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Hello.Are you getting bored looking at engine parts? Hope not ... because that's what we do. Last week's activities: Rul...
05/30/2026

Hello.

Are you getting bored looking at engine parts?
Hope not ... because that's what we do.

Last week's activities:
Rule of thumb ..... always have several jobs in the works when waiting on parts.

So,
Here is another lower end for a AHRMA formula 750 road racer going together.

1st two photos: (engine case procedures)
Disassemble an engine.
Clean for visual inspection.
Kwik measurement check of main bearing areas.
Remove cylinder studs.
Chase all 6 and 8mm threaded holes.
Heli-coils or welding if needed.
Install sandblasting covers and blast. Covers are to keep sandblast media out of the inside to cause problems.
Perform breather modifications. 7 different areas.
Line lap engine cases for perfect straightness and roundness.
Measure and fit coated crankshaft main bearings to .0015 to .002.
Install finished crankshaft to check endplay and smooth rotation.

3rd and 4th photos.

3rd photo:
Here is another lightened crankshaft given to us to use in the engine. Not that great.
Note:
Notice the "blind hole" ball bearings in the crankshaft ... the bearings are to block off the oil hole that was drilled to join the main journal to the rod journal.
The lightened crankshaft still has the bearings in them and were hit with the cutter when lightening crankshaft.
Plenty of circumstances have happened when the compromised bearings have fell out ...... loss of oil pressure of course.
4th photo:
Here is an example of the crud building up in the "blind hole" area and waiting to block-off the connecting rod oiling hole.
We have seen videos where people simply recommend spraying brake cleaner through the oiling holes without removing the ball bearings and saying your good. Nope!

5th photo:
When properly removing the valve guides for new guides ...... the valve hole should look like this ...... perfect.

New product for the Honda cb750 sohc racing world.5mm redesigned valve guides.Highest-level cast-iron material. This is ...
05/24/2026

New product for the Honda cb750 sohc racing world.

5mm redesigned valve guides.
Highest-level cast-iron material. This is the same cast iron material we have been using for years for street and racing.
Longer on the topside for more support but still retains plenty of room for large camshafts.
Slightly changed taper in the port side.
All products made by Kibblewhite for us.

Some 5mm valve history.
5mm valve kits have been around and raced for over a decade with great success in the TQ mini sprint car world (Honda engine powered)
TQ mini sprint car racing is most demanding a Honda cb750 engine has ever seen.
We purchased the remaining inventory of valve kits from Kibblewhite and decided upgrade the valves guides.

5mm weight savings:
34mm intake valve with a stock 6.5 stem is 48 grams.
34mm intake valve with a 5mm stem is only 38 grams.
28mm exhaust valve with a stock 6.5 stem is 43.5 grams.
28mm exhaust valve with 5mm stem valve is 30 grams.
Less weight.
Less spring pressures.
Less port obstruction.
Less rocker and camshaft wear.

New guides to be completed in 6 to 8 weeks.

Speaking of engine component weights.
The 2nd photo shows a 21.30 stock weight crankshaft and a 17.20 crankshaft.
The 17.20 crankshaft was tried many years ago on our race bike.
We eventually settled on crankshafts in the 20 lb range.

Hello.Next years featured AHRMA Formula 750 class is gaining momentum and not that far off.Just a reminder, 4,5,6 or mor...
05/23/2026

Hello.

Next years featured AHRMA Formula 750 class is gaining momentum and not that far off.

Just a reminder,
4,5,6 or more Honda cb750 pure race bikes will compete against the top vintage race bike brands still in existence.

Not much breaking news at the present or is there?

1st photo.
The development of cylinder head with new thoughts for road racing and hot street life is coming along nicely. Details coming soon.

2nd photo.
2 more AHRMA engines in the beginning stages.

3rd photo.
Just random back shop stuff.

The AHRMA engine build continues.Always kinda fun to get "the look" correct in the first two photographs. Not the actual...
05/19/2026

The AHRMA engine build continues.

Always kinda fun to get "the look" correct in the first two photographs. Not the actual top end.
Why?
You look good ... you race good.
You race good ... you feel good.
You feel good .... it's a good thing.

The lower end is "buttoned up" and is perfect.
Notice the primary chain adjuster screw in the last photograph.

Dumb question. Are you familiar with the inside of a Honda cb750 engine from 69 thru 78?Well,Here is a full mod lower en...
05/19/2026

Dumb question.
Are you familiar with the inside of a Honda cb750 engine from 69 thru 78?
Well,
Here is a full mod lower end engine being prepared for the 2027 AHRMA formula 750 class. (You should go to next year's races)
The difference in lower ends from a stock engine build and full race engine are similar .... But we are refining the procedures, products and permitters Honda has given us.
On the other hand,
There are many, many changes to this lower end for high horsepower and racing demands.
Feel free to ask specific questions.

Hello.The "full mod" formula 750 lower end will be going together shortly.But first .... a quick "mockup" for the owner...
05/16/2026

Hello.

The "full mod" formula 750 lower end will be going together shortly.
But first .... a quick "mockup" for the owner to see his color scheme vision.

Primary chain tensioner revisited, continued and perfected.Done!With AHRMA (American historic racing motorcycle associat...
05/16/2026

Primary chain tensioner revisited, continued and perfected.
Done!

With AHRMA (American historic racing motorcycle association) featuring the formula 750 class in 2027 ..... it seemed like the perfect time to refine the primary chain tensioner system.

Road racing takes aggressive riding, and parts reliability demands to the "highest level".

To control the primary chains from dealing with abrupt acceleration and deceleration .... here are a few features of the system.

The chains are allowed to free flow to a certain extent (1/4 to 3/8 of an inch) with mild spring pressure before the rubber "bump stop" comes into play.
Adjustments are made by removing the oil pan, turning a screw until the adjuster removes any slack and lock it down.
Simple instructions will be included.

Features:
Completely USA made.
Stainless steel adjustment bar.
PA-46 rubbing block.
Quieter throughout the RPM range.
Smoother shifting has been noticed.
Longer sprocket life on crankshafts and chain wheels.
Longer chain life.

Note:
The last photograph shows an upper slider being perfected for ultimate chain control.

4/26/2026The Honda cb750 primary drive system revisited. With the 2027 featured AHRMA F750 road racing class gaining int...
04/26/2026

4/26/2026
The Honda cb750 primary drive system revisited.
With the 2027 featured AHRMA F750 road racing class gaining interest and momentum ... we are focusing on some old thoughts and early progress with the primary drive system.

Chains:
The #1 chain manufacture in the world with the cryogenically process applied makes them the best choice for street and racing ... proven performance.

Chain wheel:
The 12 Honda rubbers in the original chain wheel to cushion shock loads worked pretty well in stock machines for 50 plus years. (unavailable from Honda)
The problem is the chain wheel sprockets are allowed to much movement and can shear the rubbers in half during abuse.
We have installed an internal travel limiting system to avoid shearing.
Also,
We have switched our cush drive rubber selection to a HMBR commercial grade composition ...... the best available.

The tensioner:
As a reminder ... we have pulled out a tub of previous parts, notes and drawings from years ago. (last photograph)
Rather than trying to reinvent the complete system .... we have incorporated rubbing blocks and partial design from the Harley world.
The Harley system has a 40 plus year success with a near perfect record.
Although, we felt a design up-grade was needed.

Here are some features:
Manually adjusted from under the oil sump pan.
Spring loaded to let the chain "do its thing" and free flow.
We have limited the chain deflection to 3/8 of an inch before the "bump stop" comes into play.
The bump stop has a HMBR rubber installed to cushion the blow during severe abuse.

Adjusting:
Simply remove the oil pan and turn the adjuster until the spring just touches and lock it down ...... you now have the perfect adjustment.
No measuring.
Follow the same procedure until the chain "settles in" or needs further attention.

Note:
The photos of the tensioner are a prototype ..... the actual tensioners are in full production.

Properties of HNBR
HNBR combines elasticity with high tensile strength, abrasion resistance, low compression set, and excellent resistance to oils, fuels, ozone, and many chemicals.

Cryogenic metal treatment is a process that exposes metals to ultra-low temperatures to improve durability, wear resistance, and structural stability.
What is Cryogenic Metal Treatment?
Cryogenic metal treatment, also known as cryogenic processing, involves cooling metal components to extremely low temperatures, typically around -300 °F (-184 °C), to modify their microstructure and relieve residual stresses. Unlike traditional heat treatment, which uses high temperatures to alter metal properties, cryogenic treatment enhances the internal crystalline structure without adding heat.

4/24/2025Another week in the books.Here is my favorite area of the shop with more engine cut-a-ways to develop Honda cb7...
04/24/2026

4/24/2025
Another week in the books.
Here is my favorite area of the shop with more engine cut-a-ways to develop Honda cb750 products.
We need to thank all of the Honda cb750 racers for solid input on potential weaknesses with the growing power of the Honda cb750 engines.
Speaking of developing products .... with the 2027 AHRMA featured formula 750 class coming soon the road racing Honda world has exposed a potential weakness.
With extreme deceleration or engine breaking we developed a primary chain tensioner for race/stock bikes to control the chains.
Very nice.
We will post some details in a day or two.

4/18/2026 Quest to build a perfect Honda cb750 continues.Re-visiting, re-thinking and re-introducing the Honda cb750 "D ...
04/19/2026

4/18/2026
Quest to build a perfect Honda cb750 continues.

Re-visiting, re-thinking and re-introducing the Honda cb750 "D shaped" exhaust port area.

The CycleX Honda vintage heavy weight superbike AHRMA road racer featured a version of a D shaped exhaust port and worked very well (2013)

Velocity increases and a reversionary exhaust flow prevention.

Reversionary meaning:
The backward flow of the exhaust gases into the intake system contaminating the fresh air/fuel mixture ..... generally, with large camshaft overlap.

Note:
Photos are in the beginning stages of the re-visit ..... be nice!

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More meaning:
Meaning of Reversionary Exhaust with Big Overlap Camshafts
Reversionary exhaust refers to the phenomenon where exhaust gases flow backward into the intake system, contaminating the fresh air–fuel mixture. This happens when there’s a pressure difference — usually low intake manifold pressure (vacuum) and high exhaust system pressure (backpressure) — during valve overlap Summit Racing.

How it works with big overlap cams
On performance camshafts with long intake and exhaust valve overlap, the exhaust valve stays open longer than it should. At low to mid RPM, the piston’s upward motion and intake valve opening can create a low-pressure zone in the intake, while the exhaust system still has high pressure. This pressure difference pushes exhaust gases back into the intake, reducing the amount of fresh charge available for combustion Summit Racing+1.

Key factors that worsen reversion with big overlap cams:

Excessive valve overlap — more time for exhaust gases to travel back into the intake harleytechtalk.com.

High backpressure in the exhaust system — stock or restrictive headers can amplify the effect Summit Racing.

Low RPM operation — where vacuum is highest and scavenging is less effective Summit Racing.

Effects on performance
Reduced power at idle and low RPM due to diluted intake charge Summit Racing.

Lower intake vacuum and poorer idle quality Summit Racing+1.

In severe cases, fuel can “stand” in the carburetor or be pushed into the air cleaner, and exhaust soot can appear in intake runners Summit Racing.

Why big overlap cams are more prone
Long overlap cams are designed to maximize scavenging at high RPM, but at low RPM the reverse flow becomes more significant. The exhaust valve’s prolonged stay open allows spent gases to travel back into the intake, especially if the exhaust system isn’t designed to handle it harleytechtalk.com.

Mitigation strategies
Upgrade exhaust flow — headers and free-flowing exhaust reduce backpressure Summit Racing.

Match components — ensure intake, heads, and exhaust are sized for the cam’s overlap to avoid mismatched airflow Summit Racing.

Adjust valve timing — slightly advancing the cam can close the exhaust valve earlier, reducing the time for reversion Speed-Talk.com.

Design exhaust system — larger ports, proper header design, and avoiding restrictive manifolds help resist reverse flow Summit Racing.

In short: With big overlap cams, reversionary exhaust is a trade-off — the cam gains high-RPM power but can lose low-RPM efficiency if the exhaust system isn’t optimized. Proper airflow management and component matching are key to minimizing its impact

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