clutch and swapping with an 81, and upgrading to heavier springs and new friction discs.

Stay tuned!

 

[alfredo]

In the meantime, I'll be pulling my 75 clutch and swapping with an 81, and upgrading to heavier springs and new friction discs.

Whats the difference in the clutch packs in those years?

 

[jobagadonitz]

I have been talking to Roger about the exact same thing. Question: why did you decide to go with the 700 kit and the cam rather than the 750? What were your pros and cons? I'm waffling back and forth. Can't decide. Roger says the 700 with the #1 cam will really wake up the mid-range acceleration. What would the 750 with the stock cam give me?