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Is this head a goner?
#810019 05/23/20 6:26 pm
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Cory Offline OP
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Howdy all, been a while. Today I pulled the head off a Bonneville engine(69), and found the recess where the exhaust pushrod tube seats in the head pretty mangled. I've taken pictures from the top and bottom sides. I'm not sure if this can be repaired, I'm thinking if it's possible or worthwhile doing it'll take some tig welding and machining by somebody competent.

And again on the exhaust side, the rocker box bolts on top were too large. I'll have to buy the right helicoil kit or uni-thread if they're British threads, can't remember offhand, I'll look it up. But everything else looks great, and the motor had good compression. What do you guys think?

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Re: Is this head a goner?
Cory #810028 05/23/20 7:38 pm
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Hi Cory, What is that in the PRT bores? Looks like epoxy?? I can't tell. What do you get if you crack all that out? I don't see how oil would drain with out puddling as it would have blocked top of PRT drain slots/holes.

From your photo I can't tell if you have deep PRT bore for later Wedding band PRT. Is that drilled out? I'd start by cleaning all the old repair out & see what you have left.

I have detailed close of photo of correct original '69 Bonne head top of PRT on inside. Couldn't find one of outside. PM me your email & I can send it.

Regarding the rocker box bolt holes, if head is '69 the thread is unified 1/4-20. If drilled oversized, & threads are good, you may want to leave it as is.

I've helicoiled several of these. I always use drill press for helicoil tap drill. Then put tap in chuck & turn chuck by hand feeding it down most gently until tap is very deeply started. Most important it's very straight, or rocker box bolts will be crooked & won't line up right. Then you'll be filing out rocker box holes....

Remember, tip of helicoil must be 1.5-20 full threads below surface.

If oversize thread is damaged I'd have to see how much metal is left for sleeve insert. Underscores how important it is to be very thoughtful during repairs to cylinder heads. We get one shot to get it right.


1973 Tiger 750
Re: Is this head a goner?
TR7RVMan #810041 05/23/20 9:20 pm
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some flea-bay pics for comparison
[Linked Image from i.ebayimg.com]
[Linked Image from i.ebayimg.com]

was the tube glued in place ?

Re: Is this head a goner?
TR7RVMan #810046 05/23/20 10:39 pm
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Cory Offline OP
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I think the black stuff in there was some type of sealant, I cleaned it up as best I could but it's pretty stubborn. The ring in the head where the tube and o-ring seat, there's chunks of that metal missing. Hopefully the pictures with it cleaned up will give you a better idea. Everything looks the same as the head quinten posted pictures of except mine has that ring partially broken off.

As far as the rocker box threads go, I took a rocker box bolt off another engine and tried the intake side, threads are just fine. But on the exhaust side, they didn't grab the properly sized bolt when I still had the boxes in place. There aren't any inserts in it either, that should be pretty straight forward to put a helicoil into if I'm careful.

I'm just concerned I won't be able to get a good seal on the exhaust side pushrod tube with chunks of the band missing. I'm thinking the oil will just flow around it because the o-ring can't seat properly if all the metal isn't there to hold it in place.

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Re: Is this head a goner?
Cory #810064 05/24/20 1:23 am
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Hi Cory, I'd like to see how the PRT fits into head with the upper O-ring. If there is enough metal there, to keep o-ring from riding up, you have a reasonable chance to get sealing. This is... If you use silicon. Such as Suzuki bond. I'll get part # later. I'd use the silicon on both top & bottom round O-rings in this case. Welding & machining is real repair. Remember the PRT goes at an angle to the head & rocker box surfaces. So have machine shop keep that in mind. I've research the angle. There is a good YouTube video where a fellow modified his head. Shows his set up. Really smart guy.

I'd have to practice on old head, but would Muggy Weld aluminum brazing work? Then machine down. YouTube makes it look viable. But... I've never used it. For sure good flux is key though. As well as correct heat.

I wonder how head got damaged? Maybe they had incorrect tappet blocks or PRT?? Then forced it?? I'd have go back & study the sealing combinations. That thought might not even be possible.

Would it be worth to get estimate for proper weld & machine? I have no idea where that could be done.
Don


1973 Tiger 750
Re: Is this head a goner?
TR7RVMan #810068 05/24/20 2:31 am
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Hey TR7RVMan, I'll get a picture tomorrow with the tube in place. I don't recall the o-ring being torn up or anything, but I kept it and will have a look. I'll look for that video as well.

Years ago I had a primary cover with the smallest crack in it I wanted a small weld in just so oil couldn't leak out, nobody in my city would touch it just because it was aluminum. But I can ask around again. Unfortunately I'm not allowed to weld since I have a pacemaker now, but I never learned how before I had it put in anyway. I do know some welders, one in particular that was getting into TIG welding, I'm sure if there's anyone around that can do it, she'll know who.

As far as how it got damaged, kind of a head scratcher at the moment. The seal at the tappet block wasn't the largest one, I'll pull those off and see what size are on there.But they were in pretty good shape, so I'm doubting that was the culprit. Wish I would've checked the gap before taking everything off, but I didn't even notice anything was amiss until I pulled the head off the barrels.

I used to have a great mechanic here, he'd been working on these bikes since '62, he owned a shop and he's since retired, and his son runs it now A good resource if I was in a pinch. I've traded some labor for parts with him, might be worth seeing if he'd have a look. He was and might still be doing restorations. There is another shop here that works on American and British motorcycles too, might be worth asking them to have a look as well. Who knows, a different head might be the cheaper option here.

Re: Is this head a goner?
Cory #810072 05/24/20 3:33 am
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...I also see that the base (surface) gasket is kind of recessed between the chambers?

Re: Is this head a goner?
Cory #810077 05/24/20 3:50 am
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http://vintagebikemagazine.com/technical-articles/push-rod-tubes/
Try to figure out why this damage occurred. If all the parts and the crush is correct then put it back together with a big gob of this;
https://www.fagengine.com/collections/hylomar-products
If it dosn't leak your home almost free.


1968 T120R
1972 T120RV
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Re: Is this head a goner?
Cory #810103 05/24/20 1:14 pm
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Do you have a light aircraft company (or similar) close by? One near me has a couple really accomplished welders that I call on for aluminum and stainless welding, good to have friends there. Just a thought... Otoh, a local fab shop that I used to weld some stainless exhaust pipes kinda made a mess of it ($). Wish I'd used my friend at the aircraft company (no$).


'68 Bonnie, '70 TR6r
'74 CL360
trail 70's and minitrails
Re: Is this head a goner?
Cory #810109 05/24/20 2:54 pm
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Welding down into that hole is going to be extremely difficult even for an accomplished welder. This might be better to do do with a wire fed MIG welder. Cast aluminum has alloying elements which can also make it more difficult (but not impossible) to weld. It will also be vital to get all contaminants, including oil, from the weld and surrounding area. Probably best to heat the entire head before welding. It is not a job for beginners. Then it will require machining, which will be a difficult set up. All of that will make it pricey. And that's if you can find somebody to do it without screwing it up.

Re: Is this head a goner?
Cory #810115 05/24/20 3:33 pm
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Not knowing anything about these heads, but could you not use a cutter to make the whole area clean and round, then put a sleeve on of interference fit, weld it into place on the top side and cut it back enough until you have the right clearance for the rockers etc??


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Re: Is this head a goner?
Cory #810122 05/24/20 4:22 pm
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Hi Allan, Hmm.... That is an outstanding idea!!
I’d have to have head in hand to see how much metal you have to work with. That is a very practical solution.

Make sleeve to replicate original bore.
Light press fit & sleeve retainer liquid.

I custom made stepped aluminum wedding band for my bike that had undersized PRT. Worked good. Sleeves can be thin & stool be strong.

Nice thing about forum is spring boarding ideas. Together we are better!
Don


1973 Tiger 750
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Re: Is this head a goner?
Cory #810126 05/24/20 4:42 pm
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Cory to me it looks like a job for Jake Hall, Asheville, NC PM me and I will give you his email and phone number. If you find someone else to weld/machine or sleeve the head, the angle of the tube is 3.3° When I was younger I loved those jobs. Then my welder, who seemed to be able to weld aluminum submerged in oil, left us.

Re: Is this head a goner?
Cory #810128 05/24/20 4:52 pm
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Rather than trying to weld, I would bore the O.D. of the seal area through then take the small step before the seal area down to 0.025" past the original step. Machine a steel ring and press it in with sealer. You could always weld later if needed but you take less chance of warping the head with a pressed in sleeve.

Re: Is this head a goner?
Cory #810130 05/24/20 5:08 pm
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You need more than a good welder. You need someone who makes a living working on British bike heads. Try John's suggestion or these guys. They did some beautiful work on my 68 head.
https://www.shopevengineering.com/services


1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.
Re: Is this head a goner?
Cory #810138 05/24/20 5:50 pm
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On my pre-unit 650 the upper PRT seal abuts the lowest rebate shown in the 3rd and 4th pics.
The flange toward the top of the PRT, and the squished white seal, are clearly visible looking from below. The flange is about level with the lower surface of the head.
The uppermost ID of the head serves to centralize the extended upper length of the PRT, such that the seal areas are accurately located.
The actual sealing is done at the lowest rebate surface.
The 2nd rebate is to allow the sealing ring to squish inwards and upwards against the upper extension of the PRT. Otherwise, it would have no option but to uselessly squish outwards.

I don't know if the later units differ radically from this design, I am doubtful. I suspect the main differences were of minor dimensions and profile, to accommodate different upper sealing rings.

I'm doubtful the sealing surface was ever raised to the highest rebate surface (the broken one). If it were, what would be the point of machining the lowest rebate?

I'd suggest trying your PRT's, see where their flanges abut the head, that will tell you where the seal surface is.
It may be that the damage is inconsequential (however it may have been caused) as long as the upper end of the PRT and seal is located correctly in its rebate.

Best of.

Re: Is this head a goner?
DMadigan #810144 05/24/20 6:17 pm
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Originally Posted by DMadigan
Rather than trying to weld, I would bore the O.D. of the seal area through then take the small step before the seal area down to 0.025" past the original step. Machine a steel ring and press it in with sealer. You could always weld later if needed but you take less chance of warping the head with a pressed in sleeve.

Wasnt thinking pressed in, it’s a good way of scoring the two pieces. Was thinking more heated head and frozen sleeve.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Re: Is this head a goner?
Cory #810147 05/24/20 6:34 pm
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Hi, As I understand it, ‘69 was the first year of “improved” PRT sealing. Head is bored such oring enters bore & seals on sides as well as top.
Head, tasppet blocks, PRT all have to match. This is when wedding band started & the white soft bottom seal wedding band contains.
Also used on T140 with shorter PRT.
Later T140 did away with bottom square seal. This motor used different tappet blocks & PRT but keeps wedding band. The way I see it weeding band is cosmetic in this case.
Don


1973 Tiger 750
Re: Is this head a goner?
Cory #810149 05/24/20 7:08 pm
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Don TR7RV"Hi, As I understand it, ‘69 was the first year of “improved” PRT sealing. Head is bored such oring enters bore & seals on sides as well as top."

Don, I hear you, but did they move the sealing surfaces of the interface between PRT flange and head all the way to that top broken head flange? This is what I am doubting.

Do you have a spare head and tube to see where the sealing region is?
My doubt is that the broken area is not the sealing area. As I described, that ring on early models was only to locate the upper extention of the PRT, the sealing was done lower down.

Say on your TR7, do the PRT flanges disappear way up into the recess of the head?

Cheers.

Re: Is this head a goner?
Cory #810162 05/24/20 8:27 pm
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The bottom of broken surface is integral part of where the O ring seals. It will have to be dealt with if this head is going to be used. Yes Ed at E&V is qualified to do this job. Owning welding equipment doesn't make you a welder. Jake Hall takes one of these heads, remove guides and valve seats, welds the ports, guide holes and combustion chamber up solid. Then machines the lot, cutting a squish band, putting in bronze seats to run Titanium valves and then raises the ports which he welded solid. Ed is capable of the same kind of work. These heads have been welded successfully since the day they were first introduced.

There is very little space to put in an appropriate sleeve, whether it be pressed or welded in place.

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Re: Is this head a goner?
Cory #810177 05/24/20 9:25 pm
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Thanks John.
I am surprised that later PRT flanges go that far into the head.
I live and learn!
Cheers

Re: Is this head a goner?
Cory #810271 05/25/20 7:41 pm
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When I said "pressed in" I meant interference fit, not pressed in cold.
The seal area on this parallel port head appears to be the part that is broken on your head.
[Linked Image from live.staticflickr.com]
There is a lead-in chamfer and the step were the seal seals against.The seal could be against the diameter but since the pushrod tubes are captured on the ends, I think sealing against the flat is more reliable.
Even with the lead-in chamfer a square seal is difficult to get in without rolling the edge over. A round O-ring goes in easier and still contacts both the flat and diameter. A #120 O-ring is 3/32", 1" I.D., 1.193" O.D. will fit with interference both I.D. and O.D.
I had to reduce the O.D. of my adjustable PRTs to fit into the recess, 1.162" seems to be the maximum.
On your head a small ring can be put in with an interference fit and sealer which sits on the current seal area. A stepped ring is not needed.
Adjusting for the shortened length is not a problem.
[Linked Image from live.staticflickr.com]
Not marked well but the area pointed to in red needs to be machined round for a ring to be fitted.
[Linked Image from live.staticflickr.com]

Last edited by DMadigan; 05/25/20 7:51 pm.
Re: Is this head a goner?
Cory #810281 05/25/20 9:07 pm
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Seems a good possible solution from DMadigan. May need his adjustable PRT though.

I would only observe that what I describe as the first rebate in the head doesn't look like a lead-in chamfer, it looks like a machined flat surface. If that is true, what is it for?

Re: Is this head a goner?
Cory #810291 05/25/20 10:55 pm
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Please Let us know what the final fix is

Re: Is this head a goner?
Cory #810304 05/26/20 12:49 am
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Hi Cory, John Healy has recommended a known good source of repair. Smart money demands send him photos of your head & get his thoughts & possible estimate. Safe bet always gives good results. It just does. Gambles leaves you loosing both money & a non usable head.

As I said recently, easier to find a gold nugget than a good used head. Key word is good.

Would be interesting to know if new LF Harris made heads are any good?? I'd fix my old one in a heart beat if CV can fix it.
Don


1973 Tiger 750
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