What did you do today? Cobba's rebuild

[Rod.s]

Well i did some of this with Cobba well he did most of it, actually nearly all of it

















Bad piston



Very bad pin



Very sad con rod



Bad design by Yamaha

[cobbadiggabuddyblooo]

Well the story begins.. Thanks to the time, patience and perserverence of Rod to help with each and every challenge I came across. Having the knowledge , tools and know how to get me through each stage. Over 2hrs spent trying to remove a snapped top sump bolt. Notching it and applying heat to no avail till we finally drilled it out as it had corroded into the sump and we couldn't remove it till drilled and sump removed . Then just a matter of unscrewing the remaining stud from the case itself. We also noticed the bottom end had been rebuilt previously and one small end on a rod had previously suffered due to lack of oil. I know I've put in 70,000km since I've owned the bike so a testament I would say to constant oil changes every 3 to 4000km to get the extra life from the motor. And as for the clutch , very little wear at all so any question of supercheap sale 10w40 oil affecting this.. Well the proof is in the pudding,, never had a clutch issue and still well near the top end of tollerence with another good 1000,000 km in it easy. But the further I pulled it apart the more and more silicone deposits I came across. Crank out tomorrow so I'm staying positive... But I need con rods so I know where my tax cheque is goin now..

[alextrx850]

Any lipping to the bores there Cobba ?

[cobbadiggabuddyblooo]

Bore looked pretty good and could still see most of the honing x hatching over most of the face. Some blow by marks appearing around the top of the piston. Evident especially this time in the oil colour and smell. All carbon deposits seemed old also with one plug running a little rich.. Crank day today coming up

[sanddune51]

Pleased that the pair of you are making such good progress on your motor overhaul . Hope no nasty surprises are lurking within.
Great photos too, keep 'em coming and good luck with the strip and rebuild.


Mark.

[QuickDraw]

Good we're all doing our rebuilds at the same time

Some familiar pics there. Just finished pulling my "spare" motor down last night. Looks like my bearings might be replacements too- not bad, but while it's apart I'd be mad not to renew them. Metallic particles in the oil seemed to have come from the small ends (and maybe cam journals/caps.. only mild scoring though. Cams ok thankfully) Considerable dark deposit on the sump floor. Bores and pistons are fine.

The spare motor will just be an honest budget stock rebuild so I'll use my good stock rods in this one, and maybe look at HC pistons and better rods for my "proper" mill. Keen for any suggestions on where to get good deal on those parts at good value.

Hey, has anyone got a good way of getting those B*%^*F$(*n T30 TORX screws out of the various shaft retainers?! I've buggered 2 bits and most of the screws from the balance shafts (having welded onto one to get it out!) Trying to get the gear cluster out without welding anything, but I'm at the point where I feel stupid even trying Has anyone had luck with an impact driver (before I waste my money)?

[Gordo]

I've buggered 2 bits and most of the screws from the balance shafts

Are they a quality moly bit or a regular repco/supacheap one?
I've had the same problem but not TRX related. Only other thing is make absolutely sure they are seated correctly & keep the bit straight on the bolt.

Gordo-

[davamb]

Think that bore might come up ok with a hone.

BTW, you're not related to Hunter S Thompson by any chance are you Cobba?

[QuickDraw]

Are they a quality moly bit or a regular repco/supacheap one?

First one was in a Kinchrome set. Second one was a $10 Repco job (came in a 3/8 socket). They both twisted. I ground the Repco one shorter and seated it better with a hammer, but that only helped with the Balance Shaft retainers. For the Gear Cluster retainers (punched screws), I put the casing on its side and had my full weight and a pipe on the handle of the drive ... nup. Wrecked the screw. Maybe Trade Tools at Nambour will have something.

[Rod.s]

Are they a quality moly bit or a regular repco/supacheap one?

First one was in a Kinchrome set. Second one was a $10 Repco job (came in a 3/8 socket). They both twisted. I ground the Repco one shorter and seated it better with a hammer, but that only helped with the Balance Shaft retainers. For the Gear Cluster retainers (punched screws), I put the casing on its side and had my full weight and a pipe on the handle of the drive ... nup. Wrecked the screw. Maybe Trade Tools at Nambour will have something.

Did you drill out the punch/locking marks first? Unless you have the screws are not going anywhere

[cobbadiggabuddyblooo]

That was how we could tell the bottom end had been rebuilt before.. Note it has been punched twice and one had been drilled to remove previously.
Thanks again Rod for the excellent photos and guidence on this rebuild. Back at TRX school and Removed the crank today and relieved to find it in excellent condition.
Once again having everything explained to me once pulled apart on what to look for and the how and why it is so. The wear on the bearing shells and what forces have caused the wear on certain parts of the shells. Then after a lubchbreak at the local patiserie a therory session for the arvo on the difference of design of the JE pistons and the standard yamaha , the pro's and cons of how they both work with flow of oil to cool the piston and lubricate the small end. The heat created with a higher compression piston and burn factors with fuel. With a conversation on the difference in cam profiles yesterday I feel so blessed to have the chance to take this rebuild onboard now. With my basic laymans teachings of what and why on motor components this have given me the understanding of the reasons behind this. Time to source a few more parts and engineering started before the cleaning ,oh did I mention more cleaning ,oh and yes the cleaning out of all the threads, I can see this preparation will take quite a number of hours.

[Rod.s]

It an't easy being this good looking, his words not mine......



Spares







Unless you drill out the punch mark the screws won't come out, that's what the punch mark is for.....



Two badly scored conrods, the galling is that deep it can be felt



Badly worn main bearing, what worries me is that the scratches don't start at the oil galley track! They are visible in the base steel right through to the unworn overlay plating, meaning that they were there PRIOR to being assembled These two scratches are consistent with someone using a screwdriver to remove the shell

You can see the four layers of the fluid bearing (Slipper bearing to some) base steel, first plating layer (like a primer for the nickel) nickel plating and the final (trade secrete) plated layer......babbit .......luckily i believe that the majority of the damage was done prior to Cobba buying the bike and his strict oil change regimes avoided an engine fail

Notice the white silicone gasket sealant on the top left of the shell



Evenly worn big end bearing The wear is where it should be as the crank applies pressure here on startup, this is what you should except from an engine that has high K's and is not an issue...yet



The crank is in very nice condition with no noticeable wear and the factory grinding marks still visible and even, got to be happy with that

Notice the "bluing" on the right of the main bearing. This bluing is on both sides of the camshaft chain sprocket as the sprocket is tempered (heated and cooled) to a different degree to the rest of the crankshaft and is done after the crank tempering.

[trixynut]

Interesting thread this, keep it coming.

Taking motors apart is good fun isn't it?

As an aside, that's an interesting bike Mr Thompson is astride. A Penton, small capacity MXers with Puch engines and KTM parts, built from 68 to 78.

Anyway, as you were.....

[alextrx850]

Interesting thread this, keep it coming.

Taking motors apart is good fun isn't it?

As an aside, that's an interesting bike Mr Thompson is astride. A Penton, small capacity MXers with Puch engines and KTM parts, built from 68 to 78.

Anyway, as you were.....

And an m16 in .223 cal, in a hunting stock..
Yep, as you were.

[QuickDraw]

Did you drill out the punch/locking marks first? Unless you have the screws are not going anywhere

Ah. No. I was thinking the punch was just a little anti-vibration measure- Thanks Rod!