Con rod meets cylinder - advice needed

[Paulrs]

Hi all, having a small problem with my engine rebuild. The engine has been stripped down for the case to be painted, shinny bits replated and worn bits replaced. The cranks were rebuilt with new rods a couple of new webs (rust damage more than wear) and new mains. This was done by PJME and they look good and are very well aligned. The bores are standard with new pistons and rings.

The crank cases went together well, however when I tighten the nuts holding down the rear left cylinder you can no longer turn the engine a full rotation. From further investigation it looks like the con rod is just contacting the very bottom of the cylinder barrel. If you loosen the nuts on the barrel a turn the engine will turn over fully, but you can see the back of the barrel lift a fraction of an mm at the point where it had jammed.

Anybody else had this problem? Any suggestions?

Thanks
Paul

[Rick Lance]

If the rods aren't factory 47X rods, I would suspect that the aftermarket rod has a larger big end support area and is the root of your problem.

[BRIAN TURFREY]

Yes, Mr Rick Lance is very correct.

After i put a set of aftermarket ( brand new Gus crank's ) in a motor, had the same kinda problem? When you hand turn the motor over, you can feel something hit? After measuring a set of stock Yamaha RZ500 cranks and Gus's crank's, the rods on Gus's cranks ( which do have a 47X on them ) are clearly much bigger at the bottom of the rod beam and will tip the case. Seem's like nobody else that builds these motors ( expect Mr Rick Lance ) has had this problem, but seems like they never checked? until now i bet

[Paulrs]

Thanks for the replies.

It is difficult to measure with an assembled bottom end, so I made a cardboard template to compare the con rod shape with an old crank (as it came from Yamaha apart from the wear!). The bottom of the rod where it transitions from the machined part around the big end to the forged section extends a little further up the rod on the new one. Obviously just enough to clip the bottom of one, not all, of the cylinder barrels.

Since posting, I have heard from another owner who had the same issue as Brian and I, so the problem does not seem unique.

The solution appears to be grinding the very bottom corner of the barrel away until it clears. I would do this with the gasket removed, so once fitted I would be sure of a safe clearance.

Can anybody see an issue with this approach?

For info, both the old and new con rods are marked 47X and look identical to the human eye.

Thanks
Paul

[podman]

Couls you also ask PJME their thoughts if they built the cranks Paul?

[silverstrom]

Who was the original supplier of the rods?

Not that this is necessarily your issue, but many offshore supplied parts look identical to stock, including stamps and embossing, and are difficult to discern from high quality dimensionally correct parts. Offshore suppliers are very good at producing reproduction parts that exactly replicate OEM in every way except quality and exacting dimensions.

[BRIAN TURFREY]

You may want to check..... very closely where it is hitting, the one i had was hitting the inside of the cases... at the top edge ( as the rod would start/finish the swing through the cases not the base of the cylinder? So motor came completely apart and you could clearly see the mark on the rod/case where it hit. If you send me a e-mail i will forward you pictures so you can see. People said i was using "offset" pistons, which would make things worse, but ha... using pistons with no offset pin
The fact is, while Gus's cranks are nice.... the rods are "NOT" the same spec as stock RZ500 at the big end... and Mr Rick Lance called it right in my book

Good luck, hope this helped you

Brian

[Paulrs]

Yep, will be giving PJME a call in the morning. They have been shut since discovery of the problem on Saturday night.

Rod is definitely touching the base of the barrel as everything is fine until the rear left one goes on.

I have read some comments about offset pistons and not really got a full understanding of that subject. But I was going to see how it assembled with the old Pistons before I go too far, just in case there is a difference.

Thanks for all the advice.

Paul

[podman]

Yep, will be giving PJME a call in the morning. They have been shut since discovery of the problem on Saturday night.

Rod is definitely touching the base of the barrel as everything is fine until the rear left one goes on.

I have read some comments about offset pistons and not really got a full understanding of that subject. But I was going to see how it assembled with the old Pistons before I go too far, just in case there is a difference.

Thanks for all the advice.

Paul

What did they say then Paul?

[silverstrom]

http://www.rzrd500.com/500phpBB3/viewto ... =3&t=13905" onclick="window.open(this.href);return false;

Just so the topics cross reference both ways.

Looks like PJME has some explaining to do.

[WVWRZ500N]

Ever since OEM rods went NLA I've been using the Yambit's rods. True they are not the 'same' as OEM being larger on the big end also. However, having built several with these I've yet to have one hit anywhere during rotation.

Regards,
Bill Wilson
Wilson Performance
Lee's Summit, MO
http://www.wilsonperformance.net" onclick="window.open(this.href);return false;
Member RZ500 Owners Group #573
816-377-3185
WVWRZ500N@aol.com

[MK]

I've had a set of rear RD500 cylinders bored with 0.5 mm DT125 Prox pistons.
They showed similar issues (I.e. did interfere with either the rod or crank webs).
The owner checked against the stock piston and found a longer piston skirt (just 1 mm). The solution was to grind it down to stock dimension.

I've used that exact setup in 1996 on my own without any issues.

[nzminis]

I have a yambits rod and some genuine ones
after i finish riding today i will take some snaps side by side

[Paulrs]

Hi All, sorry about the slow reply, but have been working away for a couple of weeks and only got round to checking the problem properly and contacting PJME this weekend.

So I could see exactly where bits were contacting I stuck a bit of masking tape on the con rod and some black felt pen on the barrel, then assembled and turned it over, results in photo's.

20160214_114025.jpg (49.49 KiB) Viewed 4808 times

20160214_113959.jpg (63.68 KiB) Viewed 4808 times

I sent the photo's to PJME and got reply back very quickly, apologizing and offering to collect the cranks and sort the problem. They commented as follows:

Sorry to hear you are having issues with your cranks, I know how frustrating it can be to get so far into he build to find a issue!! Having seen your photos and chatted with the supplier of the con rods, they did have a new batch last year and the supplier thinks from looking at their stock that some were machined slightly differently which is why the issues has arose.

I see there is another thread running on cranks from PJME, and it has some comments about the quality of their work. I can only speak as I find and say the alignment/quality of these cranks is spot on, the only issue being the profile of the con rod. Still debating grinding a small radius on the bottom of the barrels rather than returning them!

Paul

[Speed Freak]

Can you take a picture of the conrod without masking tape?
Looks a bit like the problem is in a region where the conrod is not machined (split line from casting/forging)

I would just grind away the material on the conrod (all bearings covered and wrapped in tape to protect them from dirt).
Such "burrs" are not necessary for stability, even better if the shape is as smooth as possible without small corners.