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The Vintage Japanese Motorcycle Owners Group: Discussion Forums

Vintage Japanese Motorcycle Owners Group :: View topic - Cold compression values, T20?


Cold compression values, T20?
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fodder
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Joined: Aug 28, 2017
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Location: Near Harlow, England

PostPosted: Wed Oct 11, 2017 1:42 pm    Post subject: Reply with quote

Thanks for the offer, much appreciated. Adrian will also come over and take a look, he's as keen as me to get this sorted.

Yes, hard to know whats going on. I have just been looking at it again and I can see the brass washers either side of both rods. The big end of the rod can slide a few mm back and forth between the washers on the noisy side, less so on the other.

I pulled the rod over towards me and it didn't quite touch the fly wheel on that side - I could get a 10 thou feeler in. Pushing back the other way, with a bit of pressure, it did touch the wheel. So maybe not as bad as I had first thought but still doesn't seem right to me.

Good point about witness marks, I will have another look at that.

What colour/texture gunge would you expect around the place? There is grey oily, but more viscous than oil, stuff that is picked up as the fly wheels turn. Is that normal, bearing in mind its done probably done 50 miles since rebuild?

Ref photos, I took a few but its hard to see much. Probably best if I email them if you let me have an address via PM.

Thanks again for your input.

Nick

EDIT: I just had a look at the rod from the other side and yes, there is a witness mark on the back edge.



witness mark on rod sm.jpg
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witness mark on rod sm.jpg


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kbts250m
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PostPosted: Wed Oct 11, 2017 3:17 pm    Post subject: Reply with quote

Yep, that witness mark is exactly what I would expect to see if a rod was hitting the crankshaft. Sorry to say something definitely went wrong with the crank. Either bad rebuild or somehow got damaged during engine reassembly or the engine ate something and bent the rod. Any sign of piston damage?

Normally, the crankcase self-cleans while the engine is running. There should be nothing but a very light film of clean gas/oil in the crankcase. Any type of sludge is not good and gritty feeling sludge especially not good. The metal from the rubbing that caused the witness marks could be the source of sludge and/or combustion residue blowing down through those bid ring end gap.

PM sent

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Currently - 75 Suz TS250, 02 Kaw ZX-6R

Previously - 70 Suz T350, 71 Suz TS250, 72 Suz GT380, 72 Suz TS125, 72 Suz TS250, 75 Yam YZ360B, 72 Suz GT380 diy cafe racer, 80 Suz GS750, 73 Suz TS185, 82 Suz GS1100
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fodder
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PostPosted: Thu Oct 12, 2017 1:03 am    Post subject: Reply with quote

What sort of things could have gone wrong on the rebuild, to have caused that? If it was an error I really don't want it repeated next time Shocked

There is no damage to the piston, and the rod looks perfectly straight as far as I can tell with it in place.

I'm resigned to getting the engine split again (those crank cases will need cleaning out), and having the crank guy look at the crank.
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dorT500
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PostPosted: Thu Oct 12, 2017 12:27 pm    Post subject: Reply with quote

I'm wondering if the gook you are seeing is a mixture of two-stroke oil, fuel and grease the crank builder may have put on the center seals.

I tried to find the crank dimensions on that engine but did not find yet. I'm going to post these as long as I have them handy. Might help someone else in the future.

Page 7 and 8

http://www.ozebook.com/compendium/techbuls/SerBulletin%20Specifications%206-9.pdf

Stand by, I'm looking for some big end tolerances.

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dorT500
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PostPosted: Thu Oct 12, 2017 1:27 pm    Post subject: Reply with quote

hhmmmm....Do you have a Suzuki factory service manual for your bike? Here are some T500 crank tolerances for what they are worth.....






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Last edited by dorT500 on Thu Oct 12, 2017 3:49 pm; edited 1 time in total
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fodder
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PostPosted: Thu Oct 12, 2017 1:52 pm    Post subject: Reply with quote

Thanks, thats helpful again.

Just 3mm movement would be very nice! Even without a dial gauge its very obvious that there is more movement than that on mine.

You're right, I'm sure, the gunge probably is a mixture of stuff. The texture is between oil and grease. The colour is odd, though - I've seen plenty of nice clean oil, 2-stroke red, or golden 4 stroke or transmission. And I've seen plenty of black dirty oil. But not this curious grey colour.

Anyway, engine will come out at the weekend, crank cases will be separated and the crank brought out into the open to reveal its nasty little secrets!
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dorT500
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PostPosted: Thu Oct 12, 2017 3:52 pm    Post subject: Reply with quote

fodder wrote:
.......... But not this curious grey colour.
Like powdered aluminum?.... Sad Just a rhetorical question. Here's hoping you have it all sorted out soon. Thumbsup
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dorT500
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PostPosted: Thu Oct 12, 2017 4:31 pm    Post subject: Reply with quote

I know you and Adrian will figure out the problem when you get it apart......

this is just an observation on my part of the T500 crank pages I posted above. It seems to me that the big end is suppose to be shoved tight to one side of the crank wheel and the big end held firmly in place (does not specifically mention doing this as in some other manuals) while you rock the small end back and fourth. This is so small end rod shake (or part of it) won't be mistaken for normal(within limits)big end side to side play ...........like I said, just an observation of the T500 manual pages and not in any way am I suggesting your measuring technique is flawed...........it's obvious the crank needs to be pulled and checked out anyway. Good Luck

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fodder
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PostPosted: Sat Oct 14, 2017 8:45 am    Post subject: Reply with quote

Thanks for the thoughts. Feel free to question my measuring techniques, its over thirty years since I've been inside a 2-stroke engine and I was a novice then too!

I think if I was getting the same results both sides I would question whether I was measuring correctly and be more inclined to think the play was normal. The one side feels fine, the other doesn't, though, and there was definitely metal hitting on metal which can't be normal.

I have taken the engine out and split the cases this morning. I can’t see anything wrong internally. Everything was located as it should be, the pegs were in their holes in the bearings, the flywheels seem well located, all was moving freely, no tell-tale signs of spinning bearing outers….

I measured the side to side movement at the small end of the con rods, with a steel rule – I don’t have a dial gauge. The RHS was about 2.5mm, the LHS was double that at about 6mm, double the limit according to your post with the tech info.

I will contact the crank builder, get his input and hopefully get him to check his work and correct as necesssary, if it was a build error/component failure

Incidentally, I'm jealous of your T500 without even seeing it. When I sort this T20 out a T500 would make a great next project Very Happy
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dorT500
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PostPosted: Sun Oct 15, 2017 11:38 am    Post subject: Reply with quote

fodder wrote:
............if it was a build error/component failure .........
Is this company anywhere near you? Might let them look at it.

http://www.themotorcycleworks.co.uk/index.php/servicing-and-repairs/

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fodder
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PostPosted: Mon Oct 16, 2017 1:54 pm    Post subject: Reply with quote

Thanks for the thought. Its about 75 miles which for you guys is nothing but for us is about two hours of traffic! I had a quick look at the site and they mention doing modern machinery rather than classics.

I spoke to the crank guy today and he is happy to take a re-look at it, so its going back tomorrow. If it comes back OK then I will have another go at the rebuild, with decent rings.
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dorT500
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PostPosted: Mon Oct 16, 2017 2:29 pm    Post subject: Reply with quote

fodder wrote:
Thanks for the thought. Its about 75 miles which for you guys is nothing but for us is about two hours of traffic! I had a quick look at the site and they mention doing modern machinery rather than classics.
I was thinking about how far it would be to ship it. BTW....that's Pete O'dells new website I gave you.....he goes waaaayyy back as far as working on these old machines' guts. Wink Good that your crank re-builder is working with you. Good Luck
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kbts250m
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PostPosted: Tue Oct 17, 2017 10:58 am    Post subject: Reply with quote

I checked out your pics and the measurement data. I suspect the greyish color of the gunk is due to some extra fine metal particles in the mix. You could see if it sticks to a magnet.

I've been trying to find the recommended side play for your bike and have not found it anywhere so far. Back in my shop day I rebuilt lots of cranks (mostly MX bikes but some twins and triples too) and I would measure the distance across the flywheels before disassembly, and re-assemble to the same dimension. That doesn't help you though.

I recall there was always some side play but it was minimal and definitely not anywhere close to enough that the rod could touch a flywheel on either side. 6mm is almost 1/4" and I guarantee you that's waaaay too much. Frankly, I don't even remember them being as much as 2.5mm, and additionally I remember using a feeler gage to be sure I didn't press them together too far. How thick a feeler? Sorry, I just don't remember.

Maybe you could try contacting these guys...
http://www.kenoconnorracing.com/Crankshaft%20Rebuilds.html
...and asking them if they have done them in the past and/or if they have specs.

I wish I could be more helpful.

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Currently - 75 Suz TS250, 02 Kaw ZX-6R

Previously - 70 Suz T350, 71 Suz TS250, 72 Suz GT380, 72 Suz TS125, 72 Suz TS250, 75 Yam YZ360B, 72 Suz GT380 diy cafe racer, 80 Suz GS750, 73 Suz TS185, 82 Suz GS1100
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fodder
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PostPosted: Wed Oct 18, 2017 4:04 am    Post subject: Reply with quote

You have been very helpful, and its much appreciated!

The crank was picked up yesterday and is on its way back to the crank builder. I suspect that the new big ends have failed or were not up to spec. but have to wait now to see what he says.
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kbts250m
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PostPosted: Wed Oct 18, 2017 5:43 am    Post subject: Reply with quote

Such huge side clearance is really weird. If it was just a matter of not pressing the flywheels close enough together then whole crank would be too long, bearings offset in relation to the crankcases, etc. I'm not even sure a crank like that would fit into the crankcase. That makes me suspect you have some incorrect parts. When the crank was rebuilt, did they replace the rods?

Note - pressed together ball and roller bearing cranks like yours (and most 2-stroke engines in general) cannot be re-machined and fitted with oversize bearings like with car engines. There is no re-machining option for the rods either. Rebuilding = replacing parts. I would expect a rebuilt crank to come back with EVERYTHING new except the flywheels (and spacers and oil slinger plates if applicable).

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Currently - 75 Suz TS250, 02 Kaw ZX-6R

Previously - 70 Suz T350, 71 Suz TS250, 72 Suz GT380, 72 Suz TS125, 72 Suz TS250, 75 Yam YZ360B, 72 Suz GT380 diy cafe racer, 80 Suz GS750, 73 Suz TS185, 82 Suz GS1100
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