SOHC.co.uk Forums > CB750
Surprise 812 Yoshi Pistons - but will they work for me
Trigger:
With those numbers the engine is a CB 750F2, engine came black from the factory ;) Completely different from the CB750F1.
You seem to be hooked on these Yoshi pistons which, i guess have been over bored and 0.1000 is miles out even for yoshi pistons.
Are the liners Yoshi ?
Have the head studs been up graded to take the high compression ? Maybe this is why the head is leaking in the first instance.
Does it have Yoshi alloy con rods ?
Is the crank Yoshi and has it been Dynamic balanced ?
If all these answers are NO then, someone has been playing at being a engineer ;)
rem1859:
So, it seems the advice I am being given is :- Give Up! Throw the pistons away! This is different to my experience on similar forums in the past, where people made suggestions about how to make things work.
I am still no further on with the original questions.
What rings should I buy?
If I was to buy another barrel or sleeves, what would be the recommended fitment by Yoshimura?
Maybe nobody on the forum has any real experience of fitting secondhand Yoshi pistons so can't help. I am feeling a little discouraged at the moment.
Oddjob:
I can understand you thinking that. However experience on this site says that a lot of engineers get the clearance size wrong for Hondas, they either refuse to accept the right clearance and insist it will seize or just plain ignore you and bore to what they think is acceptable.
I suspect you have fallen into this category, the PO has gotten it wrong by the look of it.
Experience also shows that the Yoshi 812 kit wasn't the best idea in the world anyway, it sounded good in practice but didn't really warrant the cost involved or the problems they could create.
Best bet, buy a set of decent second hand barrels and go back to standard, it doesn't sound as cool standing by the bike telling people it's got Yoshi pistons etc but the reliability of the OE system far outweighs any cool factor IMO.
Bryanj:
Yoshi were designed as race kit with a limited life and i for one would never use second hand race parts.
From memory, and yes i built a Yoshi 500 many years ago, the life of their big kits when used on road was not high
Trigger:
--- Quote from: rem1859 on August 02, 2022, 01:59:55 PM ---So, it seems the advice I am being given is :- Give Up! Throw the pistons away! This is different to my experience on similar forums in the past, where people made suggestions about how to make things work.
I am still no further on with the original questions.
What rings should I buy?
If I was to buy another barrel or sleeves, what would be the recommended fitment by Yoshimura?
Maybe nobody on the forum has any real experience of fitting secondhand Yoshi pistons so can't help. I am feeling a little discouraged at the moment.
--- End quote ---
I have 28 years experience with Honda SOHC engines :o
The 812 pistons or rings have not been available for years. I had a Henry Abe big bore engine in for a rebuild once and that was the same, rings not available. This is a problem with any big bore kits, they do not hold stock once they have changed to another kit or the business has closed down.
Wiseco 65mm 836cc big bore kit is a option but, at about £700 + P&P +import tax + the machine work needed. And you will need a set of APE upgraded head studs. That is a very expensive option.
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