Triumphrat

delrazor · 08-07-2009, 12:11 AM

For those not familiar with my other thread, I am disassembling my motor (t120rv) to see what condition the crank bearings are in.

I have the head and barrel off and so far all looks good.
I filled the chambers with fuel and they held it in, making me wonder if I could avoid a valve grind and just replace the guides. Another part of me says "send it away and start fresh". Unfortunately that part of me doesn't have to feed a family. I have one helicoil required (small rocker cover bolt) and perhaps the spark plug threads. They wobble right up until they are nipped up.

Anyway the question is.... if I go with a generic (yet legendary) head place, what parts should I definitely send along with it?

cheers

derek

RetroRod · 08-07-2009, 03:50 AM

Derek,

I recall from a past post that you recorded very good compression with this motor 185psi +/- 5. That indicates you have a good seal on valves and rings.

I'm not sure what prompts you to considering the replacement of the valve guides, as from memory you have no symptoms related to these.

If the hip pocket nerve is sensitive, then I'd let sleeping dogs lie. If it ain't broke, don't fix it. Just clean up the head (decarbon) and back on it goes with the original copper gasket which you will anneal.

I guess the next thing to do with the bore is to determine how much wear you have in the middle, relative to the top and skirt. If its within reasonable limits, give it a slight hone and reassemble with original pistons and rings. RR

delrazor · 08-07-2009, 04:19 AM

Rod, The guides were letting in oil to the chambers about 4ml /mile.

I have found a crack in the head. The top of where the centrebolt goes in is split down about an inch. It definitely doesn't carry on down to the chamber. I wonder if it is common. No doubt it has been over-torqued at some stage.

This kind of thing makes me lean towards a complete rebuild.

derek

epynt1050 · 08-07-2009, 04:29 AM

If you change the guides, you will need to recut the seats and grind in the valves but both jobs can be DIY. You will just need the right cutters, grinding tool and paste. Not wildly expensive, certainly cheaper than sending the head away.
Would also gas flow the head whilst I was at it. Again DIY. Just need some small grinding wheels/heads and a small flexible drive from an electrical drill.

Skidemon44 · 08-07-2009, 05:27 AM

I'd check your exhaust spigotts, if they are loose in the head, get them replaced when you have the head work done. Headworks in Murrumbeena did mine and they do excellent work.

RetroRod · 08-07-2009, 05:43 AM

Quote:

Originally Posted by delrazor

Rod, The guides were letting in oil to the chambers about 4ml /mile.....................
derek

Derek,

I'm curious about how you know that the guides were "letting in oil to the chambers about 4ml /mile" Oil injected into the motor this way is usually sucked down the valve guides by high vacuum in the chamber under decelleration.

It is seen often enough in vehicles that have slowed for the stop lights, idled awhile, and then let go this huge cloud of blue smoke at take off that quickly subsides under accelleration. Oil usage from this would be high around town and virtually nil on the highway (did you notice, or have you been told about similar symptoms on this engine?).

So, with oil consumption running at 6.66 pints/1000miles (very excessive: and I wonder if this much oil could make its way down the valve guide), you just need to be certain its coming from the head, or your limited resources will not be well spent.

The Triumph motor does not have lots of oil around the valve guides as it returns quickly to the sump via oil valley in the head and the push rod tubes (PRT). On a budget, it would be cheaper to fit a cap type valve stem seal than to go the full nine yards with a reconditioning of the head.

The above comments assume the guides are tight in the head and have not loosened, which if the case, excessive oil would enter the chamber this way

The crack may well be left alone. Remember if it is repaired properly, the preparation and welding will require that the head be refaced and that could bring your way another can of worms. Not having seen the head, one cannot say one way or the other, but looking at the thing as a whole: you've had v.good compression on this engine so clearly the crack is not a problem now, and may never be.

It is never easy to make decisions when, on one hand, a full and good repair of everything is horribly expensive, and on the other, the conflict of limited resources. Engines generally do not respond well to being half done up. In your case it may be a case of spending as little as possible (ie, rebuild with existing parts), or go for broke and do everything from the ground up with new gear ( ie, reconditioned top end and repairs to whatever you find in the crankcase). Not always an easy call Derek. RR

delrazor · 08-07-2009, 08:34 AM

Rod, thanks for getting on board here. I appreciate it. The oil thing was a guess based on what falls out and what was missing after 800 miles (ish).
Since having this bike I have found the most attrocious bodge work and have been hoping that the owner did his own 'body work' and sent the motor out. Since looking inside yesterday it is obvious that he also did the motor and I have accepted that a rebuild top and bottom are the only way to confidently enjoy riding without waiting for something diabolical to happen ruining the cases forever.

I'll send the head to headworks and cop it sweet. This way I can get stuck into the bottom end. Do you think they will supply the parts needed or should I place a big order?

Two quick notes before focussing on the footy:
the head looks to have been skimmed at some stage. The gasket surface is raised at one side and blends straight into the fin at the other. Normal?

There was blue goo around the valve guides in the head (in the rocker area). I am scared this means the guide holes are sloppy.

cheers
derek

delrazor · 08-08-2009, 05:57 AM

sometimes in life you just have to make a stand.

RetroRod · 08-08-2009, 06:25 AM

Quote:

Originally Posted by delrazor

......the head looks to have been skimmed at some stage. The gasket surface is raised at one side and blends straight into the fin at the other. Normal?

The answer is no. The surface may be flat, but not level.

With respect to sending the head away for repairs. Skidemonn44 used "Headworks in Murrumbeena" and was happy with the work. If you plan to use the same firm they may well have access to all the parts they need to recondition the head. Alternatively you may ask them to disassemble the head and list the items they need to do the repair, then you can resource these from your favourite trump supplier.

If it were mine, and given you seem to want to go whole hog on this rebuild, get the crack welded and the head faced, AND LEVELLED. It seems to me that this will leave the head facing level with the fins and thus a long way thinner than original.

This then leads to setting up this head to achieve the correct "crush" (.055" to.060") on the PRT seals. IMHO you will need to go to an OS head gasket to get back some of the thickness reduced by the head repairs. This will have to be carefully checked on reassembly to ensure the PRTs do not leak.

Nice frame you've built there!!

Good luck. RR

GrandPaulZ · 08-08-2009, 11:45 AM

If have personally inspected nearly 100 Triumph twin heads, and have yet to see one that had the entire symetrical cylinder mating surface standing proud of the surrounding fin casting. they are typically a bit proud on 3/4 of the surface with one or the other side's rear fin section "blending in" to a degree, including a pointed casting that is obviously ground in the rough stage.

View photos of people's heads on-line and you'll find that to be the rule.