Topic: CR750 resurrection

[davomoto]

Thanks PeWe!
I found a similar thickness base gasket in the box of gaskets that came with it. Is your cylinder modified to accept the o ring?

[MRieck]

You don't need the oring...use some 3 Bond etc around the base gasket. There is no space for an oring

[davomoto]

You don't need the oring...use some 3 Bond etc around the base gasket. There is no space for an orange.

Thanks!

[PeWe]

The grey sealer I used was 3 bond plus a number (1184). Look, smells and acts like Hondabond.(Not the RTV version)

[davomoto]

Thanks. I have plenty of Hondabond from doing 305 engine cases.

[davomoto]

Looks like Venolia is the piston manufacturer

[davomoto]

Pics of top and bottom

[davomoto]

I removed all 4 pistons for cleaning. They are numbered 1-4 so easy enough to keep track of. Going to reinstall them I can't determine which way is forward. Valve pockets are the same size, they are offset. Anyone have knowledge of proper orientation, or can they go either way?

[carnivorous chicken]

Very cool project, awesome go fast stuff, but just wanna say -- I am groovin' on that paint job as well.

[PeWe]

Sure the valve reliefs have same size?
If one is a little wider, it is for the IN valve.
Can be a good idea to orient them as they sat.
They have been used and married to the bores with scuff marks in one way.
They look like they are not much used.

Piston look like grinded a little.
This to balance the weight.

Have you neasured the cam lift?
Nir exact, but close.
Total lobe measurent - base circle
If closer to 0.400" lift or more
Ex can have a little lower lift

[davomoto]

Sure the valve reliefs have same size?
If one is a little wider, it is for the IN valve.
Can be a good idea to orient them as they sat.
They have been used and married to the bores with scuff marks in one way.
They look like they are not much used.

Piston look like grinded a little.
This to balance the weight.

Have you neasured the cam lift?

Have not measured cam lift but one pocket is ineed 1mm deeper and a few mm longer, towars the center of the pison, same width.
Nir exact, but close.
Total lobe measurent - base circle
If closer to 0.400" lift or more
Ex can have a little lower lift

[davomoto]

Very cool project, awesome go fast stuff, but just wanna say -- I am groovin' on that paint job as well.

Thanks CC. I'm digging the paint scheme as well!!!

[davomoto]

One pocket is 1mm deeper and 3mm longer, towardrs center of piston so pretty sure that's the intake side. I have not measured the lobes.

[PeWe]

Pistons were correctly oriented, right?

The cam stamp 25X1 is a short mark for 125-X12 ?   (Megacycle)

[davomoto]

Pistons were correctly oriented, right?

The cam stamp 25X1 is a short mark for 125-X12 ?   (Megacycle)

Yes correctly oriented! Mega cycle is 10 minutes from our shop and my partner goes way back with him. We have a box of camshafts we plan to drop with him and have him ID and note lift and duration for each.

[MRieck]

One pocket is 1mm deeper and 3mm longer, towardrs center of piston so pretty sure that's the intake side. I have not measured the lobes.

The intake relief is the larger one 99% of the time in an ICE. The Yamaha 5 valve engines were an exception and there are some others. That cam is pretty stout with a lot of lift and duration.....especially lift. I don't know how friendly that would be on the street and it will definitely need compression to work.

[davomoto]

One pocket is 1mm deeper and 3mm longer, towardrs center of piston so pretty sure that's the intake side. I have not measured the lobes.

The intake relief is the larger one 99% of the time in an ICE. The Yamaha 5 valve engines were an exception and there are some others. That cam is pretty stout with a lot of lift and duration.....especially lift. I don't know how friendly that would be on the street and it will definitely need compression to work.

I know it was a running and ridden engine build with more than a few miles on it. I believe it was removed because of bad oil leakage. I think he was planning to install the JMR billet block that I found with the other parts that measures 70mm with Wiseco 12:5 to 1 piston kits.
That most likely will be used on a different engine build as I want to build a more upright riding position version that I can ride for more than a half hour. We do a ride every year in Nor Cal called the Moto Melee, 850-900 miles over three days with lots of twisty roads, some dirt roads and some fast stuff.  Over 100 riders, pre 1971 bikes, quite a fun event!! I'm thinking dependable but definitely more power and a lot less wight than stock. Probably 836cc but I have a lot to learn about these engines. I really appreciate all of the knowledge that has been shared so far!!!!

[MRieck]

One pocket is 1mm deeper and 3mm longer, towardrs center of piston so pretty sure that's the intake side. I have not measured the lobes.

The intake relief is the larger one 99% of the time in an ICE. The Yamaha 5 valve engines were an exception and there are some others. That cam is pretty stout with a lot of lift and duration.....especially lift. I don't know how friendly that would be on the street and it will definitely need compression to work.

I know it was a running and ridden engine build with more than a few miles on it. I believe it was removed because of bad oil leakage. I think he was planning to install the JMR billet block that I found with the other parts that measures 70mm with Wiseco 12:5 to 1 piston kits.
That most likely will be used on a different engine build as I want to build a more upright riding position version that I can ride for more than a half hour. We do a ride every year in Nor Cal called the Moto Melee, 850-900 miles over three days with lots of twisty roads, some dirt roads and some fast stuff.  Over 100 riders, pre 1971 bikes, quite a fun event!! I'm thinking dependable but definitely more power and a lot less wight than stock. Probably 836cc but I have a lot to learn about these engines. I really appreciate all of the knowledge that has been shared so far!!!!

Judging by the wear pattern on the valve tips it had very little run time.

[newday777]

One pocket is 1mm deeper and 3mm longer, towardrs center of piston so pretty sure that's the intake side. I have not measured the lobes.

The intake relief is the larger one 99% of the time in an ICE. The Yamaha 5 valve engines were an exception and there are some others. That cam is pretty stout with a lot of lift and duration.....especially lift. I don't know how friendly that would be on the street and it will definitely need compression to work.

I know it was a running and ridden engine build with more than a few miles on it. I believe it was removed because of bad oil leakage. I think he was planning to install the JMR billet block that I found with the other parts that measures 70mm with Wiseco 12:5 to 1 piston kits.
That most likely will be used on a different engine build as I want to build a more upright riding position version that I can ride for more than a half hour. We do a ride every year in Nor Cal called the Moto Melee, 850-900 miles over three days with lots of twisty roads, some dirt roads and some fast stuff.  Over 100 riders, pre 1971 bikes, quite a fun event!! I'm thinking dependable but definitely more power and a lot less wight than stock. Probably 836cc but I have a lot to learn about these engines. I really appreciate all of the knowledge that has been shared so far!!!!

Very cool that you got the billet block. That is from MRieck/JMR.

[PeWe]

Mike's Billet block gives a special look
With almost stock look or 4-2-1.
Below spring pictures, best part of the year.

[davomoto]

  Yes it does!!! Beautiful bike, what a sleeper, love it!!

[davomoto]

Back on the CB750 after healing from a broken rib riding my dirt bike!! Degreeing in the cam. Got the cam card from Megacycle, it states opening at 29 degrees BTDC at 0 valve lash .040. The sprocket that was on it has 3 different bolt positions with marks 8A and 5A. As I now have it, it opens .040 at 33 degrees BTDC. First time degreeing in a cam so wondering is this acceptable, do I need a slotted sprocket? I did find true TDC with a piston stop. When I do lobe center it's also off 4 degrees so pretty sure I'm doing everything properly.

 Thanks in advance!!!!

[davomoto]

Pics

[newday777]

Back on the CB750 after healing from a broken rib riding my dirt bike!! Degreeing in the cam. Got the cam card from Megacycle, it states opening at 29 degrees BTDC at 0 valve lash .040. The sprocket that was on it has 3 different bolt positions with marks 8A and 5A. As I now have it, it opens .040 at 33 degrees BTDC. First time degreeing in a cam so wondering is this acceptable, do I need a slotted sprocket? I did find true TDC with a piston stop. When I do lobe center it's also off 4 degrees so pretty sure I'm doing everything properly.

 Thanks in advance!!!!

Your cam sprocket is likely from R.C. Engineering. There was a discussion on them (by donr maybe?) A week or 2 ago.
A day or 2 after I was reading the discussion, I had a visit from Mike R delivering my new Billet Block 1026 and while here Mike says I have something for you. It was one of these cam gears which had come off or RC's triple motor.

[davomoto]

Makes sense Stu as it has other RC internal engine parts.