Long time no type, Desmo conversion update

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jbcollier
Posts: 86
Joined: Sun Oct 10, 2010 2:30 am

Long time no type, Desmo conversion update

Postby jbcollier » Fri Apr 19, 2019 4:25 am

Been quite a few years, I’m sure, so it’s time to update you on my desmo adventures. I built up a cafe’d 250 single with a head ported by Syd’s and a full race cam from MegaCycle. The head was a small port, opened up for a 30 mm carb, larger valves and a coil spring conversion. Beautifully done and the engine ran sweetly all the way to 11K -- where budgetary concerns got the better of valour. All was good for a 1000 happy, hard miles. Then the valve guides were worn, not toast, but worn none-the-less. I guess what else can you expect with a full race cam and high revs?

Chance, ebay and a light head all came together one night when I ended up with a desmo head for $800. Even though complete desmo heads were then trading for $2000, it wasn’t quite the deal you might think. The seller -- AKA “the butcher” -- had decided to “race-port” it himself. Must have been a Texan because he liked wide-open spaces. So wide he went through the intake port into the valve spring area! Naturally all the rockers were shot as well...

So I cleaned the head carefully and sealed the intake port back up, and narrowed the port to match Syd’s porting (and added some drop), using Devcon Alloy putty. The seller had also hacked up the exhaust port so -- in for a penny, in for a pound -- I filled that as well. New seats, guides, rocker pins and bushings, valves, and full race cam from V2 and I was back in business. Inclination and necessity (the repaired area) had me run the head springless -- desmo singles usually use 160 valve springs.

Well, it all ran a treat. Seemed just as quick as the springer head though perhaps a tad more “tappet-ty” when the oil was hot. Several years and 2000 miles go by and I figure it’s time for a look-see. Off comes the head and I find the guides are like new, no play whatsoever. Both valves need one size larger closers (converted to twin closers so I could use valve seals), and the intake, one larger opener. No wear on the cam or rockers. The Devcon held up in both ports, yes in the exhaust as well! Tickled pink is what you would have to call me, that’s for sure.

Only one other thing to report. I use Penrite Classic Heavy oil (40-70). The bike had sat all winter before I pulled the head. The oil was still all over the cam and rockers, impressive.

Well, that’s it for now.

Cheers,

John

double diamond
Posts: 555
Joined: Thu Apr 28, 2011 1:20 am

Re: Long time no type, Desmo conversion update

Postby double diamond » Sat Apr 20, 2019 5:05 am

John,

Good information about using Devcon in the exhaust port. My WC 350 race bike currently has a Spanish head installed with some serious casting flaws in the exhaust port. Was thinking of filling with Devcon but wondered if it would hold up to the heat in the exhaust port. Sounds like it’s worth a try. Devcon has several products mixed with different base metals. Steel is the most commonly available but a product made with aluminum is also available. What Devcon product did you use?

Matt

Eldert
Posts: 771
Joined: Sun Nov 01, 2009 3:23 pm
Location: Hazerswoude Rijndijk Netherlands

Re: Long time no type, Desmo conversion update

Postby Eldert » Sat Apr 20, 2019 6:25 am

port filler

the stuff i use is Manley miracle seal epoxy 40180 .

from all the epoxy fillers this one can stand the highest temps .

Eldert

ducwiz
Posts: 604
Joined: Tue May 22, 2012 12:52 pm
Location: near Frankfurt, Germany

Re: Long time no type, Desmo conversion update

Postby ducwiz » Sat Apr 20, 2019 8:06 am

Eldert,

where did you buy this stuff? It is not anymore listed in the Manley catalog, and I couldn't find any supplier on the net.

cheers Hans

jbcollier
Posts: 86
Joined: Sun Oct 10, 2010 2:30 am

Re: Long time no type, Desmo conversion update

Postby jbcollier » Sat Apr 20, 2019 12:22 pm

I used just plain old Devcon Aluminum Putty, part # 10610 for a 1 lb container. It's basically a two part epoxy with aluminum filings in it. Frankly, I was surprised it worked on the exhaust side. Though not too surprised as it was recommended for the job by an two-stoke tuning friend of mine.

The most interesting thing for me was how much easier on the guides it is with the demo set-up.

Eldert
Posts: 771
Joined: Sun Nov 01, 2009 3:23 pm
Location: Hazerswoude Rijndijk Netherlands

Re: Long time no type, Desmo conversion update

Postby Eldert » Mon Apr 22, 2019 6:15 am

Hi Hans

looks like it is sold out everywhere . i will ask my supplier if he still has some left .

Eldert

ducwiz
Posts: 604
Joined: Tue May 22, 2012 12:52 pm
Location: near Frankfurt, Germany

Re: Long time no type, Desmo conversion update

Postby ducwiz » Mon Apr 22, 2019 2:19 pm

Thanks Eldert,

let's see.
Btw, surfing the net I just found JB Weld HighHeat epoxy putty https://www.jbweld.com/products/highheat-epoxy-putty. Seems to be a similar stuff, and is available from Amazon.de. What do you think?

Hans

Eldert
Posts: 771
Joined: Sun Nov 01, 2009 3:23 pm
Location: Hazerswoude Rijndijk Netherlands

Re: Long time no type, Desmo conversion update

Postby Eldert » Tue Apr 23, 2019 1:16 pm

Hi Hans
the JB looks good to me . the regular JB weld is great stuff to . you can even mix it with aceton
so you can pour the stuff to reach the hard to get to places . the open tube has a shelf life of 20 years .

Eldert

Bevel bob
Posts: 1043
Joined: Thu Apr 15, 2010 8:01 am
Location: Bromley Kent UK.

Re: Long time no type, Desmo conversion update

Postby Bevel bob » Tue Apr 23, 2019 2:36 pm

I have a head with the inlet valve boss removed and the likelihood that the guide will come loose again sooner or later. Was thinking of using Devcon to build up some support around the guide and maybe "D" shape the port floor a bit. Road use only. Seems a good idea?.


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